Clinical Oral Anatomy A Comprehensive Review For Dental Practitioners and Researchers
Clinical Oral Anatomy A Comprehensive Review For Dental Practitioners and Researchers
Clinical Oral Anatomy A Comprehensive Review For Dental Practitioners and Researchers
Scott Lozanoff
A Comprehensive Review
for Dental Practitioners and
Researchers
123
Clinical Oral Anatomy
Thomas von Arx • Scott Lozanoff
I want to dedicate this book to my parents, Paul and Peggy, for instilling
within me a passion for knowledge through scientific pursuit.
Scott Lozanoff
Foreword
The authors – Thomas von Arx and Scott Lozanoff – have in their introduction presented a
citation that clearly points to the importance of present-day anatomy: namely, its clinical rel-
evance. For oral- and maxillofacial surgeons, dentists, and ENT and plastic surgeons, the clini-
cal and functional anatomy of the head (and neck) is of prime significance and importance for
successful and acceptable outcomes of their surgical procedures. Detailed and firm knowledge
of orofacial anatomical structures therefore is absolutely mandatory for all those dental and
medical specialists who are “active” in the oral cavity and face.
The productive academic partnership of Thomas von Arx, an experienced oral surgeon, and
Scott Lozanoff, an authority in orofacial anatomy, is ideal in combining their knowledge and
expertise in the field of clinical anatomy.
In 26 chapters, the authors have written down and illustrated clinical anatomical features of
musculature, orofacial nerves, facial bones, and other important anatomical structures in an
extremely clear and didactic way. The text is precise and to the point. The illustrations includ-
ing schematic drawings and photographs of anatomical specimens are easy to understand,
informative, and of excellent quality.
The present book is an update of oral anatomy not only for those who have been in their
dental and medical profession for a long time but also for medical and dental students.
This book on clinical oral anatomy is a marvel and has great promise!
vii
Preface
Oral anatomy provides the basis for oral diagnosis, treatment, and care. A firm understanding
of anatomical structures and their spatial relationships is critical for all dental specialists to
remedy patient maladies and ensure holistic health. Recent innovations in dental research have
provided far greater anatomical resolution and information than was previously available. The
dental sciences have witnessed an explosion of scientific investigation over the recent years
with a dizzying array of new data to improve all aspects of clinical dentistry. With such a dra-
matic increase in information, reduction in curricular time for craniofacial anatomy is inevi-
table. However, curriculum reduction belies a fundamental fact – to achieve successful
diagnosis and treatment, the practitioner must learn and understand basic oral anatomical rela-
tionships. An anatomical knowledge base must be portable and translatable in the clinic in
spite of reduced instructional time. We believe that there is a need for an oral anatomy textbook
that provides fundamental information in a descriptive fashion but also utilizes a presentation
style that enables the interested reader to effectively obtain anatomical information required to
understand clinical intervention. Thus, we have written a textbook that focuses on fundamental
anatomical relationships presented in a concise fashion so that the most relevant information
can be found rapidly and reliably. We have endeavored to address the most important anatomi-
cal information in various presentation styles, enabling the interested reader to either read
sequentially or utilize the book as a reference and identify information for a specific purpose.
Clinical Oral Anatomy: A Comprehensive Review for Dental Practitioners and Researchers
concentrates on the oral cavity and structures that are directly contiguous. Detailed descrip-
tions are provided, focusing on spatial relationships among anatomical structures that are par-
ticularly compelling for the clinician. The descriptions are written to be direct and informative,
ensuring that the reader comprehends the information as efficiently as possible.
The written descriptions of oral anatomy are accompanied by elegantly simple illustrations
that are designed to reflect critical relationships in a visual fashion that emphasizes ease of use
and understanding. The illustrations and captions have been devised in a manner that should
enable the reader to understand the corresponding anatomical relationship without necessarily
reading the full text. Additionally, detailed cadaveric dissections were undertaken to empha-
size anatomical relationships in situ. In addition to the information provided in textual form,
this book also is intended to serve as an anatomical atlas.
Knowledge of anatomical variation of the oral region is critical for understanding symp-
toms, interpreting images, planning treatment, and providing operative management. A signifi-
cant number of malpractice cases have resulted directly from a misunderstanding of anatomical
variation. Sadly, near fatal and in some cases fatal complications arise due to a lack of appre-
ciation of atypical anatomy. There are likely genetic and ethnic components to the preponder-
ance of certain variations in specific populations. We have attempted to incorporate reports of
anatomical variation patterns and occurrence with the intention of providing a reference source
for the student and practicing clinician. In addition to qualitative descriptions of reported varia-
tions, we have painstakingly delineated quantitative descriptions of variants so that the reader
has access to the most complete information regarding possible variations within their own
clinical context.
ix
x Preface
The operational field for dental clinicians is miniature in scale where the difference between
success and failure is literally measured in millimeters. Precision is imperative, and to this end,
we have meticulously reported quantitative assessments of anatomical relationships directly
from the publications in the primary literature. These values as well as their derivative citations
are summarized in tabular form. The tables provide a quick reference for the interested reader
and reflect a novel perspective of anatomical variation.
Among the numerous and varied research breakthroughs in basic and clinical dental sci-
ences in recent years, dramatic progress has occurred in dental imaging. In particular, image
procurement using cone beam computed tomography (CBCT) has become a critical tool in
various dental specialties for assessment and treatment paradigms. We have incorporated as
many of these studies as possible and assessed the usefulness of CBCT in various settings for
recognizing anatomical spatial relationships. Imaging with CBCT is compared to anatomical
resolution utilizing other visualization methods whenever possible. Several original clinical
and radiological images are included from the Department of Oral Surgery and Stomatology at
the University of Bern School of Dental Medicine.
Cadaveric dissection provides one of the most direct and dynamic approaches to test
hypotheses concerning anatomical spatial relationships. Several meticulous dissections were
undertaken and included in this book. In many cases, the photographs provide direct evidence
for oral anatomical features that are described in the text. Many of these photographs are
unique and were included because they have not been available, to our knowledge, in the litera-
ture. They provide novel perspectives of complex features and should serve to illuminate previ-
ously unappreciated anatomical arrangements.
The anatomical information presented in this text ultimately is intended to improve clinical
problem-solving skills. Thus, all chapters include a “clinical relevance” section highlighting
the importance of the anatomical topic within a clinical context. These sections largely reflect
the considerable clinical and anatomical experience of the authors and underscore the impor-
tance of a solid foundation in anatomy.
It may seem unusual to write an orofacial anatomy book without including teeth. After
significant consideration and discussion, it was decided to leave this complex and broad topic
to other textbooks. However, we frequently refer to the many aspects of tooth morphology and
their relationship to the tissue and structures described in the text.
With all of these factors in mind, we have compiled a comprehensive guide to oral anatomy
emphasizing the most recent findings regarding quantitative assessment, advanced imaging,
and anatomical variations. We have attempted to maximize new research relevancy so the lit-
erature cited covers the period from 1990 to 2015 with some earlier landmark articles cited
where appropriate. We are hopeful that this book will provide a valuable reference guide for
dental practitioners, clinical researchers, orofacial research scientists, and craniofacial anat-
omy instructors among others eventually serving to improve oral anatomical problem solving
within a clinical context.
Anatomy has played a critically important role in our 30-year experience in oral surgery
(TvA) and basic oral biology research (SL). The lack of continuing education courses focus-
ing specifically on clinical oral anatomy has triggered our interest in writing a book on oral
anatomy. Furthermore, the introduction of CBCT in dentistry has increased the need for
understanding detailed spatial relationships between anatomically relevant structures. Taken
together, complimentary interests have deepened our curiosity to learn and teach
collaboratively.
Cadaveric dissections of the orofacial region serve as possibly the most direct and dynamic
method to test hypothesis concerning anatomical spatial relationships. This philosophy pro-
vided the primary motivation to write this book. TvA undertook a sabbatical at the University
of Hawai’i School of Medicine. The main objective was to benefit from mutual and comple-
mentary academic interests as well as to undertake comprehensive orofacial cadaveric dissec-
tions in preparation for this book. Many of these dissections are included in this book. Faculty,
staff, and students of the Department of Anatomy, Biochemistry and Physiology at JABSOM
are thanked for their helpfulness and hospitality (the famous aloha spirit of Hawai’i). In par-
ticular, Steven Labrash is thanked for providing outstanding assistance as well as outstanding
anatomical specimens, Beth Lozanoff for graphical ideas, and Tricia Yamaguchi for adminis-
trative support.
From a broader perspective, several current and former faculty and students at the University
of Hawai’i School of Medicine provided intellectual input serving to expand our anatomical
knowledge base necessary for writing this book. Faculty include Dr. Chris Stickley, Dr. Kaori
Tamura, Dr. Yukiya Oba, Dr. Takashi Matsui, Dr. Vernadeth Alarcon, Dr. Cadie Buckley, Dr.
Selcuk Tunali, Dr. Julie Rosenheimer, Dr. Beth Jones, Dr. Sara Doll, Dr. Marita Nelson, and
the late Dr. Vince DeFeo, while vital medical students include Ms. Trudy Hong, Mr. Greg
Atkinson, Mr. Chih-wei Chang, and Dr. Niket Ghandi.
Back in Bern, the most important persons to get this book on track were Bernadette Rawyler
who provided all the fantastic illustrations and Ines Badertscher who provided critical assis-
tance with image preparation that is greatly appreciated. We would also like to thank TvA’s
personal assistant, Lena Dänzer, for patient management in order to obtain clinical pictures
and for assisting literature searches and obtaining selected articles. We also greatly acknowl-
edge the staff of the University of Bern Dental Radiology Section for taking and providing the
two- and three-dimensional radiographs used in this book.
Special thanks go to Prof. Dr. Daniel Buser, Chair of the Department of Oral Surgery
and Stomatology, School of Dental Medicine, University of Bern, Switzerland, for mentor-
ing the academic career of TvA and supporting TvA’s interest in orofacial anatomy; special
thanks also to Prof. Dr. Michael Bornstein, Associate Professor, Section of Radiology,
Department of Oral Surgery and Stomatology, School of Dental Medicine, University of
Bern, Switzerland, for intellectual input and collaboration in many radiographic-anatomi-
cal studies.
We thank the staff of Springer for bringing this book to life, especially Mrs. Tanja Maihöfer
and Mrs. Wilma McHugh for their assistance and patience.
xi
xii Acknowledgments
Last but not least, our thoughts are with the thousands of people who donate their bodies
annually for health education and research. Their contribution to the study of anatomy forms
the foundation of medicine and dentistry underscoring the maxim – Anatomy: The Oldest
Child of Mother Medicine (Tubbs S, Editorial, Clinical Anatomy 2014;27:805).
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Oral Fissure and Lips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Smile Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Clinical Relevance of the Oral Fissure and Lips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3 Vestibule and Cheeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Clinical Relevance of the Vestibule and Cheeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4 Parotid Glands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Facial Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Auriculotemporal Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
External Carotid Artery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Retromandibular Vein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Clinical Relevance of the Parotid Gland and the Facial Nerve . . . . . . . . . . . . . . . . . . . 43
Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5 Anterior Maxilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Clinical Relevance of the Anterior Maxilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
6 Infraorbital Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Infraorbital Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Infraorbital Foramen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Multiple Foramina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Infraorbital Nerve and Artery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Canalis Sinuosus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Anterior Superior Alveolar Nerve and Artery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Middle Superior Alveolar Nerve and Artery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Clinical Relevance of the Infraorbital Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7 Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Radiography of the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Morphology of the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Angulation of the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Width and Length of the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Distances from the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Content of the Nasopalatine Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
xiii
xiv Contents
AA Angular artery
AbN Abducens nerve
AC Alveolar crest
AD Articular disk
AE Articular eminence
AEA Anterior ethmoidal artery
AIOF Accessory infraorbital foramen
ALa Antilingula
ALN Ala of nose
AMA Accessory meningeal artery
AMC Accessory maxillary canal
AMF Accessory mental foramen
AN Anastomosis
ANe Anastomosis (extraosseous)
ANi Anastomosis (intraosseous)
ANS Anterior nasal spine
AOM Angulus oculi medialis
APA Ascending pharyngeal artery
APalA Ascending palatine artery
APC Adipocytes
APG Accessory parotid gland
ARF Anastomosis between RMV and FV
ASAA Anterior superior alveolar artery
ASAN Anterior superior alveolar nerve
AT Articular tubercle
ATN Auriculotemporal nerve
AV Angular vein
BA Buccal artery
BBP Buccal bone plate
BF Buccal frenum
BFe Bone fenestration
BFP Bichat’ fat pad
BiMC Bifid mandibular canal
BM Buccinator muscle
BMc Buccal mucosa
BMlp Buccinator muscle (lower part)
BMup Buccinator muscle (upper part)
BV Blood vessel
C Canine
CaNF Canaliculus to nasal floor (from CSin)
CBCT Cone beam computed tomography
CC Carotid canal
xix
xx Abbreviations
ZA Zygomatic arch
ZB Zygomatic bone
ZFF Zygomaticofacial foramen
ZFS Zygomaticofrontal suture
ZMA Zygomaticomaxillary arch
ZMa Zygomaticus major muscle
ZMi Zygomaticus minor muscle
ZMS Zygomaticomaxillary suture
ZN Zygomatic nerve
ZTS Zygomaticotemporal suture
Introduction
1
The introduction of clinical relevance has transformed the study larynx via the oral cavity, anesthesiology for oral intubation
of anatomy from an insufferable mandatory first-year hurdle to a
and nerve block administration, pneumology during the
meaningful experience on which to build a successful career in
the practice of dentistry. Bernard Liebgott (Professor Emeritus, examination of the trachea via the oral cavity, and gastroen-
Department of Surgery, Division of Anatomy, University of terology in the case of examination of the esophagus via the
Toronto, Canada) oral cavity. Other professionals working indirectly with the
The oral cavity is an important part of the skull with mul- oral cavity include vocal coaches, speech therapists, physio-
tiple physiologic functions such as deglutition including bit- therapists, and chiropractors.
ing and mastication, swallowing, phonation, and respiration. Since the mouth is considered a part of the face, it also
Hence, a healthy and functioning oral cavity is a prerequisite contributes to facial expression with movements of the lips
for life and well-being. Unique structures of the oral cavity and jaws and with the associated musculature. Smiling is
include the teeth, the gingiva, and the tongue that are all considered one of the principal facial expressions and highly
highly specialized tissues, in particular for eating and speak- valued for nonverbal communication. Any anatomical varia-
ing, and, as such, are not found in other parts of the body. tions resulting in a disturbance of mimics is readily visible
The oral cavity is located in the lower and anterior part of the and often has a psychological impact on the patient. As a
skull. The bones around the oral cavity (mandible, maxilla, consequence, psychiatrists and psychologists may also
palatine bones) belong to the facial skeleton, i.e., the viscero- include a patient’s facial expression when evaluating the
cranium. In contrast the upper and dorsal portion of the skull mood of a patient.
contributes to the neurocranium that contains the brain. The next 25 chapters describe in detail the clinically rel-
The main communications of the oral cavity are via the evant anatomy of the oral cavity including its immediate
oral fissure to the outside and via the isthmus faucium to the adjacent structures such as the maxillary sinus, the infratem-
oropharynx. However, also neurovascular structures and poral fossa, the temporomandibular joint, and the mastica-
bony canals connect the oral cavity to neighboring areas tory muscles. The sequence of the chapters follows a logic
including the nasal cavity with associated sinuses, the orbit, pathway from the oral fissure to the anterior maxilla, then via
the neck, and even the cranial cavity (cavernous sinus via the posterior maxilla and pterygopalatine fossa to the man-
venous anastomoses, middle meningeal artery from maxil- dible and eventually to the tongue and floor of the mouth
lary artery). Those “anatomical” communications may (Fig. 1.1). However, each chapter describing a part of the
explain untoward and distant side effects following treatment oral cavity is complete on its own; hence the clinician or
within the oral cavity. researcher seeking advice about a special anatomical struc-
The oral cavity is the territory of the dental surgeon and ture may skip to a specific chapter to obtain all the pertinent
the dental hygienist and all the subspecialties of dentistry. information.
But the oral cavity plays also an important role in many other .... that our understanding of basic anatomy is not always com-
medical specialties, such as maxillofacial surgery, the field plete, and thorough re-evaluation of what appears mundane and
intuitive can sometimes lead to new insights .... Eppley
closest related to dentistry, otorhinolaryngology requiring BL. Discussion: Cutaneous distribution of infraorbital nerve. J
the examination of the oro- and nasopharynx as well as of the Craniofac Surg 2004;15:5.
Temporo-
mandibular
Joint
Maxillary Sinus
Posterior Maxilla Anterior Maxilla
Oral Fissure
Posterior Mandible
Tongue
Floor of Mouth
Anterior
Mandible
Oral Fissure and Lips
2
The oral cavity (l, oris, mouth) forms the rostral opening of be 7 mm in infants and 9.7 mm in adults (Hennekam et al.
the digestive tract and contributes to critical functions includ- 2009). The philtrum is derived embryologically from the
ing mastication, vocalization, and respiration. It is divided labial component of the intermaxillary segment. This struc-
into a smaller external portion, the vestibule, and a larger ture marks the fusion of the maxillary prominences as they
internal component, the oral cavity proper. The vestibule grow medially and contact the medial nasal prominence.
forms as a cleft between the lips and cheeks externally and Upon fusion, both the philtrum and underlying primary pal-
the teeth internally. When the teeth are occluded, the vesti- ate form. When fusion fails, cleft lip and/or palate can result.
bule communicates with the oral cavity proper only through The lips and the perioral area play an important role for
a gap between the last molar and mandibular ramus. When attractiveness and beauty (Wollina 2013). A prominent upper
the teeth are not occluded, the vestibule communicates with lip vermilion was observed in subjects with a high smile pat-
the oral cavity proper as well as with the external environ- tern (Miron et al. 2012). The lower lip shows a regularly
ment through the oral fissure. The fissure is formed by the curved vermilion border, and its inferior limit in the central
free borders of the upper and lower lips that join each other region joins the mentolabial sulcus. The lips and the perioral
in the corners of the mouth or commissures (Fig. 2.1). facial muscles (Figs. 2.2 and 2.3) are further essential for the
The lips (labialis, superioris, and inferioris) are mobile dynamics of smiling that has been shown to be age and gen-
musculofibrous folds that meet laterally to form the cephalo- der related (Houstis and Kiliaridis 2009; Chetan et al. 2013).
metric point, cheilion (g, lips). The keratinized stratified The movement of the lips is based on a complex interaction
squamous epithelium of the external skin transitions to the of several muscles. The primary muscle of the lips is the
thin, nonkeratinized mucous membrane of the oral cavity. As orbicularis oris muscle (Fig. 2.4). It is a very strong muscle
a result, a vermilion border of the lips becomes distinguished that one can easily palpate when pursing the lips. The muscle
by the red color of the underlying blood vessels of the lamina encircles the opening of the mouth functioning as a sphincter
propria from the surrounding skin. The epithelium of the lips for the oral cavity. Initial contraction of the orbicularis oris
continues internally forming a mucous membrane that pro- closes the mouth and further contraction protrudes the lips
vides a continuous lining over all oral cavity structures (Stavness et al. 2013). It is a composite muscle formed from
except the teeth. interdigitations of the facial expression muscles inserting
External surface features of the oral fissure are complex into the lips. Usually, submuscular fat is present deep to the
and clinically important. The contour of the line formed by orbicularis oris muscle, and this fat is distinct from the more
the vermilion border of the upper lip is called “Cupid’s bow” superficial fat of the cutaneous lip (Rohrich and Pessa 2009).
(Carey et al. 2009). The upper lip is further characterized by Facial muscles originate either from bone or fascia and
an indentation of the vermilion border in its central part. insert directly into the epithelium of the face and lips. The
Below that indentation, a slight protuberance is present, muscles of the perioral region can be divided into three
while above lies a shallow groove called the philtrum (g, groups: upper, lateral, and lower. The upper group of perioral
philtron, love charm) that, along with its pillars, is consid- muscles includes the zygomaticus major, zygomaticus
ered part of the upper lip (Carey et al. 2009). The philtrum minor, levator anguli oris, the levator labii superioris, and
extends from the vermilion border superiorly to the base of levator labii superioris alaeque nasi (Figs. 2.5, 2.6, and 2.7).
the nose (subnasale). This linear interval is designated as the The zygomaticus minor (narrower in width) and zygomati-
nasolabial distance (upper lip height) with a mean value of cus major (broader in width) are located superficially below
22.5 mm in females and 24.7 mm in males (Nascimento the skin and originate from the lateral surface of the zygo-
et al. 2013). The mean width of the philtrum was reported to matic bone. They cross the midface in a medial and downward
philtral ridges
superior vermilion
upper border
lip philtrum
inferior vermilion
border
mentolabial sulcus
CSc
Pc
OOc
LLSAN NaM
LLS
ZMi LAO
OO
BM
ZMa
RiM
MO
OO
DLI
DAO
MeM
2 Oral Fissure and Lips 5
LLSAN
LLS
ZMi
ZMa OO
BM LAO
RiM MO
OO
DLI
DAO MeM
MeM
direction toward the upper lip (zygomaticus minor) and the angle of the mouth and as thus serves as the antagonist of the
angle of the mouth (zygomaticus major). This direction of depressor anguli oris. It originates from the anterior maxilla
the fibers explains the action of the muscles: upward and lat- below the infraorbital foramen and inserts laterally to the
eral movement of the upper lip and the corner of the mouth. upper lip. It contributes to the modiolus of the mouth in addi-
The levator labii superioris (LLS, also termed levator latera- tion to the other facial muscles contributing to the tendinous
lis muscle) and its medial partner the levator labii superioris chiasm lying slightly superior to the lateral commissures of
alaeque nasi (LLSAN, also termed levator medialis muscle) the oral fissure (Hur et al. 2010a, b).
are located medial to the zygomaticus minor. The LLS origi- The lower group of perioral muscles comprises the
nates below the infraorbital rim and consistently covers the depressor anguli oris, the depressor labii inferioris, and the
infraorbital foramen. The upper part of the LLS is covered mentalis muscles (Figs. 2.8 and 2.9). The depressor anguli
by the orbicularis oculi muscle (Konschake and Fritsch oris is the most superficial of these muscles. It originates
2014). The fibers insert into the skin of the upper lip lateral from the anterolateral bone surface below the premolars and
to the philtrum, sometimes reaching the labial angle. inserts in the skin near the labial commissure. It functions to
The LLSAN originates from the palpebral ligament and lower the corner of the mouth. The depressor anguli oris also
from the periosteum of the nasofrontal process of the max- contributes to the modiolus of the mouth. The depressor labii
illa. The majority of the LLSAN fibers insert into the skin of inferioris is located deep and medial to the depressor anguli
the nasolabial area and the furrow of the nasal alae. Fewer oris. The muscle originates from the mandibular cortex
fibers reach the upper lip in a medially concave arc and inter- below the canine and it fans upward and medial into the
mingle with the LLS fibers (Konschake and Fritsch 2014). lower lip.
Both LLS and LLSAN muscles function to elevate the upper This muscle both depresses the lower lip and moves it
lip (Ferreira et al. 1997). The levator anguli oris raises the laterally owing to the oblique course of its fibers. Finally, the
6 2 Oral Fissure and Lips
LLS
ZMi
OO
LAO
ZMa
MO
OO
LAO
ZMi OO
MO
OO
MO
OO
DLI
DAO MeM
MeM
OO
OO DAO
MeN DLI
MeM
MeM
10 2 Oral Fissure and Lips
OO
BM
RiM
OO
FA
2 Oral Fissure and Lips 11
SLA
FA
FA
FA ILA
LMA
MeN
FA
SCA MeA
Fig. 2.12 Latex injection and dissection of the right cadaveric oral
region demonstrating the arterial supply of the lips. FA facial artery, ILA
inferior labial artery, LMA labiomental artery, MeA mental artery, MeN
mental nerve, SCA small communicating artery between the facial
artery and mental artery, SLA superior labial artery
ILA
ILA
LMA
12 2 Oral Fissure and Lips
Fig. 2.14 Illustration of a low smile line characterized by diminished Fig. 2.15 52-year-old male with a low smile line
soft tissue visibility around the maxillary anterior teeth resulting in the
appearance of the mandibular anterior teeth
Clinical Relevance of the Oral Fissure and Lips 13
Fig. 2.16 Illustration of a medium smile line characterized by visible Fig. 2.17 27-year-old female with a medium smile line
gingival papillae of the anterior maxillary teeth and possibly the mar-
ginal gingivae of the posterior teeth
Fig. 2.18 Illustration of a high smile line characterized by an extremely Fig. 2.19 20-year-old female with a high smile line
visible facial gingiva of the anterior maxillary teeth, with some patients
occasionally showing the mucogingival line and the alveolar mucosa
located apically
The vestibule comprises the small external portion of the oral pensated by nonesthetic, extra long prosthodontic
cavity, and it forms a horseshoe-shaped space marking the reconstructions (Fig. 3.4); or vertical ridge augmentation
reflection of the mucous membrane from the lips and cheeks (Fig. 3.5) is required to reconstruct the vertical bone defi-
to the gingiva (Figs. 3.1, 3.2, and 3.3). The boundaries of the ciency (Urban et al. 2009; Cardaropoli et al. 2013; Draenert
vestibule include soft tissues of the lips anteriorly and the et al. 2014). A typical and relatively common intervention to
cheeks laterally. Labial glands are present in the mucosa and affect the height of the vestibule is the so-called Rehrmann’s
produce fluid that empties through small ducts in the vesti- flap (Figs. 3.6 and 3.7), a technique of surgical closure of an
bule keeping it moist. Similarly, the vestibule receives the oroantral communication (OAC) using a vestibular-based
orifice of the parotid duct. The dental arches including the mucoperiosteal flap (Batra et al. 2010). The depth of the ves-
alveolar processes with the teeth mark the internal boundary tibule is markedly reduced when a periosteal incision is per-
of the vestibule. The vestibule is highly dynamic and con- formed to mobilize and reposition the flap over the alveolar
stantly changing size and shape during jaw movements, mas- ridge to the palatal aspect of the OAC (Figs. 3.8, 3.9, and
tication, and activation of perioral facial muscles. 3.10).
The depth and the width of the vestibule are dependent on The frenulum (l, little bridle) is a prominent anatomical
the adjacent anatomical structures and vary with age. In chil- structure that forms a thin mucosal reflection traversing the
dren, the vestibule is shallow, but gradually increases in vestibule. Two frenula are identified along the maxillary and
height during the eruption of the permanent teeth. After mandibular midline including the frenulum labii superioris
removal or loss of teeth, the bone of the alveolar process and frenulum labii inferioris, but additional variants may
undergoes vertical and horizontal resorption (Schropp et al. also occur in the posterior areas of the vestibular sulcus
2003; Covani et al. 2011; Tan et al. 2012; Pietrokovski 2013). (Figs. 3.11, 3.12, 3.13, 3.14, and 3.15). The frenula typically
As a consequence, alterations in hard tissue spatial relation- enclose muscle fibers usually originating from the orbicu-
ships may decrease the depth of the vestibular sulcus. These laris oris muscle. These mucosal reflections attach the lips
changes have clinical and esthetic implications during dental and cheeks externally to the alveolar mucosa and underlying
rehabilitation. A reduced vestibular depth may compromise periosteum internally (Priyanka et al. 2013).
the seal of full dentures, limit the length of the vestibular A recent systematic review of the literature found that the
shelf of removable prostheses, and increase the risk of muco- maxillary midline labial frenulum (MMLF) is associated
sal irritations. A clinical study on the location of traumatic with numerous syndromes and plays a role in the develop-
ulcerations following placement of complete dentures ment of the maxillary central diastema. However, it remains
showed that denture-induced irritations appeared most often unclear whether the frenulum contributes to gingival reces-
in the vestibular sulcus (Kivovics et al. 2007). Since most sion or peri-implant mucosal disease (Delli et al. 2013). A
mucosal injuries are located in the vestibule, adequate exten- new clinical study demonstrated that the MMLF may present
sion of denture flanges, especially during border molding, morphologic variations such as nodules, mainly found in the
and use of pressure indicators that reveal overextended bor- intermediate third of the frenulum, or appendices, commonly
ders are recommended to reduce the risk of mucosal injuries seen in the labial third of the frenulum (Townsend et al.
and to improve patient comfort following complete denture 2013). The authors determined that variations of the MMLF
placement (Sadr et al. 2011). are inherent and do not represent a pathologic condition, nor
A shallow vestibule is normally associated with reduced do they require biopsy for diagnostic purposes.
esthetics due to loss of occlusal height resulting in a so- Another study assessed the level of MMLF attachment in
called dish face. Often the loss of hard tissue height is com- children of 1–18 years of age (Boutsi and Tatakis 2011).
upper
vestibule
lower
parotid vestibule
papilla lower lower
vestibule vestibule
Fig. 3.1 Illustration of the left posterior upper and lower vestibules
upper upper
vestibule vestibule
Fig. 3.6 Illustration of an oroantral communication (OAC) in the dis- Fig. 3.7 Illustration of OAC closure using a buccal flap that was
tobuccal alveolus (arrow) of the right maxillary first molar advanced to the palatal aspect of the alveolus following periosteal inci-
sion (Rehrmann technique)
Fig. 3.9 Surgical closure with a mobilized vestibular mucoperiosteal Fig. 3.12 Occlusal view of the labial frenulum (arrowhead) joining
flap (Rehrmann technique) with the incisal gingiva (*) and continuing to the palatal surface cours-
ing between the two central incisors
Fig. 3.10 Two months after surgery, the healed site shows a typical Fig. 3.13 Thin labial frenulum (arrow) at the midline with a mucosal
flattening of the vestibule nodule (asterisk) in a 76-year-old male; a fistula is also present
(arrowhead)
Fig. 3.11 Prominent labial midline frenulum (arrowhead) in a 15-year- Fig. 3.14 Double buccal frenulum (arrows) located above the right
old boy with the left central incisor displaying hypoplastic enamel maxillary first premolar (44-year-old female)
(arrows) due to trauma to its predecessor
3 Vestibule and Cheeks 19
zygomatic
infraorbital
parotid-
masseteric
buccal
20 3 Vestibule and Cheeks
MeN
OO
BM
OO
The buccinator contributes, along with other perioral its posterosuperior portion by the parotid duct (Fig. 3.20),
facial muscles, to the formation of the modiolus, a small, terminating at the parotid papilla in the mucosa of the cheek
button-shaped node of connective tissue slightly lateral to the opposite the maxillary first or second molars (Fig. 3.21). The
labial commissure (Chap. 2). The buccinator is perforated in location of the parotid duct orifice was examined by Suzuki
3 Vestibule and Cheeks 21
OO
BM
1
4 OO
PD
*
masseter muscle BM
DAO
et al. (2009). They made a 2 mm hole at the center of an tooth surfaces and mucosa around the agent was taken with
adhesive therapeutic agent for aphthous stomatitis and placed the teeth in centric occlusion. The mean location of the
the agent on the mucosa so that the hole matched the parotid parotid duct orifice was 0.4 mm mesial to the contact surface
duct orifice. To locate the orifice, an impression of the buccal between the maxillary first and second molars (range 7.5 mm
22 3 Vestibule and Cheeks
orbicularis oris
buccinator
orbicularis oris
mentalis
BFP
LAO
BMup
parotid
gland
BMlp
OO
MeN
In a retrospective study with 161 patients, the buccal fat all patients were free of pain or any limitations after the
pad was successfully used in 92.5 % for closure of an OAC 6-month follow-up period (Poeschl et al. 2009). In another
(Poeschl et al. 2009). Excluding all severe and complicat- study with 75 patients (23 with chronic oroantral fistula),
ing cases such as tumor-related defects or previously the 6-month follow-up revealed uneventful healing in all
treated cases, the overall success rate for closure of the patients following closure of OAC with a pedicled buccal
OAC was nearly 98 %. No late complications occurred, and fat pad (Dolanmaz et al. 2004). Though partial necrosis of
24 3 Vestibule and Cheeks
PSAN ION
MSAN
ASAN
SL
LBN
IAN
MeN
the flap was observed in three patients, this did not affect type II pattern displayed two twigs passing through a buccal
the final healing. extension of the buccal fat pad (26.3 %). An interrelation of
Because of its favorable anatomic location, high vascular- the parotid duct and the buccal fat pad was also observed.
ity, ease of handling, and low failure rate, the buccal fat pad One pattern consisted of the parotid duct crossing superficial
has become the flap of choice for reconstruction of various to the buccal extension of the buccal fat pad in 42.1 % of the
oral defects including oral malignancies, treatment of pri- cases while it crossed along the superior border of the buccal
mary clefts, and coverage of mucosal defects (Rapidis et al. extension of the buccal fat pad in 31.6 % and crossing deep
2000; Singh et al. 2010; Gröbe et al. 2011). The pedicled to the buccal extension of the buccal fat pad in 26.3 %, pos-
buccal fat pad is further distinguished by the minimal mor- ing a risk to the parotid duct. Accordingly, there is a 26.3 %
bidity of the donor site without esthetic or significant func- chance of injury to the buccal branch and similarly to the
tional impairment (Gröbe et al. 2011). On the other hand, parotid duct during total removal of the buccal fat pad
some authors have warned that the buccal branches of the (Hwang et al. 2005).
facial nerve or the parotid duct are vulnerable during manip- Neural sensory supply to the vestibular sulcus and to the
ulation of the buccal fat pad (Hwang et al. 2005). cheek is provided by branches originating from the maxillary
In a study with 19 cadaveric hemifaces, the buccal and mandibular divisions of the trigeminal nerve (CN V)
branches of the facial nerve had two locations at the buccal (Fig. 3.24). In the upper jaw, the anterior vestibular sulcus is
fat pad (Hwang et al. 2005). For type I pattern, branches supplied by the superior labial branch from the infraorbital
crossed superficial to the buccal fat pad (73.7 %), while the nerve and by the anterior superior alveolar nerve that
3 Vestibule and Cheeks 25
AN SLA
BA
ECA
IAA
ILA
FA
FA
Me A
ECA
CCA
Clinical Relevance of the Vestibule Vestibular frenula may be used to hide scars of vertical
and Cheeks releasing incisions; hence, the clinician is advised to thor-
oughly diagnose their location and extent before choosing
The vestibule provides access to the lateral, i.e., labial and specific flap designs. Prominent maxillary midline frenula are
buccal, aspects of the teeth and jaws. The vestibule is the often removed before implant placement, or at reentry sur-
most common site for dental infection and often requires gery, to improve the esthetics or soft tissue spatial relation-
drainage intervention from a vestibular approach to pre- ships around dental implants in the esthetic maxillary zone.
vent spread. The depth and width of the vestibule highly The buccinator muscle is the critical anatomical structure
correlates with the presence or absence of the teeth and the in the cheek. Dental infections spreading to the medial side
alveolar process. For example, the parotid papilla may of the buccinator will lead to induration or swelling of the
become located dangerously close to the alveolar crest in vestibular aspect of the cheek that is usually only visible
an edentulous and atrophic maxilla. As a consequence, the intraorally. In contrast, maxillary infections extending above
surgeon must avoid placing incisions close to the parotid the buccinator to the cheek produce an extraoral swelling lat-
duct and papilla in the maxillary vestibule. In the same eral to this muscle of the cheek. Drainage requires an extra-
region, deep incisions may invade the Bichat’s fad pad that oral incision of the skin overlying the abscess. Such an
suddenly and unexpectedly will protrude into the incision should be placed parallel to the parotid duct and the
vestibule. buccal branch of the facial nerve.
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Parotid Glands
4
The parotid gland is characterized as a compound tubuloal- larly (see also Fig. 3.20). The parotid duct enters the oral
veolar gland. It is the largest of the salivary glands that, as a cavity on the buccal mucosa opposite the first or second
group, also include the submandibular and sublingual glands maxillary molar (Figs. 4.4, 4.5, and 4.6) (Chap. 3).
as well as numerous small glands in the mucosa of the oral An ultrasound study in 50 healthy adults identified a bilat-
cavity. The parotid gland is located in the interval between eral parotid duct in all participants with one subject present-
the sternocleidomastoid muscle and mandible extending ing a double duct on both sides (Stringer et al. 2012). The
from the posterior part of the zygomatic arch to the outer mean maximum internal caliber was 0.6 ± 0.2 mm, and the
mandibular angle in the vertical direction (Figs. 4.1 and 4.2). mean length was 42 ± 7.5 mm. In 93 % of individuals, the
In the horizontal plane, the gland reaches from the subcuta- duct was within 1.5 cm of the middle half of a line between
neous fat tissue beyond the posterior border of the mandibu- the lower border of the tragus and cheilion. Another study
lar ramus to the infratemporal region. The parotid gland is using sialographic morphometry of 43 parotid ducts yielded
positioned inferior to the zygomatic arch and mostly superfi- a mean duct length of 50 mm (Horsburgh and Massoud
cial and posterior to the masseter muscle. The parotid gland 2013). The mean widths of the proximal, middle, and distal
lies anterior to the ear and mastoid process and inferior to the segments of the parotid duct were 1.8 mm, 1.1 mm, and
external auditory meatus and external ear. Its inferior tip, or 1.6 mm, respectively.
apex, extends inferior to the ear and to the area of the man- In a histological study assessing the diameter of 25 parotid
dibular ramus and angle. The parotid gland is encapsulated ducts while accounting for a formalin-induced shrinkage
in a thick connective tissue fascia, called the parotid fascia. It factor, the mean diameter ranged between 0.5 and 1.4 mm
is derived from fascia covering the masseter muscle combin- (minimum 0.1 mm, maximum 2.3 mm), depending on the
ing with the deep cervical fascia of the neck serving to sepa- site (Zenk et al. 1998). In all preparations, the minimum
rate it from the submandibular gland. width of the secretory duct was located at the ostium, but a
The parotid gland is shaped approximately as an inverted narrowing at the middle of the duct was striking. In a study
triangle with the apex between the sternocleidomastoid mus- with 29 fresh cadaveric halves, the relationship of the parotid
cle and the mandibular ramus. The base roughly follows the duct to the facial nerve was evaluated (Richards et al. 2004).
zygomatic arch. The lateral surface is covered by skin, but The facial nerve and its branches were always observed lat-
also includes small lymph nodes embedded in the gland. The eral to the parotid duct. Because surgical dissection is per-
mandible grooves the anterior border. The parotid gland is formed lateral to the facial nerve during a superficial
largely separated into superficial and deep components by parotidectomy, the parotid duct remains usually intact
the plexus of the facial nerve (Fig. 4.3). The superficial com- (Richards et al. 2004).
ponent frequently displays a loosely attached portion called Observations from 96 dissections of human parotid glands
the accessory parotid gland. The parotid duct also called revealed in 21 % a clearly detached accessory gland at vari-
Stensen’s duct and named after Niels Stensen, 1638–1686, able distances from the main gland (Frommer 1977). In a
who was a Danish anatomist and geologist, serves as the sialographic study, an accessory parotid gland was observed
secretory channel that emerges from the superficial compo- in 68 % of patients with a mean angle of 53° at the conflu-
nent of the gland. The duct emerges from the anterior border ence of its tributary duct with the parotid duct (Horsburgh
of the gland approximately 1 cm below the zygomatic arch, and Massoud 2013). Accessory parotid tissue may also be
extends anteriorly and crosses the masseter on the outer sur- found in rare cases with uni- or bilateral aplasia of the parotid
face curving sharply to perforate the buccinator perpendicu- glands (Goldenberg et al. 2000; Antoniades et al. 2006).
TM
ZA
EAC PD
PG
BM
MM
SCM
PD
PG
BM
masseter
muscle
4 Parotid Glands 31
SCM
buccinator
muscle
PD
PP
MM1
MM2
Fig. 4.4 Illustration of the parotid duct perforating the buccinator mus-
cle and entering the oral cavity opposite the junction between first and
second maxillary molars (inferior view of right maxilla). MM1 masse-
ter muscle (middle layer), MM2 masseter muscle (deep layer), PD
parotid duct, PP parotid papilla
Fig. 4.5 Clinical view of the right buccal plane showing a typically
round parotid papilla (arrow) in a 68-year-old female
32 4 Parotid Glands
Facial Nerve
FNt
FNz
PG
FN 1 FNb
FNm
FNc
FNm
FNc
Facial Nerve 35
FNz
FNb
ZMa
PG
PD
MM FV
PG
FA
FNm
Fig. 4.10 Dissection of the right side of a cadaveric head showing the lar branch), FNz facial nerve (zygomatic branch), FV facial vein, PD
parotid gland and some branches of the facial nerve. FA facial artery, parotid duct, PG parotid gland, MM masseter muscle, ZMa zygomati-
FNb facial nerve (buccal branch), FNm facial nerve (marginal mandibu- cus major muscle
FNz
FNz ZMa
FNb ZMa
PD
PG
PD FV
FA
PG
MM
Fig. 4.11 Magnification of the zygomatic and buccal branches of the vein, MM masseter muscle, PD parotid duct, PG parotid gland, ZMa
facial nerve and contiguous structures. FA facial artery, FNb facial zygomaticus major muscle
nerve (buccal branch), FNz facial nerve (zygomatic branch), FV facial
36 4 Parotid Glands
PD
MM
FV
FA
PG
FA
FNm
FNm
Fig. 4.12 Magnification of the marginal mandibular branch of the facial nerve and contiguous structures. FA facial artery, FNm facial nerve (mar-
ginal mandibular branch), FV facial vein, MM masseter muscle, PD parotid duct, PG parotid gland
Auriculotemporal Nerve
ON
TGG
MX
MN
STA
MMA
MN
ATN
ATN
MA
IAN LN
MA
ECA
MN LBN
ATN
ATN
IAN
LN
IAN MPM
LN LBN
Fig. 4.16 Deep dissection of the right cadaveric infratemporal fossa inferior alveolar nerve, LBN long buccal nerve, LN lingual nerve, MN
with the zygomatic arch and relevant vasculature removed showing the mandibular nerve, MPM medial pterygoid muscle
roots of the auriculotemporal nerve. ATN auriculotemporal nerve, IAN
External Carotid Artery 39
External Carotid Artery Within the parotid gland, the ECA lies deep to the facial nerve
within the medial portion of the gland, and it divides into its
The external carotid artery (ECA) arises from the common terminal branches, the superficial temporal and maxillary
carotid artery along with the internal carotid artery (Figs. 4.17, arteries. The superficial temporal artery gives rise to the trans-
4.18, and 4.19). The ECA ascends in a slight curve toward the verse facial artery that accompanies the parotid duct through
parotid gland. It is crossed by the hypoglossal nerve, by the the superficial component of the gland. The superficial tempo-
posterior belly of the digastric muscle, and by the stylohyoid ral artery then exits the base of the gland. The maxillary artery
muscle. As it enters through the posterior border of the parotid courses through the deep lobe of the parotid gland and runs
gland, the ECA gives rise to the posterior auricular artery. toward the pterygomaxillary fissure (Chap. 11).
STA
OA PAA MA
APA
FA
LA
ICA
ECA STh
CCA
Fig. 4.17 Illustration of the branches of the external carotid artery carotid artery, LA lingual artery, MA maxillary artery, OA occipital
(right side of skull). APA ascending pharyngeal artery, CCA common artery, PAA posterior auricular artery, STA superficial temporal artery,
carotid artery, ECA external carotid artery, FA facial artery, ICA internal STh superior thyroid artery
40 4 Parotid Glands
STA
MN
TFA
STA MMA
STA MA
MA
STA
MA
PAA LN
IAN
PG
OA
ECA IAA
MtA
FA
ICA FA
ECA SMA
FA
CCA
Fig. 4.18 Dissection of primary branches of the right external carotid Fig. 4.19 Deep dissection of right cadaveric infratemporal region
artery and selected secondary branches. CCA common carotid artery, demonstrating the bifurcation of the external carotid artery into the
ECA external carotid artery, FA facial artery, ICA internal carotid artery, maxillary and superficial temporal arteries. Note that the mandibular
MA maxillary artery, MtA masseteric artery, OA occipital artery, PAA ramus and zygomatic arch have been resected and the masseter muscle
posterior auricular artery, SMA submental artery, STA superficial tem- has been reflected. ECA external carotid artery, IAA inferior alveolar
poral artery, TFA transverse facial artery artery, IAN inferior alveolar nerve, LN lingual nerve, MA maxillary
artery, MMA middle meningeal artery, MN mandibular nerve, PG
parotid gland, STA superficial temporal artery
Retromandibular Vein 41
Retromandibular Vein an upper and lower ring, through which the superior and
inferior divisions of the facial nerve passed (Alzahrani and
The retromandibular vein (RMV, also termed temporomax- Alqahtani 2012). The RMV gives rise to the external jugular
illary vein or posterior facial vein) (Figs. 4.20, 4.21, and vein near the apex of the parotid gland where it exits to
4.22) is used as a guide to expose the facial nerve branches anastomose with the facial vein (Cvetko 2015). However,
inside the parotid gland, during parotid surgery and open the course of the RMV and its anastomoses are notoriously
reduction of mandibular condyle fractures (Piagkou et al. variable, and the anterior division of the RMV can com-
2013). The RMV forms by the union of the superficial tem- monly join the facial vein, while the posterior division joins
poral and maxillary veins. The RMV courses downward the posterior auricular vein forming the external jugular
through the parotid gland. Within the parotid gland, the vein (Piagkou et al. 2013). Despite of its variability, the
RMV is usually located medial to the facial nerve but lateral RMV was located 5.5–8.6 mm posterior and 4.2–9.1 mm
to the external carotid artery (Fig. 4.3) (Toure and Vacher medial to the posterior border of the mandible in a Korean
2010). In an unusual case report, the RMV presented with sample (Hwang et al. 2009).
OpVs
AV
OpVi
STV
IOV
PVP
MV FV
IJV
RMV
FV
EJV
IJV
Fig. 4.20 Illustration of the retromandibular vein and surrounding inferior ophthalmic vein, OpVs superior ophthalmic vein, PVP ptery-
veins. AV angular vein, EJV external jugular vein, IJV internal jugular goid venous plexus, RMV retromandibular vein, STV superficial tempo-
vein, IOV infraorbital vein, FV facial vein, MV maxillary vein, OpVi ral vein
42 4 Parotid Glands
PD
PG
MM
FV RMV
FA
SCM
SMV
EJV
IJV
SMG
Fig. 4.21 Dissection of the left cadaveric parotid region showing the jugular vein, PD parotid duct, PG parotid gland, MM masseter muscle,
large veins and contiguous structures associated with the parotid gland. RMV retromandibular vein, SCM sternocleidomastoid muscle, SMG
EJV external jugular vein, FA facial artery, FV facial vein, IJV internal submandibular gland, SMV submental vein
PD
FV
PG
RMV
MM
FA
EJV FV
IJV
SMV
Fig. 4.22 Dissection of the right side of a cadaveric head demonstrat- parotid duct, PG parotid gland (superficial part has been resected), MM
ing the large veins associated with the parotid gland. EJV external jugu- masseter muscle, RMV retromandibular vein, SMV submental vein
lar vein, FA facial artery, FV facial vein, IJV internal jugular vein, PD
Clinical Relevance of the Parotid Gland and the Facial Nerve 43
Clinical Relevance of the Parotid Gland lel to the medial aspect of the ramus, the tip of the cannula
and the Facial Nerve may reach the retromandibular area, and the bolus is depos-
ited posterior to the ramus instead of to the mandibular fora-
For the dental practitioner, knowledge of the anatomical men that is the intended target. Two forms of facial paralysis
aspects of the parotid gland and the facial nerve is helpful for (Bell’s palsy) have been described (Chevalier et al. 2010).
the following reasons: The first, an acute form, has an immediate onset after the
administration of the local anesthesia. When the anesthesia
• Differentiation of retromandibular swellings subsides, the facial paralysis also disappears. The cannula
• Facial paralysis (Bell’s palsy) following mandibular block has either perforated the capsule of the parotid gland with
anesthesia injection of the local anesthetic close to the facial nerve, or
the facial nerve has an aberrant course in the retromandibular
A patient with a retromandibular swelling may first con- space, and it is directly anesthetized by the misdirected can-
sult a dentist since this finding is suspected to be associated nula. The second, a delayed form of Bell’s palsy, commences
with a tooth. Apart from a thorough clinical and radiographic hours or days after the administration of the mandibular
examination, two extraoral signs indicate that the parotid block anesthesia and may last for days to weeks. Two hypoth-
gland may be the cause of the swelling (Figs. 4.23 and 4.24): eses have been suggested to cause the delayed form (Tiwari
(1) the posterior border and angle of the ramus are no longer and Keane 1970; Shuaib and Lee 1990; Tazi et al. 2003;
palpable, compared with the contralateral side, and (2) the Chevalier et al. 2010): (1) ischemia of the facial nerve fol-
swelling has elevated the earlobe laterally and superiorly lowing reflex angiospasm of the stylomastoid artery and (2)
compared with the contralateral side. reactivation of latent herpes simplex viruses (HSV-1) or vari-
The inadvertent anesthesia of the facial nerve is an occa- cella zoster viruses (VZV) by the local anesthesia with an
sional finding following mandibular block anesthesia ascending infection of the facial nerve (Furuta et al. 1998,
(Figs. 4.25 and 4.26). If the direction of the syringe is paral- et al. 2000).
Fig. 4.23 Typical location of a swelling associated with the left parotid
gland (*) in a 65-year-old male. Note that the left mandibular angle is
no longer visible or palpable and that the left earlobe is lifted laterally
IAN
PG
MF
La
PG
Fig. 4.26 Bell’s palsy on the left side of a 34-year-old female follow-
ing ipsilateral inferior alveolar block anesthesia. Note that the patient
cannot close her left eye and that the lips move to the right side when
the patient purses her lips
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Anterior Maxilla
5
The anterior maxilla (Fig. 5.1) is a clinically critical area crest provides an anatomical boundary that corresponds to
frequently requiring extensive surgical interventions, e.g., what clinicians often call the “esthetic zone” extending bilat-
placement of dental implants, surgical removal of impacted erally between premolars perpendicular to the dental arch
or supernumerary teeth, periodontal surgery, endodontic sur- and from the alveolar crest to the nasal aperture in the verti-
gery, cyst therapy (Figs. 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, and cal dimension. Thus, the anterior maxilla must be carefully
5.9), and orthognathic surgery. This is particularly true considered to achieve optimal esthetic treatment outcomes.
regarding treatment of edentulous or partially dentate The surface of the anterior maxilla contributes to the
patients that were previously rehabilitated with mucosa- or nose and, inferiorly, the primary palate. The region is char-
tooth-borne prostheses; however, the focus has shifted to acterized by a prominent intermaxillary suture establishing
implant-borne reconstructions in the last three decades a midline articulation between the maxillary bones (os max-
(Belser et al. 2000; Pjetursson et al. 2007) (Figs. 5.10, 5.11, illae). It is observed on the facial aspect in dry skulls extend-
5.12, 5.13, and 5.14). Thus, increased demand for endosse- ing from the anterior nasal spine toward the interdental bone
ous implants in dentistry has necessitated a greater apprecia- between the two central incisors and eventually reaching the
tion and understanding of surgical techniques that in turn alveolar crest (Fig. 5.19). This bony suture is visible on
require a firm understanding of the anatomy of the anterior standard periapical or occlusal radiographs (Figs. 5.20 and
maxilla (von Arx et al. 2013). 5.21).
The maxillary bone (Fig. 5.15) supports the upper teeth The anterior maxillary surface also contributes to the
and contributes the majority of the facial skeleton. It com- lower margin of the nasal aperture (apertura piriformis due to
prises a body that is pyramidal in shape with the base border- its pear-like appearance) (Figs. 5.22 and 5.23) (Moreddu
ing the nasal cavity and the apex bordering the zygomatic et al. 2013). The proximity of the nasal cavity must be con-
bone. The maxillary body can be described as possessing sidered when performing surgery in the anterior maxilla
four processes including the frontal, zygomatic, palatine, and (Figs. 5.24, 5.25, 5.26, 5.27, 5.28, and 5.29). Given the high
alveolar processes (Figs. 5.16 and 5.17). The frontal process number of dental implants inserted in the anterior maxilla,
extends superiorly and is positioned between the nasal bone the occurrence of nasal floor penetration is relatively rare
anteriorly and the lacrimal bone posteriorly. The zygomatic (Figs. 5.30, 5.31, 5.32, and 5.33). A report described an
process projects laterally and articulates with the zygomatic unusual case of recurrent rhinosinusitis following implant
bone. The palatine process extends medially and articulates placement in the maxilla (Raghoebar et al. 2004). The
with its partner at the midline through the intermaxillary 69-year-old female patient complained of intermittent nasal
suture. The alveolar process extends inferiorly from the max- congestion, rhinorrhea, and crustae in the right nasal cavity
illary body and supports the alveolar sockets and teeth. The and infrequent headache with dullness in the paranasal
maxillary body is also characterized by four surfaces includ- region. Naso-endoscopic examination confirmed that two
ing the anterior (facial), posterior (infratemporal), medial implants were extending into the right nasal cavity. The nasal
(nasal), and superior (orbital), all of which possess unique mucosa was incised and elevated, and both implants were
features necessary for presurgical consideration. resected to the level of the nasal bone. Healing was unevent-
The jugal crest (zygomaticoalveolar ridge) is a prominent ful and previous symptoms completely disappeared. The
feature on the anterior surface running from the zygomatic authors concluded that the perforating implants might have
process to the first molar serving as an anatomical landmark altered the nasal airflow inducing irritation of the nasal
separating the anterior (facial) portion of the maxilla from its mucosa, mucous secretion, and crust formation, eventually
posterior (infratemporal) portion (Fig. 5.18). This osseous resulting in rhinitis (Raghoebar et al. 2004).
Fig. 5.4 The enucleated tissue with histopathology consisting of an Fig. 5.6 After filling the bone defect with collagen fleece, the access
odontogenic cyst of inflammatory origin or radicular cyst window is covered with a collagen membrane to prevent the ingrowth
of soft tissue
Fig. 5.5 The apex of the central incisor is resected and retrofilled. In Fig. 5.7 Primary wound closure is accomplished with multiple, single
addition, a collagen membrane is placed on the exposed palatal mucosa interrupted sutures. Note the site of the fistula (sinus tract) in the api-
(through-and-through lesion) covestibular area of the left central incisor (arrow)
50 5 Anterior Maxilla
Fig. 5.8 Clinical picture 5 years after surgery Fig. 5.10 Frontal view of the teeth of a 21-year-old female who suffers
from a generalized dentinogenesis imperfecta characterized by teeth
that exhibit a typically opalescent color
the labial and lingual cortex in the anterior maxilla follow- respectively, and in edentulous samples 1.0 ± 0.29 mm and
ing tooth extractions in dentate samples and following a 1.4 ± 0.45 mm, respectively.
3.0 mm reduction of crest height in edentulous samples. The A cadaver study evaluated the thickness of the labial bone
mean thickness of the labial and lingual bone plates in den- plates of anterior teeth following reflection of the soft tissues
tate samples measured 1.6 ± 0.71 mm and 2.0 ± 0.70 mm, and removal of the bone (Han and Jung 2011). At the crest
52 5 Anterior Maxilla
OMf
OFm
OMz OMp
OMa OMa
Fig. 5.15 Illustration of the maxillary bone (highlighted) with its fron- maxilla, OMf frontal process of os maxilla, OMp palatine process of os
tal, zygomatic, palatine, and alveolar processes labeled in the right os maxilla, OMz zygomatic process of os maxilla
maxilla. OFm medial part of orbital floor, OMa alveolar process of os
level, the mean width of the labial bone plate was facial bone plate thickness from the first premolars to the
0.97 ± 0.18 mm, 0.78 ± 0.21 mm, and 0.95 ± 0.35 mm for cen- central incisors. The mean radiographic thickness of the
tral incisors, lateral incisors, and canines, respectively. facial bone wall for all examined teeth (n = 498) was 0.5 mm
Recently, several studies have evaluated the width of the (range 0–2.1 mm) assessed at 4 mm apical to the cementoe-
labial bone plates using CBCT (Fig. 5.46). One study evalu- namel junction (CEJ), and measured at the middle of the root
ated the thickness of the facial bone plate in the anterior it was 0.6 mm (range 0–2.8 mm).
maxilla in 125 patients (mean age 47.3 years) with CBCT In a similar study evaluating CBCT images of 43 patients
(Braut et al. 2011). The facial bone wall in the crestal area scheduled for implant treatment, the bone thickness was
was found to be either missing or thin in about 90 % of the determined in maxillary anterior teeth and premolars at three
patients. There was a statistically significant decrease in different levels: at 1 mm apical to the alveolar bone level, at
5 Anterior Maxilla 53
OMf
OFm
OMp
Ci
OMa
OMz
Fig. 5.16 Anterosuperolateral view of the left os maxilla (Beauchene of os maxilla, OMp palatine process of os maxilla, OMz zygomatic pro-
skull model). Ci impacted left maxillary canine, OFm medial part of cess of os maxilla
orbital floor, OMa alveolar process of os maxilla, OMf frontal process
OMf
LNW
OP
OMp
OMa
Fig. 5.17 Medial view of the left os maxilla (Beauchene skull model). LNW lateral nasal wall, OMa alveolar process of os maxilla, OMf frontal
process of os maxilla, OMp palatine process of os maxilla, OP os palatinum
the mid-root level, and at 1 mm from the tooth apex (Vera The finding of a predominantly thin facial bone plate
et al. 2012). The median width of the facial bone for anterior superficial to the six maxillary anterior teeth was also con-
teeth was 0.83 mm, 0.70 mm, and 0.88 mm, respectively, at firmed in a CT study of randomly selected 66 patients
the three levels; in the premolar area, the median measure- (mean age 39.9 years) with an intact anterior maxilla
ments were 1.13 mm, 1.03 mm, and 0.88 mm, respectively. (Ghassemian et al. 2012). The average bone thickness at
54 5 Anterior Maxilla
ZMS IOF
CR
CR
IMS
3 mm from the CEJ for the maxillary right central incisor facial bone thickness averaged 1.47 and 1.60 mm, respec-
was 1.41 mm and for the maxillary left central incisor was tively (Ghassemian et al. 2012). A clinical and radiographic
1.45 mm. For the maxillary right and left lateral incisors, (CBCT) examination of 60 healthy subjects showed that
the facial bone thickness averaged 1.73 and 1.59 mm, the width of the labial bone plate in the anterior maxilla
respectively. For the maxillary right and left canines, the (canine to canine) is correlated with the clinical periodontal
5 Anterior Maxilla 55
Fig. 5.20 Periapical radiograph showing the intermaxillary suture non-ankylosed tooth. As a consequence, removal of the
(arrows) in a 9-year-old girl in whom the left central incisor has been
root canal treated following trauma
tooth will result in considerable bone resorption and reduc-
tion of approximately 2–3 mm of the facial aspect of the
alveolar ridge (Figs. 5.48 and 5.49) (Araujo et al. 2005;
biotype (Cook et al. 2011). A thin biotype was significantly Nevins et al. 2006).
associated with a thinner bone plate (canine 0.28 mm, lat- Prominent features of the anterior maxilla are ridges
eral incisor 0.37 mm, central incisor 0.38 mm; measure- formed by the tooth roots. The canine eminence overlies
ments taken 4 mm apical to CEJ) compared to a thick the root of the canine separating the anterior maxilla into
biotype (canine 0.66 mm, lateral incisor 0.79 mm, central two concave areas including a shallow incisive fossa ante-
incisor 0.81 mm) (Cook et al. 2011). riorly and a deeper canine fossa posteriorly (du Toit and
Facial bone height and thickness was quantitatively Nortje 2003) (Figs. 5.50 and 5.51). The canine fossa is
assessed with high precision and accuracy utilizing CBCT positioned superior and lateral to the apex of the canine
based on a study comparing standardized CBCT slices tooth and lateral to the nasal aperture. The cortical bone in
with direct measurements of 65 embalmed cadaveric this area is an ideal area for harvesting bone chips for peri-
heads (Timock et al. 2011). The mean absolute differ- implant bone and contour augmentation. An edentulous
ences were 0.30 mm in facial bone height and 0.13 mm in maxilla may increase the prominence of one or both fossae
facial bone thickness with no pattern of over- or resulting in what may appear radiographically as a well-
underestimation. defined radiolucency reminiscent of a cyst or a ground-
In summary, a thin facial bone wall prevails in the ante- glass pattern similar to fibro-osseous disease (Giunta 2002)
rior maxilla, and in general the facial bone wall thickness (Figs. 5.52, 5.53, and 5.54). Anterior labial concavities
decreases from premolars to anterior teeth (Wang et al. are palpable and are often visualized as an indentation in
2014) (Fig. 5.47). Histologically, this thin bone plate mainly the area of the observed radiolucency. Once the diagnosis
consists of bundle bone associated with the presence of a is made, typically no further treatment is suggested
56 5 Anterior Maxilla
LPE
LPE MS
MS NC
NC
IC IC
IC VO
IC
NFl
VO NC
NC
ANS
AMC
Fig. 5.23 Coronal CBCT scan of the midface showing the nasal cavity
in a 62-year-old male. IC inferior concha, LPE lamina perpendicularis
of ethmoid bone, MS maxillary sinus, NC nasal cavity, NFl nasal floor,
VO vomer
11 21
12 22
Fig. 5.25 Intraoral view showing a deep incision extending from the
canine to the central incisor
ANS
infundibulum
NPC
Fig. 5.33 A dry skull showing four dental implants supporting a full-arch fixed dental prosthesis. The implant on the far right side has slightly
perforated the bony floor of the nasal cavity (arrow). Macroscopically, a fine bony layer covers the apex of the implant
Several circumoral and nasal muscles of facial expression while the diminutive alar part originates from the incisive
take origin from the anterior maxilla and receive innervation fossa and travels superiorly inserting into the nasal ala. The
from the motor branch of the facial nerve (CN VII) (Chap. 2). depressor septi muscle also originates from the incisive fossa
The intrinsic muscles of the orbicularis oris take origin from and travels superiorly inserting into the nasal septum. The
the incisal region of the alveolar area of the anterior maxilla. insertion of these muscles is directly into the skin contrasting
The arrangement of these fibers is complex with some con- with most other muscles that are enveloped by a deep mem-
necting directly to the skin and mucous membrane while oth- branous fascia. Utilizing the bone to stabilize contraction,
ers pass outward to the angle of the mouth. Additional these muscles effectively achieve facial expression functions
intrinsic fibers arising from the anterior maxilla appear to and require special conservation during oral surgery.
cross at the midline and contribute to the formation of the The arterial supply to the bony structures and teeth of the
philtrum. The levator anguli oris muscle arises from the anterior maxilla is provided by the anterior and middle supe-
canine fossa and descends inserting into the skin of the angle rior alveolar arteries, branching from the infraorbital artery
of the mouth as well as interlacing with the intrinsic muscles within the infraorbital canal (Chap. 6). Vascularization of the
of the orbicularis oris. Similarly, deep fibers of the buccina- soft tissues such as the gingival and oral mucosa of the ante-
tors arise from the alveolar process of the anterior maxilla rior maxilla is achieved by the superior labial artery branch
and interdigitate with the orbicularis oris muscle as well as of facial artery and from terminal branches of the infraorbital
decussating and inserting into the upper and lower lips. The artery (Kleinheinz et al. 2005). The palatal process receives
levator labii superioris muscle takes origin from the anterior arterial supply from several sources (see also following
maxilla along the inferior border of the orbit passing inferi- chapters) including the nasopalatine and the greater palatine
orly to either insert directly into the skin overlying the lip or artery, but also from the anterior superior alveolar arteries
interlacing with the orbicularis oris. A portion of this muscle, traveling in separate small canals (accessory maxillary
the levator labii superioris alaeque nasi, arises from the fron- canals) to the anterior palate (Kleinheinz et al. 2005; von Arx
tal process of the anterior maxilla and passes inferiorly to et al. 2013).
insert into the skin overlying the alar cartilage of the nose as Venous drainage of the anterior maxilla occurs primarily
well as the skin and muscles of the lip. Nasal muscles of through the facial vein, although considerable variability
facial expression are also associated with the anterior max- occurs. The facial vein forms from its tributary, the angular
illa. The nasalis muscle typically shows two attachments to vein, along the medial corner of the eye. In this general area,
the anterior maxilla. The transverse portion arises from the the facial vein may form anastomoses with the superior and
region overlying the canine eminence and crosses bilaterally, inferior ophthalmic veins. The facial vein continues to
60 5 Anterior Maxilla
SCmc ANS
nasal floor
NPC
SC
SA
ANS
BFe
Fig. 5.37 Deep dissection of the anterior maxilla showing the anterior
nasal spine and cartilage of the nasal septum (the right half of the nose
is deflected laterally). ANS anterior nasal spine, BFe bone fenestration
over apex of right maxillary canine, SC septal cartilage of medial nasal
wall, SCmc mucosa of septal cartilage, SA right lower septal artery
62 5 Anterior Maxilla
nasal
aperture
ANS
Fig. 5.40 Intraoperative view of the surgical site for implant place-
ment in the maxillary left central incisor region in a 37-year-old female.
The bony ridge (arrow) leading to the anterior nasal spine is clearly
visible
CI LI C
Fig. 5.39 A 3D rendering of the CBCT images of the anterior nasal Fig. 5.41 A bone scraper is used for harvesting bone chips from the
spine. ANS anterior nasal spine, C canine, CI central incisor, LI lateral anterior nasal spine
incisor
10.6 13.1
mm mm
17.6 -
18.7 mm
Fig. 5.49 Following tooth extraction, the crestal portion of the thin
Fig. 5.48 Illustration of a typical alveolar bone configuration around a buccal plate has resorbed since it consists mainly of bundle bone
central maxillary incisor (buccolingual view) (arrows)
66 5 Anterior Maxilla
CFo
ANS
IFo
CR
CR
IFo
5 Anterior Maxilla 67
Fig. 5.54 The periapical radiograph of the right maxillary lateral inci-
sor confirms that there is no osseous lesion; hence, the radiolucency
seen in the panoramic radiograph corresponds to the incisor fossa
68 5 Anterior Maxilla
Clinical Relevance of the Anterior Maxilla microorganisms may enter the cranium by several pathways:
(1) direct extension along the fascial planes; (2) hematoge-
The anterior maxilla is of great clinical importance regarding nous spread along the facial (Figs. 5.55 and 5.56), angular,
facial esthetics (Chap. 2). A large proportion of dental implants ophthalmic, or other veins that lack valves, through the cav-
are inserted in the anterior maxilla to restore function and, ernous sinus into the cranium; (3) local lymphatics; and (4)
more importantly for many patients, to reestablish esthetics. extraoral odontogenic infection (Li et al. 1999). Dental
The majority of implant placement procedures in this region infections have occasionally been reported as the source of
requires additional peri-implant bone and contour augmenta- bacteria that can give rise to such a cerebral abscess (Schuman
tion due to the specific bone morphology of the facial bone and Turner 1994). A case report of cerebral abscess of odon-
plate with atrophic ridge alterations following tooth loss or togenic origin in a patient who presented multiple periapical
tooth extraction. A comprehensive understanding is required and periodontal lesions focused in the anterior maxilla, was
since bone defects and deficiencies result in reduced distances described by Mylonas et al. (2007). The treatment included
to adjacent anatomical structures. Therefore, collateral dam- immediate administration of high-dose intravenous antibiot-
age to contiguous structures such as the nasal cavity, nasopala- ics and craniotomy with resection of the abscess cavity.
tine canal/nerve/artery, and infraorbital foramen/nerve/artery Secondly, all decayed and periodontally as well as periapi-
can easily occur (see following chapters). cally involved teeth were removed to eradicate all possible
Another clinical aspect of the anterior maxilla refers to septic foci. Subsequently the patient made an uneventful
the risk of odontogenic infection spread to the cranium. Oral recovery (Mylonas et al. 2007).
PD
FA
FV
masseter
FA
Clinical Relevance of the Anterior Maxilla 69
CS OpVs
OpVi
IOV
PVP
FV
RMV
IAV
IJV
70 5 Anterior Maxilla
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Infraorbital Region
6
The infraorbital region is a component of the midface and region including closure of simple lacerations, biopsies,
can be defined as the anatomical area between the nasal aper- scar revisions, cosmetic cutaneous procedures, oral and
ture and the zygomatic bone below the inferior rim of the maxillofacial surgical interventions, and endoscopic maxil-
orbit and above the roots of the maxillary canine and premo- lary sinus surgery. The identification and preservation of
lars (Fig. 6.1). This area contains several clinically important the ION in maxillofacial trauma, although at times chal-
structures including the infraorbital foramen (IOF), the infra- lenging, are laudable goals. The most certain way to avoid
orbital nerve (ION) and artery (IOA), and their various damage to the ION is to understand the structures and spa-
branches to the adjacent anatomical structures. A very tial relationships in the region contiguous with the IOF
important albeit lesser known structure that is rarely men- (Cutright et al. 2003).
tioned in anatomical textbooks is the canalis sinuosus that The infraorbital space has been delineated as the area
has a unique tortuous course within the facial wall of the below the infraorbital foramen. The space is bounded by four
maxillary sinus region. facial muscles (Fig. 6.2), i.e., medially by the levator labii
Multiple fields of medicine operate in the infraorbital superioris alaeque nasi, laterally by the levator anguli oris, at
region including dentistry, dermatology, maxillofacial its superior margin by the origin of the levator labii superi-
surgery, ophthalmology, plastic surgery, and rhinology. The oris, and at its inferior margin by the orbicularis oris. The
neurovascular bundle of the IOF is therefore frequently infraorbital space is covered by the levator labii superioris
encountered in a host of procedures in the infraorbital muscle (Chap. 2) (Hu et al. 2006).
LLSAN
LLS
Infraorbital
space
LLSAN
LAO
LLS
OO
Infraorbital Canal coursing within the bone of the orbital floor. Haller’s cells
are associated with headache, chronic nasal obstruction, and
The so-called infraorbital groove-canal complex lies within mucoceles, increasing the risk of intraoperative complica-
the floor of the orbit. Mean distances for the groove-canal tions during endonasal procedures (Raina et al. 2012).
complex range from 25.4 to 31.9 mm (Table 6.1) (Figs. 6.3, In a radiographic study with three-dimensional recon-
6.4, and 6.5). The groove is also known as the infraorbital struction of high-resolution CT images obtained from 100
sulcus. Further anteriorly, the lateral edge extends over the patients, the mean angles of the IOC relative to the vertical
sulcus to create a roof, known as the orbital plate, resulting and horizontal planes were 13.2° ± 6.4° and 46.7° ± 7.6°,
in the infraorbital canal (IOC). As the IOC extends anteri- respectively (Hwang et al. 2013). The authors suggested that
orly, the orbital plate thickens to between 0.1 and 0.3 mm for neurotomy of the ION, the surgeon should guide the nee-
(Scarfe et al. 1998). The groove may be a canal over its entire dle through the IOF in the direction that is identical to the
length from the inferior orbital fissure to the IOF when com- axis of the IOC, i.e., 13.2° laterally and 46.7° cephalically.
pletely covered by bone. Scarfe et al. (1998) suggested that Also Lee et al. (2006) analyzed the angle of the IOC in 84
the IOC is represented by three different anatomical varia- sides of 42 dried skulls of Korean subjects. Three-dimensional
tions: canal only, groove only, and mixture of groove and models were created after obtaining CT data from the skulls.
canal. Others have proposed a classification of the canal- The mean angle of the IOC relative to the median plane was
groove complex using the proportion of the groove length to 12°, and the angle relative to the Frankfurt plane was 44°.
the total length of the groove-canal complex (Przygocka The mean angle between the IOC and the Frankfurt plane
et al. 2013). was 4° larger in males than in females.
A survey of 35 dry skulls (70 sides) found a complete roof The course of the IOC in the anterior part of the maxilla
of the canal in 57 % of the sides and a proximal groove and a (before leaving the IOF) was studied in axial CT scans of
distal canal in the remaining 43 % of specimens sampled 750 patients (Yenigun et al. 2016). In the majority of the
(Kazkayasi et al. 2001). A study assessing the symmetry of the cases (51.2 %), the IOC was located within the wall of the
length of the IOC in 100 dry skulls reported identically bilat- maxillary sinus or it was partially protruding into the maxil-
eral length in 65 %, whereas in 35 % the length of the right and lary sinus. In 12.3 % the IOC was totally protruding into the
left IOC differed by more than 0.5 mm (with asymmetry maxillary sinus, and in 36.4 % the IOC was coursing through
>2 mm in 3 % of the specimens) (Berge and Bergman 2001). the body of the os maxillae.
Two separate IOC with two distinct ION were described A study of 42 symmetrical, dry human skulls (late adoles-
in a case report by Leo et al. (1995). This rare case of the cence and adult) with no dental or skeletal anomalies demon-
ION bifurcating in the base of the orbit, and subsequently strated that the direction of the IOC in the frontal plane
emerging from two IOF separated from each other by 2 cm correlated with the transversal growth of the maxilla
in the axial plane and by 1 cm in the sagittal plane, was (Caspersen et al. 2009). A wide maxilla posteriorly resulted
detected during routine dissection of an embalmed adult in a small infraorbital transverse angle. The authors con-
Caucasian male cadaver. cluded that their findings might explain the different inclina-
An unusual course of the infraorbital nerve was described tion of ectopic canines.
by Chandra and Kennedy (2004). A 42-year-old male patient A study of 67 dry Indian skulls with regard to the angle of
with a 20-year history of chronic sinusitis was preoperatively the IOC reported an average angle of needle insertion of
assessed with CT. The right infraorbital nerve canal passed 21.1° ± 10.1° (range 4–52°) medial to the sagittal plane and
through the lumen of the maxillary sinus within the lamella of 31.8° ± 7.7° (range 14–56°) inferior to the Frankfurt plane
of an infraorbital ethmoid air cell (Haller’s cell) rather than (Aggarwal et al. 2015).
74 6 Infraorbital Region
SON
IFS
IOG
ZMS
IOC
IOF
Fig. 6.3 Anterior view of the
right midface in a dry skull
showing the infraorbital groove,
canal, and foramen. IFS inferior
orbital fissure, IOC infraorbital
canal, IOF infraorbital foramen,
IOG infraorbital groove, SON
supraorbital notch, ZMS
zygomaticomaxillary suture
Infraorbital Canal 75
orbit
IOG
orbit
IOG
IOC
MS
PPF
IOC Maxillary sinus
IOF
PPF
IOF Maxillary sinus
CSin
CSin
OMa
HP
Fig. 6.4 Infraorbital groove, canal, and foramen shown in a sagittal Fig. 6.5 Infraorbital groove, canal, and foramen depicted in a sagittal
CBCT image from a 62-year-old female (head slightly inclined to right CBCT image from a 53-year-old male. CSin double canalis sinuosus in
side). CSin canalis sinuosus in anterior wall of maxillary sinus, HP hard anterior wall of maxillary sinus. IOC infraorbital canal, IOF infraorbital
palate, IOC infraorbital canal, IOF infraorbital foramen, IOG infraor- foramen, IOG infraorbital groove, MS maxillary sinus, PPF pterygo-
bital groove, OMa alveolar process of os maxilla, PPF pterygopalatine palatine fossa
fossa
76 6 Infraorbital Region
IOF ZMS
ZMS IOF
IOF
Table 6.2 Location of the infraorbital foramen (IOF) in relation to the supraorbital notch/foramen (SOF)
Author(s) Study material N IOF medial to SOF % IOF coincident with SOF % IOF lateral to SOF %
Aziz et al. (2000) 47 cadaveric heads 94 sides 16.0 50.0 34.0
Chrcanovic et al. (2011) 80 adult dry skulls 160 sides 18.75 52.2 28.75
78 6 Infraorbital Region
IOF
PM2
Fig. 6.8 Lateral view of a dry skull depicting the location of the infra-
orbital foramen above second premolar. IOF infraorbital foramen, PM2
second premolar
Infraorbital Foramen 79
IOF
IOM
1/3
IOF 1/3
1/3
NVB
1/3
1/3
ALN
IOF 1/3
ALN
Table 6.3 Size (mm) of infraorbital foramen (IOF) and distances (mm) from IOF to neighboring anatomical structures
Distance
between
Distance between IOF and Distance between IOF
IOF and inferior facial and other anatomical
Author(s) Study material N Size of IOF orbital rim midline structures Comments
Aziz et al. 47 cadaveric 47 right Males: All: 8.3 Males: – *Mediolateral
(2000) heads sides *4.8 ± 1.0 Males: 8.5 ± 2.1 27.9 ± 4.9 width
Females: Females: 8.1 ± 1.6 Females:
*4.4 ± 1.0 25.5 ± 3.6
47 left Males: All: 8.1 Males: – *Mediolateral
sides *4.6 ± 1.2 Males: 8.5 ± 2.3 27.5 ± 3.7 width
Females: Females: 7.6 ± 1.6 Females:
*4.5 ± 1.0 26.9 ± 2.7
Berge and 100 dry skulls 198 sides 1
3.42 × 22.46 – – – Longest diameter
1
(2001) 2
1.67; max: 16
× 24)
Kazkayasi 35 adult dry 70 sides – 7.45 ± 0.95 (6–9.5) – Distance from IOF to All measurements
et al. skulls nasal aperture: were taken from
(2001) 17.2 ± 2.64 center of IOF
Distance from IOF to
canine bone crest:
35.0 ± 2.8 (30.5–39)
Distance from IOF to
foramen rotundum:
47.9 ± 5.53 (39.4–61.0)
Karakas 31 male adult 62 sides – 6.7 ± 1.9 – Distance from IOF to –
et al. Caucasian skulls inferior orbital fissure:
(2002) 31.9 ± 3.9
Cutright 80 adult 40 heads – Males: 16.9 ± 0.3 Males: – All measurements
et al. cadaveric heads of blacks Females: 25.7 ± 0.2 1
29.5 ± 0.5 were taken from
(2003) Females: center of IOF;
2
26.4 ± 0.4 1,2
Significant
difference
40 heads – Males: 17.1 ± 0.3 Males: – 1,2
Significant
of whites Females: 25.8 ± 0.2 1
27.4 ± 0.5 difference
Females:
2
24.5 ± 0.3
Agthong 110 adult Asian 110 right – All: 7.8 ± 0.2 – Distance from IOF to 1,2
Significant
et al. skulls sides Males: 8.0 ± 0.2 anterior nasal spine: difference
(2005) Females: 7.5 ± 0.2 All: 34.1 ± 0.2
Males: 134.8 ± 0.3
Females: 232.8 ± 0.3
110 left All: 8.0 ± 0.2 Distance from IOF to 1,2
Significant
sides Males: 8.2 ± 0.2 anterior nasal spine: difference
Females: 7.8 ± 0.2 All: 34.3 ± 0.2
Males: 135.0 ± 0.3
Females: 233.1 ± 0.3
(continued)
82 6 Infraorbital Region
Table 6.3 (continued)
Distance
between
Distance between IOF and Distance between IOF
IOF and inferior facial and other anatomical
Author(s) Study material N Size of IOF orbital rim midline structures Comments
Robinson 20 cadaveric 40 sides – 6.8 (4.6–10.4) – – –
and heads
Wormald
(2005)
Song et al. 50 Korean 70 sides *5.0 ± 1.0 – – – *Longest diameter
(2007) cadaveric heads
Gupta 79 adult dry 178 sides 3.7 ± 0.9 7.0 ± 1.6 (3.2–13.2) 28.5 ± 2.6 All measurements
(2008) skulls (from a (1.8–6.9) (22.1–34.8) were taken from
Northwest Indian center of IOF
population)
Abed et al. 24 cadaveric 47 sides – 8.95 ± 1.53 – Distance from IOF to No side or sex
(2011) heads inferior orbital fissure: related significant
25.4 ± 2.7 differences
Chrcanovic 80 adult dry 160 sides All: All: 6.41 ± 1.69 All: Distance from IOF to 1,2
Significant
et al. skulls (108 3.23 ± 0.81 (3.2–12.1) 25.3 ± 2.6 anterior nasal spine: differences
(2011) females, (1.4–7) Males: 6.63 ± 1.75 (18.3–33.1) All: 32.4 ± 2.6 between males and
52 males) Males: (3.7–12.1) Males: (24.9–40.7) females
3.31 ± 0.81 Females: 6.35 ± 1.67 1
26.5 ± 2.6 Males: 133.8 ± 2.2
(1.5–5) (3.2–10.1) (21.5–33.1) (29.8–40.7)
Females: Females: Females: 231.7 ± 2.5
3.20 ± 0.81 2
24.7 ± 2.4 (24.9–37.1)
(1.4–7) (18.3–30.7) Distance from IOF to
nasal aperture: All:
14.7 ± 2.02 (10.5–20.1)
Males: 15.4 ± 1.79
(12.5–20.1)
Females: 14.4 ± 2.04
(10.4–19.4)
Singh 55 dry Indian 110 sides Vertical: 6.2 ± 1.8 (2–11) – Horizontal distance to –
(2011) skulls 3.6 ± 1.0 nasal aperture:
(1–6) 15.6 ± 2.6 (6.5–21)
Horizontal:
3.4 ± 1.3
(1.5–6)
Takahashi 28 Japanese 56 sides *All: 5.5 – – – *Transverse
et al. cadavers (4–7.5) diameter
(2011) Males: 15.7 (mediolateral)
(4–7.5) 1,2
Significant
Females: 25.1 difference
(4–7)
Lee et al. 240 Korean 480 sides – Right side: – – 1,2
Significant
(2012) patients (CT) 240 males All: 8.42 difference
(mean age 240 Males: 18.49 ± 1.5
30.9 years, range females Females:
6 months – 88 2
8.33 ± 1.5
years) Left side:
All: 8.42
Males: 18.50 ± 1.6
Females:
2
8.34 ± 1.8
Xu et al. 112 patients 224 sides – Right side: – – –
(2012) (spiral CT) (138 All: 9.3 ± 1.68
(mean age females, Males: 9.3 ± 1.55
30.7 years, range 86 males) Females: 9.2 ± 1.90
15–57 years) Left side:
All: 9.0 ± 1.52
Males: 9.2 ± 1.33
Females: 8.8 ± 1.76
Infraorbital Foramen 83
Table 6.3 (continued)
Distance
between
Distance between IOF and Distance between IOF
IOF and inferior facial and other anatomical
Author(s) Study material N Size of IOF orbital rim midline structures Comments
Hwang 100 patients 200 sides – All: 9.6 ± 1.7 All: Distance from IOF to 1,2
Significant
et al. (high-resolution (74 males, (5.6–15.2) 26.5 ± 1.9 anterior nasal spine: difference
(2013) CT) (mean age 126 Males: 9.4 ± 1.6 (21.9–31.5) 35.0 ± 2.6 (28.5–43.9)
47.5 ± 17.9 years, females) Females: 9.7 ± 1.7 1
Males: 1
Males: 36.9 ± 2.2
range 19–75 26.9 ± 1.9 2
Females: 34.0 ± 2.3
years) 2
Females:
26.1 ± 1.8
Michalek 5 adult human 10 sides – Ultrasound: 17.6 ± 1.3 – – 1,2
Significant
et al. skulls Direct measurement: difference
(2013) 2
6.7 ± 0.9
Aggarwal 67 dry Indian 133 sides Vertical: 6.33 ± 1.39 25.7 ± 2.37 Horizontal distance –
et al. skulls 3.54 ± 1.11 (3.1–12.9) (19.3–32.0) from IOF to nasal
(2015) (1.3–7.0) aperture: 15.2 ± 1.70
Horizontal: (10.0–19.6)
2.72 ± 0.95 Distance from IOF to
(1.0–5.5) alveolar bone crest:
28.4 ± 2.82 (20.5–34.8)
84 6 Infraorbital Region
1 5.7 – 9.7 mm
2
4 14.7 –
17.2 mm
31.7 –
36.9 mm
5 35 mm 3
24.5 – 29.5 mm
Fig. 6.13 Reported mean distances from the infraorbital foramen (IOF) to adjacent anatomical structures. 1 = IOF to infraorbital margin, 2 = IOF
to nasal aperture, 3 = IOF to facial midline, 4 = IOF to anterior nasal spine, 5 = IOF to canine crestal bone
Multiple Foramina 85
AIOF
ZMS
IOC
IOF
Orbit
Orbit
ZMFF
AIOF
Zygomatic bone AIOF NAp
ZMS Zygomatic bone
IOF
IOF ZMS
ZMS
NAp
CP CP
Canine
ringe
Fig. 6.15 A 3D rendering from CBCT images of a right midface show- Fig. 6.17 A 3D rendering of CBCT scans of the left midface showing
ing an accessory infraorbital foramen in a 66-year-old female. AIOF an accessory infraorbital foramen in a 48-year-old male. AIOF acces-
accessory infraorbital foramen, CP coronoid process, IOF infraorbital sory infraorbital foramen, CP coronoid process, IOF infraorbital fora-
foramen, NAp nasal aperture, ZMS zygomaticomaxillary suture men, NAp nasal aperture, ZMFF zygomaticofacial foramen, ZMS
zygomaticomaxillary suture
orbit
AIOF
MS IOF
MS
CSin IOF
AIOF
LD
NAp
Maxillary sinus
Fig. 6.16 Coronal CBCT view of the infraorbital region showing the Fig. 6.18 Reformatted axial CBCT (inferomedial view) at the level of
infraorbital foramen, accessory infraorbital foramen, and associated the infraorbital foramen and the accessory infraorbital foramen. AIOF
structures. AIOF accessory infraorbital foramen, CSin canalis sinuosus, accessory infraorbital foramen, IOF infraorbital foramen, LD lacrimal
IOF infraorbital foramen, MS maxillary sinus, NAp nasal aperture duct
Multiple Foramina 87
AIOF
IOF
AIOC
LD IOC
IOC
Maxillary sinus
Maxillary sinus
IOC
IOG
Fig. 6.19 Reformatted axial CBCT (inferior view) showing the canal
leading to the accessory infraorbital foramen. AIOF accessory infraor- Fig. 6.20 Reformatted axial CBCT (inferolateral view) showing the
bital foramen, AIOC accessory infraorbital canal, IOC infraorbital infraorbital canal leading to the infraorbital foramen. IOC infraorbital
canal, LD lacrimal duct canal, IOF infraorbital foramen, IOG infraorbital groove
88 6 Infraorbital Region
Infraorbital Nerve and Artery labial branch that innervate the skin of the lateral side of the
upper lip and its mucosa. Various dividing patterns of the
The ION is the terminal branch of the maxillary nerve (second branches of the IOA were also observed. In most situations
division of CN V) (Figs. 6.21 and 6.22). It usually provides (73.8 %) the IOA was found in the middle of the ION bun-
three proximal alveolar branches, i.e., the posterior, middle, dle, but after exiting the IOF, the artery was located most
and superior alveolar branches, before emerging from the IOF often superficially to the nerve (73.8 %) (Fig. 6.23). The
(see below). The distal branches of the IOF supply the skin and authors further noted that within the space below the IOF,
mucous membranes of the middle portion of the face. Having branches of the ION coursing downward and branches of
traversed the floor of the orbit in the infraorbital groove and the facial nerve coursing forward form the infraorbital
canal, the ION enters the face at the IOF by passing between plexus. These two nerves were observed to either meet or
the levator labii superioris and levator anguli oris muscles cross over each other and were entangled hazardously (Hu
before reaching the skin (Robinson and Wormald 2005). et al. 2006). In a detailed microscopic dissection study of 16
In a dissection study of 43 embalmed hemifaces, five cadaveric heads, connections between cutaneous sensory
dividing distal branches of the ION were described (Hu branches of the ION and fine motor branches of the facial
et al. 2006): (1) the inferior palpebral branch, which inner- nerve were found in the infraorbital area. The mean number
vates the skin of the inferior eyelid and the conjunctiva; (2) of admixed nerves was 7.8 (±1.2). Ninety-six percent of the
the external nasal branch, which innervates the skin of the admixed nerves were found in a circle (diameter 36 mm)
lateral surface of the nose; (3) the internal nasal branch, with its center located 22 mm below the IOF (Hwang et al.
which innervates the nasal septum and nasal vestibule; (4) 2004a).
the medial sub-branches of the superior labial branch that In a microdissection study of ten cadaveric hemifaces,
innervate the skin on the center portion of the upper lip and each branch of the ION was traced under the microscope as
its mucosa; and (5) the lateral sub-branches of the superior far as its terminal reached the dermis (Hwang et al. 2004b).
ON
CN V ZN
TGG
MX
Fig. 6.21 Illustration of the right ION
maxillary nerve and its branches. IP EN
ASAN anterior superior alveolar MN
PPG
nerve, CN V fifth cranial nerve
IN
(trigeminal nerve), EN external
nasal branch of ION, GPN SL
greater palatine nerve, IN internal GPN
LPN
nasal branch of ION, ION MSAN ASAN
infraorbital nerve, IP inferior
palpebral branch of ION, LPN PSAN
lesser palatine nerve, MN
mandibular nerve, MSAN middle
superior alveolar nerve, MX
maxillary nerve, ON ophthalmic
nerve, PPG pterygopalatine
ganglion, PSAN posterior
superior alveolar nerve, SL
superior labial branch of ION,
TGG trigeminal ganglion, ZN
zygomatic nerve
Infraorbital Nerve and Artery 89
IOM
ION EN
IP
Fat tissue
of orbit
EN
IOA
IN
Fig. 6.23 Dissection of a right
midface in a male cadaveric SLl
head showing the infraorbital
artery and branches of the
infraorbital nerve. EN external
nasal branch of ION, IN SLm
internal nasal branch of ION,
IOA infraorbital artery, SLl
lateral portion of superior
labial branch of ION, SLm
medial portion of superior
labial branch of ION
90 6 Infraorbital Region
A mean of 19.5 cutaneous branches (range 15–24) were dis- A detailed study of the topographic distribution area and
tributed over the infraorbital area, bounded superiorly by the the branching pattern of the ION were performed in 43
margin of the lower eyelid, inferiorly by a horizontal line cadaveric hemifaces by Hu et al. (2007). The inferior palpe-
crossing the mouth corners, medially 0.5 cm to the midline, bral branch was generally bifurcated, giving off a medial and
and laterally 2 cm posterior to the temporal canthus of the a lateral branch (58.1 %). The internal nasal branch ran supe-
eyes. The mean cutaneous area supplied by the ION was rior to the depressor septi nasi muscle, along the ala of the
25.8 cm2 (range 24.0–28.2 cm2). The mean area of the supe- nose. It supplied the skin of the philtrum and gave off a ter-
rior labial branch was 13.1 cm2 (range 11.2–14.3 cm2) and minal branch that supplied the nasal septum and the v estibule
broader than either the 7.5 cm2 (range 6.6–8.8 cm2) of the of the nose. The external nasal branch was distributed
lower palpebral branch or the 7.6 cm2 (range 6.7–9.3 cm2) of diversely supplying areas between the root and the ala of the
the external nasal branch. It was further observed that the nose. The superior labial branch was the largest branch of the
area supplied by the external nasal branch overlaps with the ION and produced the most sub-branches. These sub-
areas innervated by the inferior palpebral and superior labial branches were divided into the medial and lateral branches
branches. depending upon the area that they supplied.
Canalis Sinuosus 91
Orbital cavity
IOC MS
MS
AMC
CSin
AMC
Fig. 6.26 Coronal CBCT image (head slightly rotated to the left side)
showing the right canalis sinuosus in a 48-year-old male. The canalis
Fig. 6.24 Schematic illustration of the left canalis sinuosus originating sinuosus gives off two fine branches to the anterior maxilla. AMC
from the infraorbital canal accessory maxillary canal from CSin, CSin canalis sinuosus, IOC infra-
orbital canal, MS bays of anterior portion of maxillary sinus
Orbital cavity
IOC MS
MS
MS CSin MS MS
NApb
IC
CSin IC
CaNF Nasal
cavity
CSin
AMC
CSin
AMC
Fig. 6.25 Coronal CBCT image (head slightly rotated to the left side)
showing the right canalis sinuosus in a 62-year-old female. The canalis
sinuosus curves around the lateral and lower border of the nasal aper-
ture giving off branches to the anterior maxilla and nasal floor
(Copyright von Arx et al. 2013). AMC accessory maxillary canal from
CSin, CaNF canaliculus to nasal floor from CSin, CSin canalis sinuo- Fig. 6.27 Coronal CBCT image showing a canalis sinuosus bilaterally
sus, IOC infraorbital canal, MS bays of anterior portion of maxillary in a 52-year-old male. AMC accessory maxillary canal from CSin, CSin
sinus, NApb border of nasal aperture canalis sinuosus, IC inferior concha, MS maxillary sinus
Canalis Sinuosus 93
AIOF
ZMS NPC
IOF
AMC AMC
Nasal floor
CSin
Anast Maxillary
Maxillary sinus
sinus
Fig. 6.28 Volume rendering of CBCT images (anterolateral view of Fig. 6.30 Axial CBCT image showing bilateral branches to the ante-
left midface) showing the canalis sinuosus in a 53-year-old male. AIOF rior maxilla (region palatal to canines) emerging from the canalis sinu-
accessory infraorbital foramen, Anast anastomosis between CSin and osus. AMC accessory maxillary canal from CSin (with corticated
posterior superior alveolar nerve/artery (not shown), CSin canalis sinu- borders), NPC nasopalatine canal
osus, IOF infraorbital foramen, ZMS zygomaticomaxillary suture
CSin
CSin
AMC
AMC
AMC
Fig. 6.29 Coronal CBCT image showing bilateral branches to the Fig. 6.31 Sagittal CBCT image showing broad accessory maxillary
anterior maxilla emerging from the canalis sinuosus in a 44-year-old canal palatal to a lateral incisor in a 71-year-old male. CSin canalis
male. CSin canalis sinuosus, AMC accessory maxillary canal from CSin sinuosus, AMC accessory maxillary canal from CSin
94 6 Infraorbital Region
Anterior Superior Alveolar Nerve and Artery A recent morphometric-anatomical study evaluated the
course of the ASAN in ten fresh hemifaces (von Arx and
The anterior superior alveolar nerve (ASAN) and artery Lozanoff 2015). The ASAN arose lateral (six cases) or
(ASAA) arise from the infraorbital nerve and artery, respec- inferior (four cases) from the infraorbital canal at a mean
tively, within the orbital canal-groove complex (Figs. 6.32, distance of 12.2 ± 5.8 mm posterior to the IOF. After cours-
6.33, 6.34, 6.35, and 6.36). The ASAN and ASAA supply ing anterolaterally, the ASAN turned medially and was
the anterior maxillary teeth (canine to canine), their peri- located on average 5.5 ± 3.1 mm below the IOF. When
odontal and alveolar bone structures, as well as the buccal approaching the nasal aperture, the loop of the ASAN was
and palatal gingiva and mucosa. on average 13.6 ± 3.1 mm above the nasal floor. All evalu-
Heasman (1984) evaluated in detail 19 hemisectioned ated ASANs consisted of a single trunk including two to
heads with regard to the course of the ASAN. The diameter four fascicles. Six cases showed a branching pattern of the
of the ASAN was found consistently to be between one-half ASAN within the anterior wall of the maxillary sinus with
and one-third that of the ION and was a broader structure branches joining the middle or posterior superior alveolar
than either the posterior or middle superior alveolar nerves. nerves.
The ASAN branched from the parent trunk, coursed laterally
to the orbital margin, and then passed anteroinferomedially
below the IOF to the piriform aperture. The vertical distance
between the IOF and the ASAN varied considerably ranging
between 2 and 9 mm. Inconsistency was also noted in the
point of origin of the ASAN from the ION. In six specimens
it split from the ION within 5 mm of the IOF, whereas four ION
branched from the ION at distances greater than 20 mm from
the IOF, two of which were within 2 mm of entering the
IOC. In two dissections, a dual origin of the ASAN was seen.
OF
Murakami et al. (1994) assessed the superior alveolar IOA
nerves in 37 cadaveric heads following whole-mount silver
impregnation. They described that the ASAN, two to three in
number, arose from the ION after (!) its exit from the
IOF. The ASAN, after reentering the anterior surface of the ASAN
maxilla, divided into numerous twigs and formed the anterior
part of the superior dental plexus. The ASAN did not supply ASAA
the mucous membrane of the maxillary sinus.
Robinson and Wormald (2005) dissected 20 cadaveric
heads to evaluate the course and branching pattern of the ION
ASAN. In all 40 maxillae, the ASAN was identified with five
discrete patterns to its course and branches. The most com- ASAN
mon pattern was a single ASAN trunk with no branches OF
(30 %), followed by a single trunk with multiple branches
(25 %) and a single trunk with a single branch (20 %). Less
frequent was a double ASAN trunk with multiple branches
(15 %) or with no branches (10 %). In 87.5 % the ASAN was IOR
encased in thin bone during its course on the anterior aspect IOF IOR
of the maxilla, whereas in 12.5 % the ASAN was positioned
within an osseous dehiscence.
Song et al. (2012) investigated the branching point of the
ASAN canal from the IOC. Twenty-eight human cadaveric
hemimaxillae were scanned using microcomputed tomogra-
phy with subsequent 3D reconstruction. The branching point Fig. 6.32 Superior view of the right orbital floor after removal of the
of the ASAN canal from the IOC occurred at about one-third eye in a dissection of a decalcified right cadaveric hemiface (Copyright
von Arx and Lozanoff 2015). ASAA anterior superior alveolar artery,
along the length of the IOC in the anterior direction. The
ASAN anterior superior alveolar nerve, IOA infraorbital artery, IOF
canal arose either laterally (57.5 %), inferiorly (37.5 %), or infraorbital foramen, ION infraorbital nerve, IOR infraorbital rim, OF
medially (5 %) from the IOC (Song et al. 2012). orbital floor
Anterior Superior Alveolar Nerve and Artery 95
Arterial anastomosis
IOC
ION
IOF
SchM
ASAN
ASAN
MSpw
MSAN MSaw
IOF
SchM
ASAN
Fig. 6.36 Anterior view of the
MSAN
right midface of a decalcified
cadaveric head. All soft tissues
overlying the right maxillary
sinus have been removed 1
including the thin bone of the SchM 2
3 NAp
anterior wall of the maxillary
sinus (following decalcification)
(Copyright von Arx and Lozanoff
2015). ASAN anterior superior
alveolar nerve (with three
branches), IOF infraorbital
foramen, MSAN middle superior
alveolar nerve, NAp nasal
aperture, SchM Schneiderian
membrane
Clinical Relevance of the Infraorbital Region 97
According to Fitzgerald (1956) (cited in Heasman 1984), the Several methods have been proposed to clinically locate the
criteria of definition for a middle superior alveolar nerve IOF. Usually, a small depression is palpable at the inferior
(MSAN) are as follows: (1) that it is intermediate in position margin of the orbit. This depression called the infraorbital
between the ASAN and the posterior superior alveolar nerve notch is created by the zygomaticomaxillary suture. The IOF
(PSAN), (2) that it joins the premolar alveolar plexus, and lies approximately 6–10 mm inferior to the infraorbital rim in
(3) that it is not a branch of the ASAN. In the dissection that location, according to the data reported in Table 6.3.
study by Heasman (1984), seven specimens (36.8 %) satis- Interestingly, the location of the IOF corresponds to the loca-
fied these criteria. Five MSAN left the ION in the posterior tion of an acupuncture point in Chinese medicine, called Sibai
third and two MSAN left it in the middle third relative to the point. Its main indications are ocular problems, facial paraly-
IOC. Those with the posterior origin coursed anteroinferi- sis, headache, and vertigo. By pressing the point with a finger,
orly behind the root of the zygoma before branching and the function of the eyes is reported to improve (Xu et al. 2012).
contributing terminal fibers to the nerve plexus in the premo- The dissection studies mentioned above corroborate what
lar area. Those with the middle origin ran anterior and medial is seen clinically when the ION has been traumatized: a zone
to the root of zygoma ramifying as terminal branches in the of dysesthesia results that extends from the lower eyelid to the
nerve plexus. corner of the mouth as well as to the lateral nose (Eppley
In a study evaluating 37 cadaveric heads, the MSAN was 2004). The overlapping innervation areas of some of the ION
identified in 25 specimens (67.6 %) (Murakami et al. 1994). branches may account for sustaining sensory perception to
In 21 of the 25 cases, the nerve was seen from the inner some extent following damage to the ION (Hwang et al.
aspect of the maxillary sinus during its course through a can- 2004b) (Fig. 6.37). Much of the nerve’s overlap is found to be
aliculus. The nerve gave off two to three branches to the more medial along the nasolabial fold and nose. This probably
mucous membrane of the sinus. Under the mucous mem- explains the more prolonged and often permanent anesthesia
brane, that lined the upper wall of the sinus, the branches over the lateral cheek areas in some patients with zygomatic
formed a small network of fine twigs. However, the branches fracture that undergo long-term evaluation (Eppley 2004).
did not communicate closely with the nerve plexus of the However, direct trauma to the ION is rare, with the most com-
maxillary sinus. mon injury being indirect trauma resulting from compression
Robinson and Wormald (2005) dissected 20 cadaveric in connection with malar fractures. The nerve is well protected
heads to evaluate the course and branching pattern of the in its entire length from direct injuries. However, in cases in
MSAN. The MSAN was identified in nine maxillae (23 %). which the fracture travels through the canal, permanent pares-
It always presented as a single trunk either without branches thesia can occur (Kazkayasi et al. 2001).
or with multiple branches as opposed to the ASAN that dis- Regarding the interconnections between the ION and the
played a double trunk in some cases (as mentioned above). facial nerve in the immediate infraorbital area, a hazardous
All MSANs were encased in bone. zone of infraorbital plexus should be kept in mind when per-
Corbett et al. (2010) compared the ION block with a forming any procedures related to maxilla, zygoma, or deep
block of the ASAN/MSAN in which the local anesthetic was cheek injuries (Hwang et al. 2004a).
deposited in the palatal mucosa at a point that bisected the Two case reports have been published regarding iatro-
maxillary first and second premolars, midway between the genic globe penetration caused by a block of the ION (Saeedi
crest of the gingival margin and the midpalatine suture. The et al. 2011). In one case, a 33-year-old male patient was
study was performed in 20 healthy adult volunteers. The scheduled for rhinoplasty revision. An extraoral infraorbital
ION block produced anesthetic success in canine and premo- block was chosen with the needle inserted inferior to the ala
lar teeth, with a more rapid onset than that for the ASAN/ nasi and directed superolaterally toward the IOF. Ten min-
MSAN block. Although the latter was significantly more utes later, the right pupil was noted to be fixed and dilated
successful than ION block in attaining incisor anesthesia, it with conjunctival chemosis. Ophthalmoscopy revealed a
was ineffective for central incisors, as assessed according to retinal tear in the inferior periphery with associated vitreous
rigorous electronic pulp testing. hemorrhage resulting in passage of the needle through the
98 6 Infraorbital Region
IOC to the eye. In the second case, a 24-year-old male patient Another iatrogenic and inadvertent problem affecting the
presented with a left upper lid laceration (Chan et al. 2011). infraorbital space and the ION has been reported by Ikawa
Following administration of an ION block, the patient et al. (2012). Two patients required surgical removal of
became distraught with pain in his left eye and rapidly lost calcium hydroxide paste that was overfilled during root canal
the vision. An ophthalmologic examination revealed ele- treatment of an upper canine and a maxillary first premolar.
vated intraocular pressure and partial mydriasis. In addition, The paste leaked into the infraorbital space causing pain,
a c onjunctival entry wound and a vitreous bubble with nearby swelling, and hypesthesia. Since the bone may be absent
focal retinal blanching was present in his left eye. over the root apices of maxillary canines and buccal roots of
Regarding the least likelihood of disruption of the major first premolars due to fenestration defects, caution must be
nerve trunks of the ION and ASAN when performing canine exercised to avoid over-instrumentation and enlargement of
fossa punctures or antrostomies, Robinson and Wormald the apical foramen to avoid leakage or overfilling of root
(2005) recommended the safest entry point as the intersec- canal medicaments, pastes, and filling materials (Figs. 6.38,
tion of a vertical mid-pupillary line with a line through the 6.39, and 6.40).
floor of the piriform aperture. In all maxillae, the canine The ION block is an accepted local anesthetic injection
fossa puncture was made at this point with a 4 mm trocar. In technique. The use of an extraoral approach is routinely
five of the 40 maxillae, there was a disruption of a fine branch described in the medical literature. In contrast, the dental
from the ASAN. There was no disruption to the main trunk profession has advocated an intraoral approach (Kleier et al.
or any of the major branches of the ASAN and the MSAN. 1983) (Figs. 6.41 and 6.42). While the dental patient does
IP EN
SL
Fig. 6.41 Block anesthesia of the left infraorbital nerve (intraoral Fig. 6.42 Block anesthesia of the left infraorbital nerve (extraoral
approach): needle penetrates the mucosa in a fold of the vestibule above approach): needle penetrates the skin about 10 mm below infraorbital
canine and it is directed 10–15 mm toward the lateral canthus of the eye rim and two-thirds above ala of nose (compare with Fig. 6.10)
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Nasopalatine Canal
7
The nasopalatine canal (NPC) is a bone channel connecting (Figs. 7.6 and 7.7). The latter is located immediately deep to
the nasal cavity and the palate, hence its name (Fig. 7.1). the incisive papilla.
Since the NPC is located palatal to the central incisors, it is Four small foramina are positioned at the base of the naso-
also referred to as the incisive canal. The NPC is not to be palatine canal (Fig. 7.8). The foramina of Scarpa are positioned
confused with the nasopalatine duct, an epithelialized struc- along an anteroposterior axis and transmit the nasopalatine
ture within the NPC (see below). The NPC forms in the pos- nerve and its numerous branches. The foramina of Stensen are
terior part of the primary palate during fetal weeks 9–13 and positioned in a mediolateral orientation and transmit the naso-
not at the junction of the primary palate with the horizontal palatine vasculature as well as remnants of Jacobson’s organ
plates of the secondary palate, as normally described and when present (Thompson 1914; Jacob et al. 2000). Regarding
illustrated (Radlanski et al. 2004). Usually, the NPC origi- the incisive foramen, it was found to be doubled in 2 % of 100
nates bilaterally from the funnel-shaped openings (nasal skulls examined (Berge and Bergman 2001) (Figs. 7.9 and 7.10).
infundibula) that are located in the anterior part of the floor In a recent case report, a rare anatomical variation related
of the nasal cavity lateral to the nasal septum (Figs. 7.2, 7.3, to the nasopalatine canal was described (Neves et al. 2013).
7.4, and 7.5). In the sagittal plane, the NPC descends in a CBCT images of a 53-year-old female showed a complete
slightly oblique direction. In the (tilted) coronal plane, the additional NPC located anterior and superior to the primary
bilateral canals fuse approximately at the middle of their NPC. Each canal extended from independent nasal openings
total length to continue as a single canal. The NPC termi- to independent openings located in the remaining alveolar
nates with a palatal opening, the so-called incisive foramen process of the anterior maxilla.
ION/A
NCIw SCmc
SC
NPCrno
NPClno
ANS SC
HP
ANS
NPC
IF
CI
NPCrno
CaNF
ANS
106 7 Nasopalatine Canal
NPCIno
NPCrno
IM
IC
IM
NS
MS
MS
IC
ANS
NPCrno
Right Left
maxillary NPClno maxillary
sinus sinus
Nasal
floor
Fig. 7.5 Axial CBCT image (inferior view) exhibiting both nasal openings of
the nasopalatine canals in a 52-year-old male. ANS anterior nasal spine,
NPClno left nasal opening of the nasopalatine canal, NPCrno right nasal PNS
opening of the nasopalatine canal, PNS posterior nasal spine
7 Nasopalatine Canal 107
IF
MPS
NPCrno
MPS
108 7 Nasopalatine Canal
Fig. 7.8 Axial CBCT section below the nasal floor showing four dis-
tinct canals of the NPC constituting canals of Stensen (mediolaterally)
and Scarpa (anteroposteriorly) in a 46-year-old male Fig. 7.10 The axial CBCT scan shows this rare anatomical variation
with the duplicated canals positioned along the anteroposterior axis
(note: the right lateral incisor is missing)
The conventional intraoral radiographic images of the NPC The NPC shows great variability in its morphology (Fig. 7.12).
and of the nasopalatine foramen are usually projected between In the sagittal plane, four typical shapes of the NPC have been
the roots of the central incisors (Fig. 7.11). The “radio- described in the literature (Table 7.1). Most of the CT- and/or
graphic” foramen varies markedly in shape, size, and sharp- CBCT-based studies reported that the cylindrical shape of the
ness due to projection geometry and variability in anatomic NPC is the most frequently encountered shape. Mardinger
morphology. The lateral walls of the NPC may occasionally et al. (2008) found that in severely resorbed ridges, the fun-
be seen as a pair of radiopaque lines extending from the inci- nel-like shape prevailed (56.6 %). In a study of 163 dry human
sive foramen to the level of the nasal floor (Jacobs et al. 2007). skulls, a cone-shaped canal was predominantly found in small
The precision of radiography regarding the NPC was evalu- NPC (diameter < 3 mm) (Liang et al. 2009).
ated by Cavalcanti et al. (1999). They compared CT and physi- In the frontal view (inclined coronal view), the NPC may
cal measurements of the length of the NPC and the width of the radiographically appear as a broad single canal, as two narrow
alveolar bone labial to the incisive foramen in eight cadaveric canals, or as a Y-shaped canal with two to four branches in the
heads. There was no significant difference between the two upper portion (Fig. 7.13) (Table 7.2). A significant effect of the
techniques of measurements for the distance from the alveolar morphology of the NPC on the mean diameter of the incisive
crest to the anteroinferior point of the NPC (0.59 ± 1.19 mm) foramen was reported by Bornstein et al. (2011), with single
and for the length of the NPC (1.09 ± 2.15 mm). The authors canals presenting the largest mean diameter (4.45 mm).
concluded that 2D reformatted images from spiral CT permit- Song et al. (2009) used micro-CT to scan 57 anterior
ted highly accurate measurements of the NPC and thus pro- maxillae derived from dissected cadavers. Images were
vided a satisfactory quantitative presurgical examination for subsequently reconstructed using 3D software to determine
dental implantation (Cavalcanti et al. 1999). the morphology of the NPC. It was found that the lower por-
In a study of 18 human cadaveric jaws, high-resolution tion always was a single canal dividing into two to four
MRI images successfully showed the NPC with its neurovas- canals below the nasal floor. The dividing point was located
cular bundles (Jacobs et al. 2007). The images also showed at about the level of the upper fifth of the NPC. Most com-
branches of the NPC sprouting to the right and left of the canal monly, a single-channel NPC (42.9 %) was observed. In
posing a certain risk when placing implants in those areas. 23.2 % two channels were present, in 25 % three channels,
and in 8.9 % four channels. However, the superior openings
always consisted of one single bilateral nasal foramen, mean-
ing that three- and four-channel NPC configurations recom-
bined just below the nasal floor. In most cases with
multiple-channel patterns, the channels were separated com-
pletely from each other by a bony septum, but in some cases
the separation was incomplete. The authors further classified
the course of the NPC in the sagittal plane related to the nasal
floor as the horizontal reference (Song et al. 2009). The
course of the NPC was vertical straight in 46.4 % of the spec-
imens examined, with remaining patterns characterized as
vertical curved (14.3 %), slanted straight (32.1 %), and
slanted curved (7.2 %).
a b
c d
Fig. 7.12 CBCT images showing different shapes of the nasopalatine canal in the sagittal plane: (a) cylindrical shape, (b) funnel-like shape, (c)
hourglass-like shape, (d) “banana” shape
Morphology of the Nasopalatine Canal 111
Table 7.1 Shape of the nasopalatine canal (NPC) in the sagittal plane
Hourglass-like Banana-like Cone
Author(s) Study material N Cylindrical % Funnel-like % % % % Comments
Mardinger 207 patients (CT) 207 50.7 30.9 14.5 3.9 – –
et al. (2008) (mean age
58.1 years, range
16–86 years)
Liang et al. 163 dry skulls 162 53.7 – – – 46.3 One NPC could
(2009) not be classified
Tözüm et al. 933 patients (spiral 933 40.7 27.7 18.8 12.9 – Multicenter
(2012) or cone beam CT) study (four
(mean age centers)
43.8 ± 16.2 years,
range 18–84 years)
Güncü et al. 933 patients (CT 417 males Dentate: 34.6 Dentate: 28.2 Dentate: 21.2 Dentate: 10.5 – Same study
(2013) or CBCT) (mean Edentate: 35.2 Edentate: 31.4 Edentate: 22.9 Edentate: 16.0 material as in
age Tözüm et al.
43.8 ± 16.2 years, (2012)
range 18–84 years) 516 Dentate: 47.0 Dentate: 24.5 Dentate: 17.2 Dentate: 11.4 – –
females Edentate: 39.8 Edentate: 35.9 Edentate: 12.6 Edentate: 11.7
Etoz and 500 patients 490 8.6 27.4 38.8 14.7 9.2 Tree-branch
Sisman (2014) (CBCT) (mean age shape in 1.4 %
46.1 years, range
17–77 years)
Fernandez- 224 patients 224 48.7 20.5 30.8 – – –
Alonso et al. (CBCT) (mean age
(2015) 47.3 years)
112 7 Nasopalatine Canal
a b
c d
Fig. 7.13 CBCT images showing different morphologies of the nasopalatine canal in the frontal plane: (a) single and broad canal, (b) two parallel
canals, (c) Y-shaped canals, (d) multiple canals
Morphology of the Nasopalatine Canal 113
Angulation of the Nasopalatine Canal the control group (class A) was 1.8 mm for the palatal part and
0.7 mm for the nasal part of the NPC. In the severely resorbed
In a CT study assessing 120 patients, the NPC was inclined ridges (classes C–E), when the palatal canal opening was situ-
on average 77.4° (±8.9°) to the horizontal bone plate of the ated on the ridge, it occupied a mean area of 35.6 % of the
nasal floor (Liang et al. 2009). The slope between the NPC remaining ridge (range 13–58 %) available for implant place-
and the central incisors was on average 7.9° (±5.7°). In a ment in the region of the central incisors. Further, the buccal
CBCT study including 500 patients, the mean angle of the plate anterior to the NPC lost approximately 60 % of its mean
NPC relative to the nasal floor in the sagittal plane was width and decreased from 6.4 mm (class A) to 2.6 mm (class
73.3 ± 8.11° (Fernandez et al. 2014). Males (73.9°) presented E). The authors concluded that the static model of NPC shape
a wider angle than females (72.9°) but without a statistically be replaced by an active model with the NPC enlarging with
significant difference. age and mainly after tooth extraction or tooth loss.
Liang et al. (2009) evaluated 120 patients with spiral CT
and demonstrated significant gender differences with males
Width and Length of the Nasopalatine Canal having significantly longer and wider NPC than females.
Also the NPC was significantly longer in dentate (10.6 mm)
Several studies have assessed the length and the width (diam- compared to edentulous (9.2 mm) subjects, but no difference
eter) of the NPC (Fig. 7.14) (Table 7.3). Considering the dif- was found regarding the width (3.5 mm versus 3.6 mm). In
ferent methodology, the mean length of the NPC reported in contrast, linear regression showed a positive correlation
the literature ranged from 8.1 to 15.1 mm. The mean width between age and diameter of NPC.
of the NPC measured at the nasal opening ranged from 2.4 to In a CBCT study of 100 patients, the mean length of the
4.9 mm and at the palatal opening (incisive foramen) from NPC in males was significantly longer than in females
2.4 to 5.5 mm. The measurements for the diameter of the (Bornstein et al. 2011). In individuals with increasing age,
canal itself averaged between 2.0 and 4.3 mm (Table 7.3). the mean length significantly decreased. In a large multi-
Mardinger et al. (2008) assessed the length and diameter of center study with 725 subjects evaluated with CT, the length
the NPC in 207 CT images of patients before implant place- (12.0 mm versus 10.4 mm) and width (2.8 versus 2.4 mm) of
ment in the anterior maxilla and correlated the measurements the NPC was found to be significantly greater in males than
with the residual bony ridge that was classified into five differ- in females (Güncü et al. 2013). Absence of teeth in the ante-
ent stages according to the degree of atrophy (from class rior maxilla decreased the NPC length, but the canal diame-
A = full dentition in the premaxillary area to class E with severe ter remained unchanged.
atrophy of the alveolar crest). The mean canal length decreased The volume of the NPC was quantified in 252 patients using
from 10.7 mm (class A) to 9 mm (class E). The canal diameter CBCT scans and a specialized 3D software (Acar and
increased with the degree of ridge resorption at all measured Kamburoglu 2015). The mean volume was significantly greater
sites. The mean diameter enlargement (classes B–E) relative to (p = 0.042) in males (72.96 mm2) than in females (55.17 mm2).
Table 7.3 Size (mm) and length (mm) of the nasopalatine canal (NPC)
Size of nasal Size of palatal
Author(s) Study material N opening Size of NPC opening Length of NPC Comments
Cheng et al. NA (radiographs) NA – – – 15.05 ± 2.20 –
(1997)
Kraut and 30 patients (CT) 30 – – – 9.0 ± 2.3 (3–14) Only patients
Boyden(1998) (mean age 42 included with both
years, range central incisors
21–78 years) present
1
Berge and 100 dry skulls 100 – – 2.76 × 22.39 – 1
Longest diameter
Bergman (min: 10.46 × 2
Shortest diameter
2
(2001) 0.46 max: 15.5
× 24)
Mraiwa et al. 34 patients (spiral 34 4.9 ± 1.2 – 4.6 ± 1.8 8.1 ± 3.4 –
(2004) CT) (mean age 55
years, range
26–68 years)
1 1 1 1
Mardinger 207 patients (CT) 113 dentate 4.0 ± 1.4 3.3 ± 0.97 3.7 ± 0.78 10.7 Mesiodistal
2 2 2
et al. (2008) (mean age 2.5 ± 1.0 2.1 ± 0.78 2.9 ± 0.68 diameter
2
58.1 years, range Buccolingual
16–86 years) diameter
94 edentulous 14.3 ± 0.84– 1
3.6 ± 0.74– 1
4.1 ± 0.73– 9.0 1
Mesiodistal
4.6 ± 1.43 4.3 ± 1.28 5.5 ± 1.08 diameter
2 2 2 2
2.5 ± 0.87– 2.1 ± 0.74– 3.4 ± 0.84– Buccolingual
3.3 ± 1.04 2.5 ± 0.97 4.6 ± 0.76 diameter (range of
means for different
atrophy classes)
Liang et al. 163 dry human 163 – – *3.4 ± 0.9 – *Determined as
(2009) skulls coronal size
120 patients 120 – 3.6 ± 1.0 – 9.9 ± 2.6 –
(spiral CT) (age
range 16–73
years)
Song et al. 57 cadaveric 57 – – – All: 11.5 –
(2009) anterior maxillae (4.9–16.3)
(micro-CT) Dentate: 12.0
(8.4–15.8)
Edentulous:
10.4 (4.9–16.3)
Bornstein et al. 100 patients 100 *3.49 ± 0.15 – 4.45 ± 0.15 11.99 ± 0.27 All measurements
(2011) (CBCT) (mean (0.96–8.75) (1.46–9.71) (5.89–17.77) on sagittal images
age *In case of
43.1 ± 19.9 years) multiple openings,
values were added
Tözüm et al. 933 patients 725 dentate, All: 2.76 ± 1.40 All: 2.07 ± 0.92 All: 2.93 ± 1.01 All: Multicenter study
(2012) (spiral or cone 208 Dentate: Dentate: Dentate: 10.86 ± 2.67 (4 centers)
beam CT) (mean edentulous 2.77 ± 1.40 2.08 ± 0.93 2.90 ± 1.00 Dentate:
age Edentulous: Edentulous: Edentulous: 11.07 ± 2.70
43.8 ± 16.2 years, 2.73 ± 1.37 2.04 ± 0.89 3.02 ± 1.05 Edentulous:
range 18–84 10.16 ± 2.48
years)
Güncü et al. 725 dentate 312 males, – Males: Males: Males: 11.96 Multicenter study
(2013) patients (CT) 413 females *2.79 ± 0.94 3.22 ± 1.05 ±2.73 (four centers), all
(males: mean age Females: Females: Females: 10.39 measurements on
41.4 ± 15.8 years; *2.43 ± 0.85 2.67 ± 0.89 ±2.47 axial images;
females: mean age *mean values for
40.1 ± 15.6 years) measurements
taken at three
different levels
(continued)
116 7 Nasopalatine Canal
Distances from the Nasopalatine Canal than when one (6.1 mm) or both incisors (7.1 mm) were
present. Further the time period since loss of the central
Regarding measurements taken from the NPC to adjacent incisor(s) also affected the bone width significantly, i.e., the
anatomical structures, the following dimensions were longer one or both incisors were missing, the thinner the
assessed: the labial and palatal bone widths relative to the bone labial to the NPC (Bornstein et al. 2011).
NPC, the horizontal distance between the NPC and the roots In a study comparing dentate (n = 725) and edentulous
of the central incisors, and the vertical distance from the inci- (n = 208) patients with either spiral or cone beam CT, bone
sive foramen to the bone crest (Table 7.4). Males exhibited a dimensions anterior to the canal differed significantly accord-
significantly thicker labial bone plate than females (Bornstein ing to the presence or absence of teeth (Tözüm et al. 2012).
et al. 2011). The presence or absence of the central incisors Mean length was longer (11.1 vs. 10.2 mm) and width of the
also significantly influenced the width of the labial bone bone anterior to the NPC was larger (7.4 vs. 6.4 mm) in den-
plate at the crestal level, i.e., if both incisors were missing, tate than in edentulous patients, and the differences were sta-
the mean bone thickness was significantly thinner (5.0 mm) tistically significant.
Table 7.4 Distances (mm) from the nasopalatine canal (NPC) to adjacent anatomical structures
Distance Distance
from between
incisive NPC and
Width of bone foramen to roots of
plate labial to marginal central
Author(s) Study material N NPC bone crest incisors Other Comments
Cheng et al. (1997) NA (radiographs) NA 7.80 ± 1.43 – 4.15 ± 1.48 – –
Mraiwa et al. 34 patients (spiral 34 *7.4 ± 2.6 – – – *Mean value for
(2004) CT) (mean age 55 (2.9–13.6) measurements
years, range 26–68 taken at three
years) different levels
Mardinger et al. 207 patients (CT) 113 dentate 6.4 – – – –
(2008) (mean age 58.1 years,15 edentulous 2.6 – – – –
range 16–86 years) patients with
severe bone
atrophy
Liang et al. (2009) 163 dry human skulls 163 – 9.4 ± 2.1 – – –
Bornstein et al. 100 patients (CBCT) 100 At crest: – – – All
(2011) (mean age 6.49 ± 0.17 measurements in
43.1 ± 19.9 years) (2.38–11.0) sagittal
At midway of dimension
NPC: 7.59 ± 0.17
(3.57–12.63)
Taschieri et al. 57 patients (CT) (age 59 central – – *4.71 ± 1.26 – *Measured at
(2012) NA) incisors 4 mm from apex
Tözüm et al. 933 patients (spiral or 725 dentate, All: 7.17 ± 1.49 – – Width of *Mean values for
(2012) cone beam CT) (mean 208 edentulous Dentate: bone palatal measurements
age 43.8 ± 16.2 years, 7.38 ± 1.42 to NPC: taken at three
range 18–84 years) Edentulous: All: different levels
6.43 ± 1.49 4.78 ± 1.29
Dentate:
4.88 ± 1.29
Edentulous:
4.44 ± 1.23
Güncü et al. (2013) 725 dentate patients 312 males, 413 Males: – – – *Mean values for
(CT) (males: mean females *7.80 ± 1.37 measurements
age 41.4 ± 15.8 years; Females: taken at three
females: mean age *7.06 ± 1.37 different levels
40.1 ± 15.6 years)
Fernandez et al. 224 patients (CBCT) 108 males All: 6.1 ± 1.28 – – – Measured at one
(2014) (mean age 116 females (3.2–9.9) third of crest
47.3 ± 15.4 years, Males: 17.3 ± 1.28 height
1,2
range 18–84 years) Females: Significant
2
6.4 ± 1.14 difference
Acar and 252 patients (CBCT) 115 males Males: 16.6 – – – 1,2
Significant
Kamburoglu (mean age 48 years, 137 females Females: 26.0 difference
(2015) range 19–78 years)
NA not available
118 7 Nasopalatine Canal
Content of the Nasopalatine Canal within the pterygopalatine fossa, the sphenopalatine nerve
enters the nasal cavity via the sphenopalatine foramen. It then
The neurovascular bundle within the NPC contains the naso- passes medially across the root of the nose, below the natural
palatine arteries, veins, and nerves (Fig. 7.15). Song et al. ostium of the sphenoid sinus, to the upper border of the poste-
(2009) evaluated histologically the content of the NPC in 57 rior nasal septum. The nerve then runs obliquely downward
cadaveric anterior maxillae. The number of arteries corre- and forward on the septum between the mucous membrane and
lated with the number of bone channels whereas numerous the periosteum/perichondrium, until it reaches the nasal open-
veins were observed regardless of the number of bone chan- ing of the NPC at the anterior midline of the nasal floor. The
nels. Blood vessels were located in both the central and lat- nasopalatine nerve traverses the NPC and the incisive foramen
eral channels of the NPC. In contrast, the nerves were found to supply the palatal gingiva and mucosa of the premaxilla and
mainly in the central channel or in the most central of the joins with the distribution of the greater palatine nerve, thus
lateral channels. The number of nerve bundles did not cor- providing dual innervation to the primary palate. In addition to
relate with the number of channels and was generally >2. providing sensation to the septum and anterior palate, the naso-
Four human maxillary jaw specimens were histologically palatine nerve also carries sympathetic and parasympathetic
assessed by Liang et al. (2009). The NPC contained a large fibers that control secretions in the septal and palatal mucosa
artery surrounded by veins and myelinated nerves, with the (Chandra et al. 2008).
myelinated nerve bundle most probably being the nasopala- The nasopalatine artery, a branch from the sphenopalatine
tine nerve. Seromucous glands were also observed within artery that originates from the maxillary artery within the
the NPC. pterygopalatine fossa, runs with the nasopalatine nerve and
The nasopalatine nerve, previously known as the long sphe- courses downward and obliquely along the nasal septum to
nopalatine nerve, originates from the sphenopalatine nerve that reach the NPC (Fig. 7.16). The nasopalatine artery traverses
is a branch from the maxillary division of the trigeminal nerve the NPC to anastomose with terminal branches of the greater
(CN V). After passing through the pterygopalatine ganglion palatine artery in the anterior palate (Fig. 7.17).
ANS
NPA
GPA
Fig. 7.17 Nasopalatine artery emerging from the incisive foramen and
showing communications with branches of the greater palatine artery in
a dissected cadaveric head. GPA greater palatine artery, NPA nasopala-
tine artery
120 7 Nasopalatine Canal
a b
NPN
NPD NPD
NPA NPA
Fig. 7.18 Illustration of the contents of the nasopalatine canal: (a) overview of hard palate; (b) content of the nasopalatine canal. NPA nasopala-
tine artery, NPD nasopalatine duct, NPN nasopalatine nerve
Fig. 7.23 In this axial CBCT image, the gutta-percha point is visible in
Fig. 7.21 A sagittal CBCT image through the left nasopalatine canal the left area of the nasopalatine canal (arrow). The accessory maxillary
shows the gutta-percha point reaching the left nasal cavity bone canal (arrowhead) is positioned palatal to left lateral incisor
Fig. 7.22 A sagittal CBCT section at the level of the left lateral incisor Fig. 7.24 A axial CBCT section slightly above the nasal floor shows
depicts a broad maxillary bone canal (arrows) palatal to the tooth (see the tip of the gutta-percha point (arrow) entering the left nasal cavity
Chap. 6) through the infundibulum
Nasopalatine Duct 123
Fig. 7.25 Bilateral openings (arrows) of patent nasopalatine ducts in a Fig. 7.26 Two gutta-percha points (arrows) are inserted into the patent
24-year-old male. The inconspicuous openings are located lateral to the nasopalatine ducts
incisive papilla (arrowhead)
Fig. 7.27 The sagittal CBCT image shows the gutta-percha point in Fig. 7.28 Both gutta-percha points are visible in the coronal CBCT
the right nasopalatine duct view
124 7 Nasopalatine Canal
Fig. 7.29 In this axial CBCT image, both gutta-percha points are evi- Fig. 7.31 Posterior view of a 3D rendering of CBCT images: tip of
dent (arrows); furthermore, a maxillary bone canal (arrowhead) is seen gutta-percha point (arrow) reaching the right nasal cavity through large
palatal to the interradicular space of the left lateral incisor and canine infundibulum. Both gutta-percha points (arrowheads) are introduced
through the patent palatal openings (arrowheads) of the nasopalatine
ducts
Clinical Relevance of the Nasopalatine Canal surgical procedures in the anterior palate that would require
elective division of the neurovascular bundle at the incisive
The anatomical variability in morphology and dimensions of foramen, no areas of anesthesia could be detected after a mean
the NPC together with the variability of the neurovascular con- follow-up of 11 days by objective tests, and none of the patients
tent call for awareness during clinical procedures in the maxil- reported any subjective alteration in palatal sensation (Langford
lary central incisor region. This may be of clinical importance 1989). The author concluded that nasopalatine nerve section
in administration of local anesthesia, palatal surgery, and did not affect the sensitivity of the hard palate and that the
implant surgery (Liang et al. 2009). Implant rehabilitation of greater palatine nerves must be capable of providing normal
the edentulous anterior maxilla remains a complex restorative sensation to the mucosa of the entire hard palate. Moreover, the
challenge. Intricate preexisting anatomy dictates meticulous bone channels from the canalis sinuosus may convey sensory
and accurate osteotomy planning. With progressive bone loss, branches to the anterior palate (Chap. 6) (von Arx et al. 2013).
the alveolar crest may approach anatomical structures with the A recent study retrospectively assessed 20 patients follow-
nasopalatine nerve and vessels emerging from the ridge crest ing posterior partial lateralization of the nasopalatine nerve at
(Figs. 7.32, 7.33, and 7.34) (Mardinger et al. 2008). Because of the incisive foramen in conjunction with ridge augmentation
the close anatomical relationship between the NPC and the in the anterior maxilla (Urban et al. 2015). Subjectively, none
roots of the central maxillary incisors, a careful radiological of the patients complained about altered sensation in the ante-
analysis is necessary when insertion of a dental implant is rior palate, while clinical examination after a mean period of
planned in that region (Bornstein et al. 2011). Bone resorption 4.2 years revealed mucosal sensitivity changes in six patients.
together with an enlarged incisive foramen challenges proper The authors calculated a risk for neurosensory change in the
implant placement (Artzi et al. 2000). Following extraction or anterior palate of 0.45 mucosal teeth regions per patient fol-
loss of central incisors, resorption of the labial bone plate lowing lateralization of the nasopalatine nerve.
reduces the bone volume adjacent to the NPC and increases the The presence of a patent NPD has been associated with
risk of implant insertion into the NPC. Several authors several clinical issues. It may entice to perform endodontic
addressed this problem and published case reports or case treatment of healthy maxillary anterior teeth because the
series regarding how to surgically manage the situation presence of a palatal “fistula” may simulate an endodontically
(Figs. 7.35, 7.36, 7.37, 7.38, 7.39, 7.40, 7.41, 7.42, 7.43, and related sinus tract (Moss et al. 2000). In a case report, a patent
7.44) (Table 7.5). Interestingly, permanent sensitivity changes NPD led to misdiagnosis and surgical closure of a nonexist-
in the anterior maxilla were not identified in those case reports. ing oroantral communication following removal of a maxil-
Liang et al. (2009) cautioned that contact of dental implants lary left third molar (Valstar and van den Akker 2008).
with nervous tissue of the NPC might cause non-osseointegra- The clinician cannot easily identify patent NPD without
tion of the implant. Chandra et al. (2008) reviewed 107 nasal reported symptoms. Pathology in the incisive papilla region is
septal surgeries regarding anterior palate sensory impairment. uncommon, so it is not usually scrutinized carefully during an
Overall three patients (2.8 %) experienced postoperative numb- intraoral examination increasing the chance of missing the pat-
ness of the anterior palate. Two of these patients underwent ent NPD (Lundner and Warunek 2006). Clinicians are reminded
septoplasty and the third patient underwent septal perforation even though a patent NPD is a rare entity, one cannot ignore the
repair. In all three patients, a chisel was used to resect a portion possibility. Therefore, the presence of a patent duct should be
of the maxillary crest posterior to the nasal spine. In two considered prior to treatment of the adjacent teeth.
patients, normal sensation was present after 3 months, but in The development of NPD cysts has also been related to
the third patient, in whom cautery had been used, numbness the persistence of partially or totally patent forms of the NPD
persisted at the 1-year follow-up. However, there is evidence and its epithelial cell remnants found in the interior of the
for significant overlap of the sensory distributions of the naso- NPC (Falci et al. 2013). Several case reports have described
palatine nerve and the greater palatine nerve in the anterior pal- the development of a nasopalatine duct cyst in conjunction
ate (Langford 1989; Filippi et al. 1999), accounting for the low with immediate or late implant placement after extraction of
number of patients experiencing palatal numbness after septal central incisors (Casado et al. 2008; Sivolella et al. 2013;
surgery (Chandra et al. 2008). In a clinical study of 59 patients Takeshita et al. 2013). The authors speculated that implant
(mean age 23 years, range 9–48 years) with removal of bed preparation had perforated the nasopalatine canal and
impacted and palatally displaced maxillary canines, sensitivity the trauma had stimulated the proliferation of the embryo-
alteration was studied following intentional surgical section of logic epithelial remnants of the NPD.
the neurovascular bundle at the incisive foramen to ease eleva- Some reports have addressed the development of patent
tion of the palatal flap (Filippi et al. 1999). Though all patients NPD in conjunction with orthodontic palatal expansion
had objective sensitivity alterations after 1 week, at the 4-week (Eppley and Delfino 1988; Lundner and Warunek 2006;
follow-up neither subjective nor objective sensory deficits were Pithon 2011). The authors hypothesized that widening of the
diagnosed in any of the patients. In a similar study including 20 palatal suture following orthodontic maxillary expansion
patients (mean age 17 years, range 12–31 years) undergoing opened a preexisting NPD.
126 7 Nasopalatine Canal
Fig. 7.34 After removal of the soft tissue, the bone defect in the pre-
maxilla exhibits a typical heart-shaped configuration (arrow)
Fig. 7.33 Intraoperative view shows the large incisive foramen and the
dissected neurovascular bundle (arrow). No cystic lesion was present
Clinical Relevance of the Nasopalatine Canal 127
*
NPC
Fig. 7.38 Intraoperative view after preparation of the implant bed (*).
A thin bone wall (arrow) remains intact toward the nasopalatine canal.
Fig. 7.35 Axial CBCT image: for prosthetic reasons only, one implant
NPC nasopalatine canal (with neurovascular bundle)
was planned in the central incisor area with a distal cantilever. Note the
proximity of the nasopalatine canal to the implant site
* *
Fig. 7.42 The intraoperative view confirms the atypical location of the
widened nasopalatine canal (*). The neurovascular content of the canal
Fig. 7.40 The axial CBCT image shows the obvious “dislocation” of has been surgically removed
the nasopalatine canal (*) toward the alveolar ridge in a 20-year-old
male with avulsion of his right central incisor at the age of 8 years
*
* Fig. 7.43 Augmentation of the area with a mixture of autogenous bone
chips and demineralized bovine bone mineral particles
Fig. 7.41 The sagittal CBCT image demonstrates that the nasopalatine
canal (*) occupies a large part of the alveolar process
the vomeronasal organ in humans and chimpanzees, with a com- of maxillary incisive canal characteristics related to dental implant
parison to other primates. Anat Rec. 2002;267:166–76. treatment with computerized tomography: a clinical multicenter
Song WC, Jo DI, Lee JY, Kim JN, Hur MS, Hu KS, Kim HJ, Shin C, Koh study. J Periodontol. 2012;83:337–43.
KS. Microanatomy of the incisive canal using three-dimensional Urban I, Jovanovic SA, Buser D, Bornstein MM. Partial lateraliza-
reconstruction of microCT images: an ex vivo study. Oral Surg Oral tion of the nasopalatine nerve at the incisive foramen for ridge
Med Oral Pathol Oral Radiol Endod. 2009;108:583–90. augmentation in the anterior maxilla prior to placement of dental
Spin-Neto R, Bedran TB, de Paula WN, de Freitas RM, de Oliveira implants: a retrospective case series evaluating self-reported data
Ramalho LT, Marcantonio E. Incisive canal deflation for correct and neurosensory testing. Int J Periodontics Restorative Dent.
implant placement; case report. Implant Dent. 2009;18:473–9. 2015;35:169–77.
Takeshita K, Funaki K, Jimo R, Takahashi T. Nasopalatine duct cyst devel- Valstar MH, van den Akker HP. Patent nasopalatine duct: a diagnostic
oped in association with dental implant treatment: a case report and pitfall. Br J Oral Maxillofac Surg. 2008;46:304–5.
histopathological observation. J Oral Maxillofac Pathol. 2013;17:319. von Arx T, Bornstein MM. The patent nasopalatine duct. A rare anom-
Taschieri S, Weinstein T, Rosano G, del Fabbro M. Morphological fea- aly and diagnostic pitfall (article in German). Schweiz Monatsschr
tures of the maxillary incisors roots and relationship with neigh- Zahnmed. 2009;119:379–89.
bouring anatomical structures: possible implications in endodontic von Arx T, Lozanoff S, Sendi P, Bornstein MM. Assessment of bone
surgery. Int J Oral Maxillofac Surg. 2012;41:616–23. channels other than the nasopalatine canal in the anterior maxilla
Thompson P. Section II. Osteology. In: Jackson CM, editor. Morris’s using limited cone beam computed tomography. Surg Radiol Anat.
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M, Al-Hezaimi K, Al-Sadhan R, Karabulut E, Wang HL. Evaluation 2014;27:856–60.
Posterior Maxilla
8
The posterior maxilla includes the region of the upper jaw implant placement in edentulous patients suffering from
from the first premolar to the pterygoid process (Fig. 8.1). severe alveolar bone atrophy of the maxilla.
The posterior maxilla is formed by a fusion of several bones: Though upper third molars are much less frequently
the maxillary bone, the palatine bone, the zygomatic bone, removed than lower third molars, the posterior maxilla is
and the pterygoid plates of the sphenoid bone (Cheung et al. an important area for local anesthesia and surgical proce-
1998). From a lateral view, the alveolar process of the os dures including orthognathic surgery, removal of posterior
maxilla is clearly visible together with the zygomatic but- maxillary teeth/roots or cysts, surgical maintenance of
tress overlying the first molar roots (Fig. 8.2). The posterior posterior maxillary teeth (apical surgery, root resections,
or infratemporal surface of the os maxilla forms the anterior periodontal surgery), and placement of dental or orthodon-
wall of the infratemporal fossa (Figs. 8.3 and 8.4) (du Toit tic implants. The clinician must have a profound knowl-
and Nortjé 2003). While the maxillary sinus and the hard/ edge of the anatomy of the posterior maxilla to successfully
soft palate will be addressed in the following chapters, the perform anesthetic and surgical interventions and to avoid
present chapter focuses on the posterior alveolar process of problems associated with the neurovascular anatomy in
the os maxilla and its neighboring structures, such as the that region. For example, the posterior maxilla is the most
zygomatic bone and the pterygoid process. The latter two common site of hemorrhage in maxillary osteotomies
have recently gained much interest in conjunction with (Cheung et al. 1998).
PTP ZMA
OMa
OMa
ZB PPF
PSAAfor
ZMA
OM
PTP
Fig. 8.2 Left side of a dry skull
showing details of the posterior
maxilla. Dotted line
pterygomaxillary fissure, M1 first OMa
OMa MT
molar, MT maxillary tuberosity,
OM os maxilla, OMa alveolar
process of os maxilla, PPF
pterygopalatine fossa, PSAAfor
foramina for entrance of posterior
superior alveolar arteries (PSAA),
PTP pterygoid process of M1
sphenoid bone, ZB zygomatic
bone, ZMA zygomaticomaxillary
arch (zygomatic buttress)
The Posterior Alveolar Process: Horizontal Dimensions 135
eye
IFS
PPF
* ZB
TBz
MSpw
PTP
ZMA
PTP
MT
M1
The Posterior Alveolar Process: Horizontal and 7.9 ± 2.26 mm at the molars while the same distance
Dimensions parameters recorded 3 mm below the crest were 5.2 ± 1.96 mm
at the premolars and 8.3 ± 2.57 mm at the molars. The width
The horizontal dimension of the posterior alveolar process is of the edentulous sites was reduced by 22.5–34.2 % com-
usually much larger compared to the anterior alveolar pro- pared to the width of the dentate sites. The average thickness
cess, mainly due to the wide orofacial diameter of the three- of the buccal bone plate of the premolars was 1.6 ± 0.48 mm
rooted molars. However, marked bone resorption and bone and of the molars 2.2 ± 0.84 mm at dentate sites, while the
remodeling are observed following tooth loss or removal of same parameters showed values of 1.4 ± 0.61 mm for the pre-
teeth in the posterior maxilla. Mean measurements of crestal molars and 1.7 ± 0.51 mm for the molars in the edentulous
bone width are summarized in Table 8.1 and in Fig. 8.5. specimens. The corresponding values for the lingual cortex
Katranji et al. (2007) quantitatively assessed the width of the thickness at dentate sites were 2.0 ± 0.33 mm at the premo-
posterior alveolar process in 28 cadaveric heads. In dentate lars and 2.4 ± 0.24 mm at the molars, while measures at eden-
sites, the width of the alveolar crest was clearly more narrow tulous sites were 1.6 ± 0.64 mm at the premolars and
at the premolars (6.7 ± 2.08 mm) compared to the molars 2.1 ± 0.66 mm at the molars.
(10.2 ± 1.30 mm) while these same parameters recorded Ono et al. (2008) assessed the cortical bone thickness
3 mm below the crest measured 7.9 ± 2.18 mm and using CBCT in 43 patients (mean age 24.0 ± 8.2 years) who
11.4 ± 2.49 mm, respectively. In edentulous sites, the width had undergone orthodontic mini-implant placement. The
of the alveolar crest in the premolar and molar regions were thickness of the cortex was measured mesial and distal to the
significantly less measuring 5.1 ± 2.20 mm at the premolars first molar from 1 to 15 mm below the crest at 1-mm intervals.
136 8 Posterior Maxilla
At the mesial location, the mean cortical thickness ranged width of the buccal mucosa at premolar and first molar sites
between 1.09 and 1.62 mm and at the distal location between ranged from 1.6 to 2.0 mm, whereas the palatal mucosa was
1.14 and 2.12 mm. Comparing mesial and distal locations, considerably larger ranging from 4.5 to 4.7 mm.
the latter demonstrated significantly thicker cortical bone at De Souza et al. (2013) assessed the bone width of 252
several heights. Also, the cortical bone in males was signifi- edentulous sites in the posterior maxilla of 122 patients
cantly thicker than in females at several heights. (mean age 57.5 years, range 21–92 years) using
Katsoulis et al. (2012) evaluated the relative bone width CBCT. Horizontal measurements were taken 2 mm below
in 52 edentulous patients (mean age 62 ± 9 years) using CT the margin of the alveolar crest. The mean width measured at
and an implant-planning software. The width of the com- first and second premolar and first and second molar sites
plete ridge in first premolar, second premolar, and molar was 6.3 mm, 7.4 mm, 9.2 mm, and 9.5 mm, respectively.
sites was 12.7 ± 2.0 mm, 13.3 ± 2.2 mm, and 15.4 ± 2.6 mm, Gender and age were not found to significantly influence the
respectively, and the thickness of the bone at those sites was width, but the morphology of the maxillary sinus floor had a
6.2 ± 1.6 mm, 6.9 ± 1.9 mm, and 9.0 ± 2.3 mm, respectively. significant effect. A flat configuration of the sinus floor was
The calculated width of the bone relative to the complete associated with an increase of mean bone width, whereas an
ridge was 48.8 % in first premolar sites, 51.9 % in second oblique configuration exhibited increased mean bone heights
premolar sites, and 58.4 % in first molar sites. The mean (de Souza et al. 2013).
Table 8.1 Summary of mean measurements reported for bone width (mm) of the posterior alveolar process
Dentate subjects Edentulous subjects
Premolar area 6.7–7.9 5.1–7.4
Molar area 10.2–11.4 7.9–9.5
a b
6.7–7.9 mm
5.1–7.4 mm
7.9– 9.5 mm
10.2–11.4 mm
The Posterior Alveolar Process: Vertical Farina et al. (2011) assessed the alveolar ridge dimen-
Dimensions sions of the posterior maxillary sextants in a split-mouth
study in 32 patients (mean age 55.9 ± 7.8 years) using spiral
The height of the posterior alveolar process has mainly been CT, with one side of the posterior maxilla fully edentulous
assessed in edentulous subjects during the planning of and the contralateral side dentate (first premolar to second
implant placement in the premolar and molar areas molar). The reduction of the bone width measured 1 mm
(Table 8.2) (Figs. 8.6, 8.7, and 8.8). Several studies have below the crest of edentulous sextants ranged from 2.8 mm
addressed the vertical dimension of the posterior maxilla. (first premolar) to 5.3 mm (first molar) compared to the con-
Ulm et al. (1993) evaluated the profile and bone volume of tralateral dentate sextants, whereas the reduction of the bone
78 maxillae in predefined areas. In the premolar-molar height ranged from 1.5 mm (first premolar) to 4.6 mm
region, the bone volume was found to be diminished up to (second premolar). Sinus pneumatization accounted for up to
80 % following tooth extraction. The main factors causing 46 % of reduced bone height.
such bone deficit were the remodeling of the alveolar crest Kopecka et al. (2012) analyzed the “subsinus” bone height
and a continuous expansion of the maxillary sinus into the unilaterally in panoramic radiographs of 583 edentulous
posterior alveolar process (pneumatization). The latter patients (mean age 55.4 ± 10.3 years). The mean bone height
appeared to be the most decisive factor regarding loss of in first premolars was 10.6 ± 3.8 mm, in second premolars
bone volume in the posterior maxilla, since, even in 5.9 ± 2.5 mm, in first molars 3.3 ± 2.2 mm, and in second
apparently wide and high crests, a thin bone plate of only molars 4.5 ± 2.4 mm. In 73.1 % of first molar sites, the subsi-
1 mm may remain below the floor of the maxillary sinus. nus bone height was <5 mm.
Güler et al. (2005) measured the height of the posterior A similar study was performed by de Souza et al. (2013) in
alveolar process in 173 panoramic radiographs of edentulous 122 patients (mean age 57.5 years, range 21–92 years) using
patients. The measurements were taken as the vertical dis- CBCT for measurement of bone height in 252 edentulous sites.
tance from the inferior border of the maxillary sinus to the The mean height measured at first and second premolar and
alveolar crest on the zygomatic vertical line. The mean dis- first and second molar sites was 13.3 mm, 7.7 mm, 5.0 mm and
tances in males were 7.8 ± 3.88 mm (range 0.3–18.1 mm) 5.1 mm, respectively. While the height in first premolar sites
and in females 8.2 ± 3.39 mm (range 1.8–17.6 mm). The dif- was never <5 mm, 54.1 % of first molar sites and 44.6 % of
ference was not statistically significant. second molar sites demonstrated a reduced bone height <5 mm.
Table 8.2 Summary of mean measurements reported for bone height (mm) of the posterior alveolar process
Dentate subjects Edentulous subjects
Premolar area – 5.9–13.3
Molar area – 3.3–5.1
138 8 Posterior Maxilla
Fig. 8.6 Representative ridge heights depicted in a sagittal CBCT Fig. 8.8 Buccolingual CBCT in the area of the left maxillary second
bisecting posterior alveolar process of left maxilla in a 35-year-old molar (note excellent ridge width but limited ridge height)
male
Fig. 8.7 Buccolingual CBCT in the area of the left maxillary second
premolar (note excellent ridge width but limited ridge height)
Root Positions Within the Posterior Alveolar Process 139
Root Positions Within the Posterior Alveolar Howe (2009) recorded the minimum distance from the
Process roots of maxillary first molars to their corresponding cortical
plates. Measurements were obtained 3 mm coronally to the
The knowledge of the horizontal position of the roots within socket apex using CBCT and gross dissection of 37 human
the alveolar process (Figs. 8.9 and 8.10) is helpful when sur- cadaveric maxillae. The mean distances for mesiobuccal roots
gical access to the roots is required (apical surgery, resection were 0.7 ± 0.7 mm (CBCT) and 0.6 ± 0.6 mm (dissection), for
of complete roots, surgical removal of teeth and roots). In distobuccal roots 1.1 ± 1.0 mm and 1.0 ± 1.0 mm, and for pala-
this section, positions and distances between root apices and tal roots 1.4 ± 1.1 mm and 1.4 ± 1.0 mm, respectively.
the alveolar process are presented while spatial relationships Kang et al. (2015) calculated the distances between the api-
between root apices and the maxillary sinus are discussed in ces of posterior maxillary teeth to the surface of the buccal
Chap. 9 (Maxillary Sinus). cortical plate in 132 Korean patients using axial CBCT images.
Eberhardt et al. (1992) assessed the distances between The mean distances were 2.24 mm for single-rooted first pre-
root apices of posterior maxillary teeth and their respective molars, 1.05 mm for buccal roots of first premolars, 5.15 mm
bone surfaces in 38 patients using CT. The following mean for palatal roots of first premolars, 3.82 mm for single-rooted
values were obtained: in first premolars 1.63 ± 0.44 mm for second premolars, 2.46 mm for buccal roots of second premo-
buccal and 5.42 ± 0.86 mm for palatal roots; in second pre- lars, 5.98 mm for palatal roots of second premolars, 3.00 mm
molars 3.16 ± 0.39 mm; in first molars 2.22 ± 0.39 mm for for mesiobuccal roots of first molars, 3.13 mm for distobuccal
mesiobuccal, 1.72 ± 0.62 mm for distobuccal, and roots of first molars, 12.16 mm for palatal roots of first molars,
3.01 ± 0.54 mm for palatal roots; and in second molars 4.99 mm for mesiobuccal roots of second molars, 3.99 mm for
4.25 ± 0.61 mm for mesiobuccal, 3.19 ± 0.69 mm for disto- distobuccal roots of second molars, and 11.28 mm for palatal
buccal, and 2.76 ± 0.61 mm for palatal roots. roots of second molars, respectively.
bPM1
pPM1
bPM1
pPM1
PM2
mbM1
PM2
dbM1
mbM1
pM1
pM1
dbM1
bM2
mbM2
pM2
pM2
dbM2
Maxillary Tuberosity A similar case report was published by Polat et al. (2007).
A private practitioner attempted to extract the right maxillary
The maxillary tuberosity is the most posterior part of the alveo- first molar in a 28-year-old male and he produced a fracture
lar process (Figs. 8.11 and 8.12). When the upper third molar of the tuberosity including all three molars. Another case
remains retained or impacted, it may occupy part of the tuber- report of a 52-year-old male patient described a severe sub-
osity. Cheung et al. (1998) evaluated 30 dry skulls of Chinese conjunctival and buccal hemorrhage following maxillary
origin with regard to the height and width of the tuberosity. The third molar extraction with fracture of the tuberosity
mean height of the tuberosity was 4.89 ± 1.87 mm (range 2.8– (Thirumurugan et al. 2013).
8.0 mm), and the mean width distal to the second molar was The etiological and predisposing factors were analyzed
21.1 ± 2.16 mm (range 15.7–26.2 mm). The mean distance by Chrcanovic and Freire-Maia (2011), publishing a litera-
from the lowest point of the tuberosity to the highest point of ture review concerning maxillary tuberosity fractures during
the pterygomaxillary junction measured 12.07 ± 1.99 mm extraction of upper molars. Among 14 factors listed, only 1
(range 8.9–19.0 mm). Apinhasmit et al. (2005) assessed the was anatomy-related, i.e., a large maxillary sinus with thin
height and width of the tuberosity in 55 dry skulls of Thai ori- walls and sinus extension into the maxillary tuberosity. In
gin. The mean height of the tuberosity was 7.45 ± 2.78 mm contrast, most of the predisposing factors were tooth or root
(range 1.2–14.0 mm), and the mean width distal to the second related including fusion of teeth, ankylosis, hypercemento-
molar was 20.38 ± 2.82 mm (range 12.4–27.1 mm). sis, elongated roots projecting into the sinus, and large,
A relatively rare complication considered in exodontia is divergent, or curved roots.
the fracture of the maxillary tuberosity (Figs. 8.13 and 8.14) The maxillary tuberosity has also been described as a pos-
that occurs in about 0.08–0.15 % (Chrcanovic and Freire- sible donor site for bone grafts to be used in conjunction with
Maia 2011). However, sequelae in conjunction with a frac- implant placement (ten Bruggenkate et al. 1992; Tolstunov
tured tuberosity may be severe. A case report in a 22-year-old 2009). While the amount of bone to be harvested from the
male described the fracture of the complete alveolar process maxillary tuberosity is limited, access and visibility are good
including all three erupted molars and the tuberosity during and morbidity is low compared with other intra- or extraoral
an attempt of extracting the first molar (Altug et al. 2009). donor sites of autogenous bone grafts.
M2
2 12.1 mm
PMF
GPF
1 4.9 – 7.5 mm
Maxillary LPF
tuberosity
PTPlp
Fig. 8.12 Lateral view of the right side of a dry skull showing reported
mean dimensions related to the maxillary tuberosity. 1 Height of tuber-
PTP osity, 2 distance from highest point of pterygomaxillary fissure to low-
est point of maxillary tuberosity. PMF pterygomaxillary fissure
Fig. 8.11 Occlusal view of the right maxillary tuberosity in a dry skull.
GPF greater palatine foramen, LPF lesser palatine foramen, M2 second
molar, PTP pterygoid process of sphenoid bone, PTPlp lateral plate of PTP
The Posterior Superior Alveolar Nerve and Artery 141
ION
ION
ION
Posterior Superior Alveolar Nerve infraorbital nerve in the pterygopalatine fossa either as a
single trunk (83.8 %) or as a thick nerve and multiple
The path and relation of the superior alveolar nerves were branches (16.2 %). After running downward and forward and
studied in 19 hemisectioned cadaveric heads by Heasman piercing the infratemporal surface of the maxilla, the PSAN
(1984). PSAN were found in all 19 specimens entering the either passed through a canaliculus in the posterolateral wall
infratemporal surface of the maxilla at various levels (range of the maxillary sinus (62.2 %), or it ran beneath the mucous
10–43 mm) above the most inferior point of the maxillary membrane of the sinus (37.8 %). In the latter cases the PSAN
tuberosity, either as three branches (5/19), two branches always closely accompanied a branch of the PSAA. The
(13/19), or a single branch (1/19). One of the branches of the main trunk of the PSAN was never found to pass outside the
PSAN usually accompanied the PSAA. In nine dissections, buccal cortex of the maxilla.
individual branches descended directly from the PSAN to
premolar and molar teeth, whereas in the remaining 10 spec-
imens a complex nerve plexus was observed. In 15 dissec- Posterior Superior Alveolar Artery
tions a PSAN could be traced anterosuperiorly to form a
direct communication with the ASAN (the latter descending The PSAA typically branches from the maxillary artery just as
inferomedially below the infraorbital foramen toward the it passes into the pterygopalatine fossa. In a study evaluating 20
piriform aperture). Moretto et al. (2005) studied 30 hemisec- hemisectioned maxillae, the PSAA and the infraorbital artery
tioned cadaveric heads. In 70 % two branches of the PSAN had a common trunk (Fig. 8.16) in 60 % of the specimens,
were present, in 20 % three branches, and in 10 % one branch. whereas in 40 % of the cases, the PSAA emerged directly from
Murakami et al. (1994) assessed 37 adult cadaveric heads the maxillary artery (Kqiku et al. 2013). The caliber (mean
regarding the PSAN after staining by whole-mount silver external diameter) of the PSAA after exiting from the maxillary
impregnation. The PSAN originated from the base of the artery was reported to be 1.6 ± 0.21 mm (range 1.3–2.0 mm),
IOA
MA
MSpw
PSAA
and the length of the PSAA measured on average 8.2 ± 3.62 mm inferior branches of the IOA. These anastomoses run superfi-
(range 4–16 mm) in 18 dissected hemimaxillae (Solar et al. cially to the bone surface of the maxillary sinus. Intraosseous
1999; Traxler et al. 1999). The same authors reported between anastomoses, also called the alveolar antral artery (Rosano
one and four intraosseous and one and two extraosseous et al. 2009), are formed by the alveolar branches of the PSAA
branches from the PSAA. In those studies, the PSAA and the and the ASAA and may run completely embedded in bone or
infraorbital artery formed a common trunk in 33 % of the cases. below the Schneiderian membrane (Ella et al. 2008). Usually,
The PSAA enters the posterior superior alveolar foramina 3-dimensional radiography depicts the bone channels of these
(Fig. 8.17) on the maxillary tuberosity and gives off dental and intraosseous vascular anastomoses (Figs. 8.21, 8.22, 8.23,
alveolar branches. The dental branches of this artery supply the 8.24, 8.25, 8.26, 8.27, 8.28, 8.29, 8.30, and 8.31). Ligation of
pulp tissue of the posterior maxillary teeth, and the alveolar an unusually wide (3 mm) intraosseous anastomosis was doc-
branches supply the periodontium, whereas superficial umented by Testori et al. (2010). The authors recommended
branches contribute to the maxillary gingivae. Dental and alve- ligation of such large vessels to avoid intra- and postoperative
olar branches also supply the maxillary sinus (Flanagan 2005; bleeding complications in sinus floor elevation procedures.
Ella et al. 2008). The PSAA can be encountered while aspirat- In cadaver studies, the intraosseous anastomosis is typi-
ing during infiltration anesthesia of the maxillary second or cally observed while the extraosseous anastomoses are less
third molar because it runs near the tuberosity (Flanagan 2005). frequently found (Table 8.3). In general, the anastomoses of
Others have divided the PSAA broadly into an intraosseous the PSAA and the branches of the infraorbital artery form a
branch, supplying the molars and the maxillary sinus, and an double arterial arcade in the posterior maxilla (Solar et al.
extraosseous branch, supplying the attached gingiva and 1999; Traxler et al. 1999; Kqiku et al. 2013). Sato et al.
mucosa of the buccal aspect of the posterior maxilla (Hur et al. (2010) investigated the course of the PSAA with CBCT and
2009). The intraosseous artery may run through a bony groove image reconstruction in 34 cadaveric hemimaxillae. The
or canal along the lateral wall of the maxillary sinus. PSAA ran in the posterolateral wall of the maxillary sinus
The PSAA usually has a vascular anastomosis (VA) with either in a canal-like structure (14.7 %), in a ditch-shaped
the ASAA or the IOA (Figs. 8.18, 8.19, and 8.20). Extraosseous tunnel structure (67.6 %), or in a fragmented structure
anastomoses are formed by the mucosal branches of the PSAA (17.6 %). Yoshida et al. (2010) using the identical study sam-
that connect with the mucosal branches of the ASAA or with ple of Sato et al. (2010) described the supply pattern of the
PSAF
VC
PPF
IOA
MA IOA
PSAA
IOA
ASAA
ANe
ANi
MSlw
Posterior Superior Alveolar Artery 145
iPM1
M2
IOC
CSin
VC
Maxillary sinus VC
Maxillary sinus
VC
VC
VC VC
VC
SR
pM1
MT
dbM1
M2
Fig. 8.21 Sagittal CBCT image showing multiple anastomotic bone Fig. 8.22 Coronal CBCT image showing submembranous location of
channels in the posterior left maxilla in a 42-year-old patient. M2 sec- intraosseous bone channel. CSin canalis sinuosus, IOC infraorbital
ond molar, MT maxillary tuberosity, VC vascular canals (bone canal, dbM1 distobuccal root of first molar, pM1 palatal root of first
channels) molar, SR sinus recessus with swelling of Schneiderian membrane, VC
vascular canals (bone channels)
146 8 Posterior Maxilla
Maxillary sinus
CSin
VC
VC
M3
M2
PM2 M1
PM1
CSin
VC
a b c
Fig. 8.25 Schematic illustration of coronal CBCT images showing membrane and the bony wall. (b) Vascular canal completely embed-
typical positions of the vascular canal within the lateral wall of the ded within the bony wall. (c) Vascular canal located lateral to the bony
maxillary sinus. (a) Vascular canal located between the Schneiderian wall
Maxillary sinus
VC
Periapical VC
lesion
Root remnant
PM2
M2
Fig. 8.26 The periapical radiograph of the right maxillary second
molar shows a periapical radiolucency (arrows) but also a prominent
curved dark line (arrowheads) projected over the maxillary sinus in a
52-year-old male
Maxillary sinus
IC
IM
VC
Periapical
lesion
M2
Fig. 8.29 A 3D rendering of CBCT images (inferolateral view) show-
ing a very broad intraosseous vascular canal (arrowheads) in the lateral
wall of the left maxillary sinus in a 67-year-old male
Fig. 8.28 The coronal CBCT image at the level of the mesiobuccal
root of the second molar shows a large vascular canal (intraosseous
anastomosis) in the lateral wall of the right maxillary sinus. IC inferior
concha, IM inferior meatus, M2 second molar, VC vascular canal
Orbit
IOC
ZB
Maxillary sinus
IC
Lateral wall
of maxillary sinus
VC
Fig. 8.31 Intraoperative view of the lateral wall of the maxillary sinus
following elevation of a full mucoperiosteal flap for sinus floor eleva-
tion. The broad intraosseous vascular anastomosis is clearly visible
Fig. 8.30 The coronal CBCT section exhibits the location of the vas- (arrowheads)
cular canal within the lateral wall of the left maxillary sinus. IC inferior
concha, IOC inferior orbital canal, SuP sulcus palatinus, VC vascular
canal, ZB zygomatic bone
The Os Zygomaticum 149
PSAA between the alveolar foramen and the premolar region the extraosseous VA, and between 10.5 and 99.4 % for an
and categorized it into three groups: (I) the PSAA ascended unspecified VA. Güncü et al. (2011) reported that the VA
toward the infraorbital foramen (17.6 % of specimens), (II) was detected in 61.3 % of females, but only in 29.6 % of
the PSAA descended to an area above the lowest border males. In contrast, Kim et al. (2011) reported significantly
of the maxillary sinus (53 %), and (III) the PSAA descended more VA in males (64 %) compared to females (40 %).
to the region below the floor of the maxillary sinus (23.5 %). Ilgüy et al. (2013) observed a VA significantly more fre-
In 5.9 % the pattern of the PSAA could not be categorized. quently in dentate (99.4 %) compared to edentulous
Mardinger et al. (2007) assessed the intraosseous VA in (75.9 %) patients.
104 patients with CT (208 sides). The bony canal formed a
concave arch with the most inferior site in the first molar area.
In 6.7 % of the sides, the canal had a diameter of 2–3 mm. The Size of the Vascular Anastomosis
canal diameter was significantly related to age, and the authors
concluded that the older the patient, the wider the canal. No The mean diameter reported in the literature averaged
correlation was found with gender, presence of teeth, or side. between 0.8 and 1.52 mm, with a maximum value of 3.8 mm
Jung et al. (2011) determined the position of the vascular (Table 8.3). Most researchers considered a VA diameter
canal in the lateral maxillary sinus wall at 207 sites with ≥2 mm a risk for intraoperative hemorrhage. In a radio-
CBCT. A predominantly intraosseous location was found in graphic study of 121 patients with CT, the mean diameter of
first premolar (69.2 %) and second molar sites (46.6 %), the VA was 1.3 ± 0.5 mm with a significant difference com-
whereas an “intrasinus” location was more common in sec- paring males (1.4 ± 0.4 mm) and females (1.2 ± 0.4 mm). No
ond premolar (45.7 %) and first molar sites (89.1 %). Overall, disparity was observed correlating the size of the VA with
the “intrasinus” location was the most frequent (63.8 %) fol- age and side (Güncü et al. 2011).
lowed by the intraosseous location (28.5 %). A superficial,
lateral location was infrequent (7.7 %).
A detailed study of the course of the PSAA was performed Location of the Vascular Anastomosis
by Hur et al. (2009) in 42 Korean cadaveric hemifaces utiliz-
ing dissections of 32 specimens that were injected with col- Conflicting data have been reported regarding the location
ored Latex, while the remaining 10 specimens were subjected of the VA with respect to the lateral wall of the maxillary
to routine histological analysis including decalcification, sinus (Table 8.3). While two studies (Güncü et al. 2011;
sectioning, and microscopy. Before entering the foramen (or Ilgüy et al. 2013) predominantly found an intraosseous
foramina) above the maxillary tuberosity, the PSAA divided course of the VA (68.2 %, 71.1 %), a third study (Jung et al.
into an extra- and intraosseous branch. The intraosseous 2011) reported that the VA was most commonly situated
branch was found to form an anastomosis with the ASAA in along the inner aspect of the lateral wall (63.8 %). Various
all specimens, and the course in the lateral wall of the maxil- studies have measured the distance from the VA to the alve-
lary sinus was either straight (78.1 %) or U-shaped (21.9 %). olar crest with large variations of the reported mean values
Nicolielo et al. (2014) assessed CBCT scans of 100 (9.6–31.7 mm) (Table 8.4). The likely reason for these dis-
patients and divided superior alveolar canals (SAC) into crepancies is that the distances were either assessed at dif-
anterior (ASAC, originating from the infraorbital canal) ferent sites (tooth positions), of intra- or extraosseous VA, or
and posterior (PSAC) canals. ASAC were observed in in dentate, partially dentate or edentulous posterior maxil-
100 % of the cases, and PSAC in 73 %. The mean diameter lae. Another landmark from where to measure the distance
of ASAC was 0.9 ± 0.27 mm (range 0.4–1.8 mm) and of to the VA is the floor of the maxillary sinus. The reported
PSAC 0.83 ± 0.27 mm (range 0.3–1.9 mm). The distances mean values for that distance ranged between 5.9 and
from the ASAC to the alveolar crest ranged between 9.1 10.3 mm (Table 8.4).
and 44.6 mm and from the PSAC to the alveolar crest
between 2.4 and 32.3 mm.
The Os Zygomaticum
Frequency of Vascular Anastomosis The zygomatic bone (zygoma, malar bone, or malar buttress)
is a protruding structure that forms the main contour of the
Many cadaver and clinical studies have assessed the pres- midface (Kim et al. 2013) (Figs. 8.32 and 8.33). The zygo-
ence of a VA between the ASAA and the PSAA and reflect matic buttress is a strong bony pillar that provides pressure
a wide range of frequency and pattern (Table 8.3). The fre- absorption and transduction in the facial skeleton (Gellrich
quencies reported for VA detection range between 90 and et al. 2007). The os zygomaticum has frontal and temporal
100 % for the intraosseous VA, between 33.3 and 100 % for processes and an orbital surface. Medially and inferiorly it
Table 8.3 Frequency and diameter (mm) of vascular anastomosis (VA) in the posterior maxilla (anterolateral wall of the maxillary sinus [MS])
150
1,3
Kim et al. (2011) 200 patients (CT) (age 400 sides (200 males, All: 52 % 1.52 ± 0.47 – – Significant
range 45–65 years) 200 females) Males: (0.3–2.7) difference
1
64 % <1 (13.9 %) 1–2
Females: 240 % (64.9 %)
>2 (21.2 %)
Posterior Maxilla
Rosano et al. (2011) 100 patients (CT) 200 sides 47 % <1 (55.3 %) – – –
(mean age 53.5 years, 1–2 (40.4 %)
range 29–78 years) >2 (4.3 %)
Temmerman et al. (2011) 144 patients (multislice 288 sides (156 males, 49.5 % 1.4 ± 0.55 – – –
CT) (mean age 132 females) (128 (0.6–3.8)
58.2 years, range edentulous, 160
22–79 years) partially dentate)
The Os Zygomaticum
Ilgüy et al. (2013) 135 patients (CBCT) 270 sides (116 All: 89.3 % 0.94 ± 0.26 – Intraosseous: *Total is 89.3 %
1,2
(mean age edentulous, 154 dentate) Edentulous: (0.4–1.7) *71.1 % Significant
1
43.1 ± 17.6 years) 75.9 % ≤1 (68.9 %) Inner aspect of difference
Dentate: wall:
2
99.4 % *13 %
Outer aspect of
wall:
*5.2 %
Kang et al. (2013) 150 patients (CBCT) 135 sides – 1.18 ± 0.45 mm – Intraosseous: –
(mean age 49.4 years, Males: 64.3 %
range 23–86 years) 1.24 ± 0.44 mm Inner aspect of
Females: wall:
1.07 ± 0.43 mm 29.1 %
Outer aspect of
wall:
6.6 %
Kqiku et al. (2013) 10 cadaveric heads 20 sides Extraosseous: – – – –
100 %
Intraosseous:
90 %
Apostolakis and Bissoon 156 patients (CBCT) 312 sides 82 % 1.1 ± 0.4 – – –
(2014) (mean age 48 years, (0.2–2.6)
range 19–88 years)
Anamali et al. (2015) 254 patients (CBCT) 508 sides Right side: 94.4 % – – – –
(mean age 57.6 years, Left side: 91 %
range 20–87 years)
151
Table 8.4 Distances (mm) from vascular anastomosis (VA) in the lateral wall of the maxillary sinus (MS) to adjacent anatomical structures
152
contacts the os maxilla, superiorly the frontal bone, and poste- the sinus slot technique which allows a more lateral position-
riorly the sphenoid and temporal bones. The posterior side of ing of the implant head and reduces sinus complications, and
the zygoma also borders the infratemporal fossa. The temporal (III) the extrasinus technique with implant insertion into the
process of the zygoma forms the anterior portion of the zygo- lateral wall of the maxillary sinus and into the zygomatic
matic arch. Two foramina are usually present including the bone (Candel et al. 2012a). An extremely rare complication
zygomaticofacial and the zygomaticotemporal foramina deliv- of intracerebral penetration by a zygomatic dental implant
ering nerves with corresponding names. However, recent stud- was reported by Reychler and Olszewski (2010). The zygo-
ies of zygomatic bones described up to four zygomaticofacial matic implant passed through the left maxillary sinus and the
foramina as well as up to four zygomaticotemporal foramina left pterygopalatine fossa between the maxillary nerve and
including complex patterns of the bony canals within the the internal jugular vein. The intracerebral penetration was
zygomatic bone (Loukas et al. 2008; Kim et al. 2013). situated in the left temporal fossa between the foramen
The dimensions of 30 left side cadaveric zygomatic bones rotundum and foramen ovale. No clinical signs or symptoms
were assessed with spiral CT by Nkenke et al. (2003). The of impairment of the cranial nerves were apparent, but the
mean anteroposterior length of the zygomatic bone was 47-year-old female patient complained of severe persistent
25.4 mm in females and 24.9 mm in males. The mediolateral headache.
thickness was 7.6 mm in females and 8.0 mm in males. The The zygoma or the zygomatic buttress has also been used,
mean estimated implant length within the zygomatic bone although less frequently compared to other intraoral sites, as
was 14.0 mm for females and 16.5 mm for males. None of a donor site of autogenous bone grafts (Kainulainen et al.
the gender differences reached a statistically significant 2002; Held et al. 2005). A clinical study documented 32
level. In a similar study, nine cadaveric heads (18 sides) were patients with bone grafts taken from the zygoma in conjunc-
evaluated with CT regarding the size of the zygomatic bone tion with implant placement (Kainulainen et al. 2005). A
(Kainulainen et al. 2004). The mean height, length, and trephine bur, a round bur, or an implant-twist drill was used to
thickness were 21.2 ± 2.7 mm, 32.3 ± 4.6 mm, and harvest bone from the anterior aspect of the zygomatic bone.
9.0 ± 1.7 mm, respectively. The mean height of the zygoma The mean volume of the harvested zygomatic bone graft was
measured during bone harvesting from the cadaveric heads 0.9 ± 0.3 mL. No sensitivity changes regarding the zygomati-
was 22.5 ± 2.4 mm, hence similar to the CT-assessed height cofacial nerves were reported. However, in 34 % a 2- to 5-mm
of 21.2 ± 2.7 mm. large perforation into the maxillary sinus was observed
Zygoma implants (Figs. 8.34 and 8.35) are a reconstruc- (Kainulainen et al. 2005). The advantages of the zygomatic
tive technique for prosthetic rehabilitation of patients with buttress region as a donor site of bone grafts include easy
extensive defects of the maxilla caused by tumor resection, access, excellent visibility, and strong bony structure.
trauma, or congenital defects (Att et al. 2009; Aparicio Moreover, no muscles have to be detached in that area.
2011). They are also indicated in cases of severe resorption According to Gellrich et al. (2007) a bone graft of
of the maxilla in free-end situations and complete edentulism. 1.5–2 cm2 taken from the caudal zygomatic buttress zone
Several groups have reported excellent outcomes of implants will not compromise the strength of the lateral midface
placed into the zygomatic bone (Parel et al. 2001; Aparicio frame, in the case of an otherwise non-traumatized facial
et al. 2006). Usually, a 35- to 52.5-mm-long implant is skeleton. Limiting factors are the mucous membrane of the
inserted from the palatal aspect of the resorbed maxilla in the adjacent maxillary sinus and the close relationship to the
region of the second premolar through the maxillary sinus infraorbital foramen. However, direct visualization of the
into the compact bone of the zygoma (Rossi et al. 2008). infraorbital region allows nerve identification and preserva-
Candel et al. (2012a) reviewed 16 studies (follow-up tion during bone graft harvesting (Gellrich et al. 2007).
1–10 years) published from 1987 to 2010 with a total of 941 A recent CBCT-based radiographic study of 698 patients
zygomatic implants placed in 486 patients with atrophic pos- has documented pneumatization of the zygomatic bone to
terior maxilla. The weighted success rate was 97.1 %. The occur in 3.3 % of evaluated individuals and in 2.8 % of
most frequent complication was maxillary sinusitis (range assessed zygomatic bones (Nascimento et al. 2015). Of
1.9–18.4 %). The reviewers described three different tech- those cases, 30.5 % were unilateral and 69.5 % bilateral. All
niques: (I) the classic technique exposing the anterolateral presented a multilocular pattern. Pneumatization of the
portion of the zygomatic bone and creating a bony window zygomatic bones was neither correlated with gender nor
in the maxillary sinus to visualize the implant trajectory, (II) with age.
156 8 Posterior Maxilla
CM
CP
PG
ZFS
ZFF
ZTS
ZMS
Fig. 8.33 Outline of the zygomatic bone (dotted red line). ZFF
zygomaticofacial foramen, ZFS zygomaticofrontal suture, ZMS
zygomaticomaxillary suture, ZTS zygomaticotemporal suture
The Os Zygomaticum 157
ZFF
PPF
MT
The pyramidal process of the palatine bone is located The pterygoid process is the most inferior part of the sphe-
between the maxillary tuberosity and the pterygoid process noid bone (Figs. 8.38 and 8.39). The process consists of two
of the sphenoid bone (Figs. 8.36 and 8.37). Anatomically, it bone plates (medial and lateral) that are fused anteriorly (see
appears as it is fused to the anterior surface of the pterygoid Chaps. 12 and 25). The development of surgical techniques
process. Only very few studies have studied the pyramidal using the pterygoid process as a point of bone anchorage for
process. Lee et al. (2001) assessed the dimension and shape oral implants has generated considerable interest in this ana-
of the pyramidal process in 54 dry Korean edentulous skulls. tomical feature.
The mean height of the pyramidal process was 13.1 ± 2.8 mm Implant placement into the pterygoid region of the poste-
(range 8.3–21.4 mm), the mean anteroposterior distance rior maxilla was first reported by Tulasne (1992). Ridell
was 6.5 ± 1.1 mm (range 3.3–9.7 mm), and the mean medio- et al. (2009) reported no loss of 22 implants placed into the
lateral distance was 9.5 ± 1.7 mm (range 4.2–11.8 mm). The maxillary tuberosity region with a mean follow-up of
most common shape of the pyramidal process was the right- 8 ± 3.4 years. Candel et al. (2012b) reviewed 13 studies pub-
angled triangle from the lateral as well as from the posterior lished from 1992 to 2009 (follow-up 6 months to 10 years)
aspect. with 1053 pterygoid implants placed in 676 patients. The
MT MT
PPP PPP
LPF
LPF
PTP PTP
Clinical Relevance of the Posterior Maxilla 159
PPP
Clinical Relevance of the Posterior Maxilla
PTP
PMF
PTP
PTPlp PMF
PTPmp
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Maxillary Sinus
9
The maxillary sinus (MS) is a dominant bilateral anatomical and the posterior lateral nasal artery (Rosano et al. 2009).
structure in the posterior maxilla and midface (Figs. 9.1, 9.2, 9.3, The posterior superior alveolar and infraorbital arteries
and 9.4). The MS is also referred to as the “antrum of Highmore” (Chaps. 6 and 8) typically are direct branches of the third
since it was first described in detail by the British surgeon (pterygopalatine) portion of the maxillary artery. The poste-
Nathaniel Highmore (1613–1685). The function of the MS is not rior lateral nasal artery is a branch of the sphenopalatine
clearly understood, but several functions have been attributed to artery that also forms as the termination of the maxillary
it including adding resonance to the voice, some degree of olfac- artery (Flanagan 2005). After passing through the spheno-
tory function, warming and humidifying the inspired air, and palatine foramen, the sphenopalatine artery divides into the
reducing the weight of the skull (van den Bergh et al. 2000). posterior lateral and posterior septal branches (Figs. 9.9 and
The MS is the largest of all paranasal air sinuses. The MS 9.10). The posterior lateral branch can be found close to, or
occupies the body of the os maxilla. The MS exhibits a wide within, the lateral wall of the nasal cavity (medial wall of the
range of anatomical variation that is relevant to diagnostic antrum). The diameter of this artery increases as it proceeds
radiology. At birth the MS is present but small (3 × 6 × 8 mm), anteriorly, possibly reflecting anastomoses with the termi-
whereas in adults the MS is large and pyramidal in shape (du nals of the facial artery or other nasal arteries as well as the
Toit and Nortjé 2003). The lateral wall of the nasal cavity anterior and posterior ethmoidal arteries. The posterior lat-
forms the base of the pyramid-shaped MS, and the apex of eral branch also ramifies, and these small branches spread
the MS, also referred to as the lateral canthal tip, projects over the conchae and meatus and supply the sinuses of the
laterally to the zygomatic bone (Fig. 9.5). The floor of the corresponding side, including the posterior and medial wall
MS usually consists of a thin bony plate covering the root of the MS (Flanagan 2005).
apices of the posterior teeth. The roof of the MS is formed by The proximity of the floor of the MS to the posterior teeth is
the bony floor of the orbit. The MS typically displays several an important aspect of dentistry regarding anatomical, physio-
recesses into neighboring structures including the alveolar logical, and pathological characteristics of the MS (Figs. 9.11
recess (or multiple recesses) expanding into the posterior and 9.12). An array of clinical dental conditions may inflict
alveolar process of the os maxilla, the zygomatic recess pro- upon the MS: periapical pathosis and cysts, profound periodon-
jecting into the zygomatic process of the os maxilla, and the tal disease, retained or impacted teeth, displacement of root
orbital recess located in the medial orbital process of the os fragments or teeth into the antrum, oroantral communication
maxilla (Fig. 9.6). Occasionally, a pterygopalatine recess is and fistula, and dislodgement of foreign materials (root canal
present in the posteromedial aspect of the MS approaching medicaments and filling materials, dental implants) (Figs. 9.13,
the pterygopalatine fossa. Recently, Chan et al. (2013) char- 9.14, 9.15, 9.16, 9.17, 9.18, and 9.19). Further, benign and
acterized a palatonasal recess along the palatal wall of the malignant tumors may spread into or arise from the MS simu-
maxillary sinus extending below the nasal cavity (Fig. 9.7). lating odontogenic infections (Bornstein et al. 2008).
The ostium of the sinus opens into the middle meatus at In exodontia, the close relationship between the roots of
the posterior aspect of the semilunar hiatus of the lateral wall premolars and molars and the floor of the MS is a constant
of the nasal cavity. Since other paranasal air sinuses (frontal challenge. In implant dentistry, the pneumatization of the
sinus, anterior ethmoidal cells) drain into that region, it is also posterior alveolar process, the presence and type of antral
called the ostiomeatal complex (Wani et al. 2009) (Fig. 9.8). septa, the width of the lateral wall, and the configuration of
The MS is supplied by three primary arteries including the inferior portion of the MS are important issues to
the posterior superior alveolar artery, the infraorbital artery, consider.
MSpw
MSpw
PPF
MO
UP
NS ZB
Maxillary Maxillary
sinus VC sinus
IC
MSmw
VC
PTP
MT
Fig. 9.2 Coronal CBCT image of the left maxillary sinus in a 77-year-
old female. IC inferior concha, MO maxillary ostium, MSmw medial Fig. 9.3 Sagittal CBCT image of the left maxillary sinus. MT maxil-
wall of maxillary sinus, NS nasal septum, UP uncinate process, ZB lary tuberosity, PPF pterygopalatine fossa, PTP pterygoid process, VC
zygomatic bone vascular canal
9 Maxillary Sinus 165
MSaw
LD
IOC MSaw
MO
MSlw ZB
EC MS
EC
EC Fig. 9.5 Illustration of the inverted pyramidal shape and location of the
maxillary sinus
Fig. 9.4 Axial CBCT image of the left maxillary sinus. MSaw anterior
wall of maxillary sinus, EC ethmoidal cells, IOC infraorbital canal, LD
lacrimal duct, MO maxillary ostium, MS maxillary sinus, MSlw lateral
wall of maxillary sinus, ZB zygomatic bone
IC
MSmw
MSor
FS
EC EC Orbit
EC
MO
MiM
IC Maxillary
sinus
AEA
PEA
SPA
PSB
SPF
PLB
DPA PSB
NPA
GPA GPA
Fig. 9.9 Illustration of the sphenopalatine artery and its branches. AEA artery, PLB posterior lateral branch of SPA, PSB posterior septal branch
anterior ethmoidal artery, DPA descending palatine artery, GPA greater of SPA, SPA sphenopalatine artery, SPF sphenopalatine foramen
palatine artery, NPA nasopalatine artery, PEA posterior ethmoidal
9 Maxillary Sinus 167
SPA
SC
MC PLB
PSB
IC
IC
Fig. 9.12 Endoscopic image during antrostomy showing floor of max-
illary sinus with the root tips of the second and third molars (arrow-
heads) protruding into the sinus cavity. A healthy mucosa can be seen
with distinct thin blood vessels
HP/
NFl
M3
M2
M1
Fig. 9.11 Sagittal CBCT image showing the root tips of the left second
and third maxillary molars (arrowheads) protruding into the sinus cav-
ity. Root canal filling material (arrow) had been introduced into the
sinus cavity above the first molar requiring antrostomy for foreign
material removal. M1 first molar, M2 second molar, M3 third molar
168 9 Maxillary Sinus
Fig. 9.14 Endoscopic view of the displaced root fragment during root
removal via antrostomy
Fig. 9.16 Sagittal CBCT showing a dental implant that was dislodged
into the right maxillary sinus upon implant placement using the osteo-
tome technique in a 57-year-old female
*
*
*
Fig. 9.15 Sagittal CBCT view of right maxillary sinus with displaced
palatal root (arrow) of second molar into the maxillary sinus (note
severe swelling [*] of the sinus mucosa)
Fig. 9.17 Coronal view shows the dislodged implant within the swol-
len sinus mucosa
Radiography of the Maxillary Sinus 169
Radiography of the Maxillary Sinus the proximity of the root tip to the radiographic floor of the
MS. However, in this subset of cases, perforation of the MS
Due to the proximity of the posterior teeth to the MS, radiog- actually occurred only in 14.8 %, whereas it also occurred in
raphy of their spatial relationship is extremely important. 11.1 % of cases without such prediction. The authors con-
While periapical radiographs may depict the floor of the cluded that panoramic radiography is not a reliable method
sinus, visualization of the MS in toto is not possible. to predict the likelihood of sinus involvement during the
Panoramic and occipitomental radiography (Water’s view) extraction of posterior maxillary teeth.
yields a good overview of the bilateral maxillary sinuses, but Teke et al. (2007) assessed gender prediction by measur-
detailed observations are limited due to overlap of anatomi- ing the size of the MS in CT scans of 127 patients (65 males
cal structures. Only three-dimensional imaging techniques and 62 females). The discriminative analysis showed that the
(MRI, CT, CBCT) provide accurate depictions of the spatial accuracy of sinus measurements, i.e., the ability of the sinus
relationships and critical anatomical details of the MS. size to identify gender, was 69.4 % in females and 69.2 % in
Nedbalski and Laskin (2008) evaluated the use of pan- males. The authors concluded that CT measurements of MS
oramic radiography to predict possible MS membrane perfo- may be useful to support gender determination in forensic
ration during dental extraction. Possible exposure of the MS medicine; however, with a relatively low-accuracy rate of
was predicted in 27 out of 72 extractions (37.5 %) based on less than 70 %.
170 9 Maxillary Sinus
Volume and Size of the Maxillary Sinus area. The posterior limit of the MS was located in 94 % in
the third molar/maxillary tuberosity area and in 6 % in the
Several cadaver and CT studies have measured the dimen- second molar area.
sions of the MS (Table 9.1). The mean length of the MS Gosau et al. (2009) examined 65 cadaveric heads (130
reported in the literature ranged between 28.9 and sinuses) with regard to the real ventilated volume by measur-
47.6 mm, the mean height between 30.0 and 43.7 mm, and ing the water filled into the MS. The mean volume was
the mean width between 9.3 and 35.3 mm. Hence, the 12.5 mL (range 5–22 mL). A comprehensive analysis of the
greatest dimension of the MS is the length and the shortest size of the MS was performed by Sahlstrand-Johnson et al.
dimension is the width. The mean calculated volume of the (2011). The CT scans of 60 consecutive patients (mean age
MS ranged between 10.5 and 18 cm3 (mL). Occasionally, 40 ± 14 years) were studied. The mean anteroposterior length
the MS may present an unusual extension with the anterior of the MS was 35 ± 5 mm, the mean craniocaudal height was
border of the MS approaching the facial midline (Figs. 9.20, 31.3 ± 5 mm, and the mean mediolateral width was
9.21, and 9.22). 23.4 ± 4 mm. The mean volume of the MS was 15.7 ± 5.3 cm3
Uchida et al. (1998a) studied the dimensions of 59 sinuses and significantly larger in males than in females. No age or
in cadaveric heads after filling the antrum with silicone den- side effects were observed.
tal impression material. The mean volume of the MS was An even more detailed analysis of the maxillary sinus
11.3 ± 4.60 cm3. When the sinus-lift procedure was simu- width was reported by Chan et al. (2014). The authors
lated, inferior mean sinus volumes were 3.51 ± 1.23 cm3 for evaluated 422 edentulous sites in 320 subjects (mean age
a 15-mm sinus floor elevation and 5.66 ± 1.71 cm3 for a 50.1 years) using coronal CBCT images. The mean width at
20-mm sinus floor elevation. No significant differences were the inferior boundary (on an average of 2.3 mm above the
noted in any measurements (length, height, width, and vol- sinus floor) was 9.0 ± 2.8 mm and at the superior boundary
ume of MS) based on side, gender and age. (15 mm from the alveolar crest) 16.0 ± 4.4 mm. Overall, the
Kim et al. (2002) assessed the size and volume of the MS width was greater at molar than at premolar sites. In addi-
in 33 hemisectioned Korean cadaveric heads using CT and tion, the sinus width was greater at superior measurement
three-dimensional reconstruction of obtained images. The level and at sites with more severely resorbed ridges, given
maximum length, height, and width were measured per the same measurement level. The authors also presented a
sinus comparing male and female specimens. All measure- classification based on sinus width with regard to sinus floor
ments were larger in males than in females. Using 24 sides elevation: at the inferior boundary, the sinus width was clas-
and reformatted panoramic views, the mesial and distal sified as narrow (<8 mm), average (8–10 mm), or wide
extension of the MS was evaluated. In 58 % the anterior (>10 mm), whereas at the superior boundary, it was classi-
limit of the sinus was located in the first premolar area, in fied as narrow (<14 mm), average (14–17 mm), or wide
33 % in the canine area, and in 8 % in the second premolar (>17 mm).
Volume and Size of the Maxillary Sinus 171
Table 9.1 Dimensions (mm) and volume (cm3) of the maxillary sinus (MS)
Length of Volume of
Authors Study material N MS Height of MS Width of MS MS Comments
Ariji et al. 107 patients (CT) 15 children/adolescents 33.8 ± 3.3 – 30.1 ± 4.0 – –
(1996) (mean age (age <20 years) (27.6–38.0) (23.5–36.0)
46.5 years, range 92 adults (age 35.6 ± 4.7 – 27.0 ± 6.0 – –
4–94 years) ≥20 years) (16.0–47.6) (9.7–41.4)
Uchida 32 cadaveric 59 sinuses (36 males, 23 All: All: All: All: –
et al. heads (casts of females) 30.1 ± 5.65 34.6 ± 7.71 25.4 ± 5.71 11.3 ± 4.60
(1998a) MS using dental Males: Males: Males: Males:
impression 30.9 ± 5.56 35.9 ± 7.43 26.2 ± 6.19 11.8 ± 4.75
material) Females: Females: Females: Females:
28.9 ± 5.68 32.6 ± 7.89 24.0 ± 4.65 10.5 ± 4.33
Kim et al. 33 hemisectioned 19 males All: All: All: All: Volume given as
(2002) Korean cadaveric 14 females 39.3 ± 4.2 37.1 ± 5.6 32.6 ± 6.5 15.1 ± 6.2 mL
heads Males: Males: Males: Males:
40.7 ± 4.5 39.4 ± 5.8 35.3 ± 6.9 18.0 ± 6.2
Females: Females: Females: Females:
37.4 ± 3.0 34.0 ± 3.5 28.9 ± 3.5 11.1 ± 3.4
Teke et al. 127 patients (CT) 65 males Right side: Right side: Right side: – All measurements
(2007) (mean age NA) 47.6 ± 6.44 42.6 ± 7.95 27.2 ± 5.46 in males were
Left side: Left side: Left side: significantly
47.2 ± 6.54 43.7 ± 7.78 26.9 ± 5.52 greater than those
62 females Right side: Right side: Right side: – in females
45.1 ± 4.63 37.8 ± 5.69 24.4 ± 3.61
Left side: Left side: Left side:
43.6 ± 4.40 37.6 ± 6.04 24.3 ± 3.99
Gosau et al. 65 cadaveric 130 sinuses – – – 12.5 (5–22) Volume given as
(2009) heads mL
Uthman 88 patients (CT) 43 males Right side: Right side: Right side: – All measurements
et al. (2011) (age range 39.3 ± 3.8 43.4 ± 4.8 24.7 ± 4.0 in males were
20–49 years) Left side: Left side: Left side: significantly
39.4 ± 3.7 45.1 ± 4.1 25.6 ± 4.4 greater than
45 females Right side: Right side: Right side: – in females
36.9 ± 3.8 39.9 ± 5.2 22.7 ± 3.2
Left side: Left side: Left side:
37.0 ± 4.0 40.0 ± 4.8 23.0 ± 4.0
Sahlstrand- 60 patients (CT) 56 male sinuses Right side: Right side: Right side: Right side: –
Johnson (mean age 36 ± 3 34 ± 5 25 ± 4 18 ± 6 (9–32)
et al. (2011) 40 years, range (31–46) (27–43) (18–34) Left side:
18–65 years) Left side: Left side: Left side: 18 ± 7 (7–34)
35 ± 4 33 ± 5 25 ± 5
(26–43) (21–43) (14–33)
64 female sinuses Right side: Right side: Right side: Right side: –
35 ± 3 30 ± 3 23 ± 3 14 ± 3 (5–19)
(27–41) (20–35) (12–28) Left side:
Left side: Left side: Left side: 15 ± 4 (7–21)
34 ± 4 30 ± 3 23 ± 3
(27–40) (24–34) (16–30)
Chan et al. 320 patients Residual ridge height – – At 10 mm: – Data were grouped
(2014) (CBCT) (mean <4 mm (85 sites) 14 ± 3.5 according to
age 50.1 years, At 15 mm: residual ridge
range 17.6 ± 4.3 height, tooth site,
38–74 years) Residual ridge height – – At 10 mm: – and different
≥4 mm and <7 mm (167 12.2 ± 3.2 vertical levels from
sites) At 15 mm: the crest
16.5 ± 4.3
Residual ridge height – – At 10 mm: –
≥7 mm and <10 mm 9.3 ± 3.0
(170 sites) At 15 mm:
14.6 ± 4.1
(continued)
172 9 Maxillary Sinus
* *
pPM1
IC
pPM1
IC
MSa
NS
NPC
MSa
C C
MSa MSa
Bone
lesion
LI
LI
Fig. 9.22 The axial CBCT view shows the medial extension of the
maxillary sinus behind the canine (left side) and even behind the lateral
incisor (right side). C canine, LI lateral incisor, MSa anterior extension
of maxillary sinus, NPC nasopalatine canal, pPM1 palatal root of first
premolar
Fig. 9.21 The coronal CBCT depicts the unusual bilateral extension of
the maxillary sinus below the nasal aperture. IC inferior concha, MSa
anterior extension of maxillary sinus, NS nasal septum
Hypoplasia of the Maxillary Sinus 173
Hypoplasia of the Maxillary Sinus Meyers and Valvassori (1998) studied 400 CT scans of
patients undergoing endoscopic sinus surgery regarding ana-
In a normal-sized MS, the floor of the sinus is located below tomic variations of the paranasal sinuses. Since hypoplasia of
the level of the nasal cavity. In contrast, in hypoplastic MS, the MS predisposes to orbital penetration during endoscopic
its floor is situated above the floor of the nasal cavity sinus surgery, one of the study objectives was to determine
(Figs. 9.23, 9.24, 9.25, 9.26, 9.27, 9.28, and 9.29). The fre- the frequency of MS hypoplasia. This variation was present in
quency given for sinus hypoplasia in the literature ranges 4 % of the cases. In hypoplastic MS, the medial wall of the
between 4 and 5 %. Bolger et al. (1990) classified sinus sinus was displaced lateral to the medial wall of the orbit with
hypoplasia into three types: (I) mild hypoplasia with well- compensatory enlargement of the nasal cavity. A similar fre-
developed infundibular passage and a normal uncinate pro- quency of cases (4.6 %) with sinus hypoplasia was observed
cess, (II) significant hypoplasia with ill-defined infundibular by Selcuk et al. (2008) in CT scans of 330 patients. The
passage and a hypoplastic or absent uncinate process, and authors also described accompanying conditions such as
(III) profound hypoplasia represented by a shallow cleft in orbital enlargement, bony thickening of the sinus wall, unci-
the lateral nasal wall and absence of the uncinate process. nate process anomaly, and canine fossa elevation.
IOC
MidC
Maxillary
sinus Maxillary
sinus
CSin
IC
Periapical
lesion
Fig. 9.23 Coronal CBCT view of a hypoplastic maxillary sinus in a Fig. 9.24 The sagittal CBCT shows that the hypoplastic maxillary
23-year-old male. CBCT images were taken to assess a pathology asso- sinus is located below the orbit but remains well above the roots of the
ciated with the palatal root of the first maxillary molar. CSin canalis posterior teeth
sinuosus, IC inferior concha, IOC infraorbital canal, MidC middle
concha
174 9 Maxillary Sinus
MidC
MidC
Maxillary MS
sinus
IC IC
IC IC
Maxillary
sinus MS
PTPlp PTPlp
PTPmp PTPmp
Fig. 9.25 Coronal CBCT image exhibiting a hypoplastic maxillary
sinus on the left side in a 67-year-old male. IC inferior concha, MC
middle concha, MS maxillary sinus
Pneumatization
follow-up time of 6–67 months. As expected, pre-extraction membrane elevation on the medial wall of the maxillary
sinus expansion did not differ comparing the same left and sinus, thus increasing the risk of membrane perforation.
right dentate posterior sites in the control group Ananda et al. (2015) evaluated the presence and location
(−0.10 ± 1.05 mm). Post-extraction radiographs demon- of a recess of the maxillary sinus in 60 maxillary first molar
strated a mean inferior expansion of the sinus of sites using CBCT. In 18.3 %, the floor of the maxillary sinus
1.83 ± 2.46 mm. This difference was statistically significant was located above the apices. However, in 71.7 %, the maxil-
compared to the pre-extraction difference. No gender effect lary sinus extended downwards between the buccal and pala-
was noted. The largest inferior sinus expansion was observed tal roots. In 10 %, a sinus recess was observed at the buccal
after extraction of second molars (2.91 ± 2.61 mm) and in a aspect of the buccal roots, whereas a sinus recess palatal to
pre-extraction situation with a superiorly curved sinus floor the palatal root was never detected. Similar findings were
(5.27 ± 1.29 mm). reported by Kang et al. (2015) who assessed coronal CBCT
Chan et al. (2013) assessed the palatonasal recess of the images of 132 Korean patients for the lowest point of the
maxillary sinus on coronal CBCT images in 274 edentulous maxillary sinus relative to the maxillary molar roots. In first
sites of 225 individuals (mean age 49.2 years, range molars, the lowest point was located in 5.7 % buccal to the
38–74 years). The palatonasal recess was defined as the buccal roots and in 94.3 % between the buccal and palatal
intersection point of two imaginary lines following the lower roots. In the second molars, the corresponding figures were
part of the lateral nasal wall and the palatal wall of the maxil- 18.5 and 81.1 %. In 0.4 %, the lowest MS point was posi-
lary sinus. The mean angulation of the palatonasal recess tioned palatal to the palatal root.
was 109.8° ± 25.3° in the second premolar sites, 121.6° ± 22.1° Excessive and multiple extensions of the paranasal
in the first molar sites, and 144.9° ± 23.1° in the second molar sinuses including the maxillary sinus, sphenoid sinus, and
sites with significant differences among the sites. Risk sites frontal sinus were recently documented in a case report
with an angle <90° were more frequent in second premolar (de Oliveira et al. 2013). With regard to the maxillary
sites (15 %) compared to first (8.2 %) and second molar sites sinus, the patient presented bilateral palatal extensions
(2.4 %). The authors speculated that the latter cases with an below the nasal cavities and the extensions reached the
acute angle of the palatonasal recess might complicate sinus midline of the palate.
Maxillary
sinus
*
*
pM2
dbM2 *
Fig. 9.31 Coronal CBCT image of the right maxillary second molar
shows radiolucencies associated with the distobuccal and palatal roots
in a 52-year-old male (dotted lines represent sections of Figs. 9.32 and
9.33). dbM2 distobuccal root of second molar, pM2 palatal root of sec-
ond molar
Dimensions of the Maxillary Sinus: Walls 177
on coronal CBCT images of 74 patients. The mean width of Angle of Sinus Walls
the cortex was 0.86 ± 0.22 mm with no gender difference.
Kwak et al. (2010) assessed the thickness of the posterior The angle between the buccal and palatal alveolar walls of
wall of the MS in 100 hemifaces of human cadaveric heads the MS was evaluated in 150 patients (mean age 49.4 years)
using a transantral approach to the pterygopalatine fossa using CBCT by Kang et al. (2013). In 52.4 % the angle was
located immediately posterior to the maxillary sinus. The >60°, in 42.8 % 30–60°, and in 4.8 % <30°.
mean thickness of the posterior wall was 0.8 mm, but it var-
ied widely from 0.2 to 3.6 mm.
Ostium and Semilunar Hiatus
Fig. 9.35 Coronal CBCT image at the level of the missing left maxil-
lary first molar showing an unusually thick (>4 mm) lateral wall of the
maxillary sinus in a 48-year-old male
Ostium and Semilunar Hiatus 179
AN
CR
Root Positions Related to Maxillary Sinus age differences were observed. The most common vertical
positions of the first (77.5 %) and second molar (68.3 %) root
The position of the roots relative to the sinus floor has several apices were at the floor of the MS. Interestingly, a sinus
important clinical implications (Figs. 9.38 and 9.39). The expansion to the level of the bifurcation in first and second
most important aspect is the risk of exposure or tear of the molars was predominantly seen in younger subjects (10–
Schneiderian membrane during tooth extraction or surgical 19 years of age).
removal of teeth or roots (Fig. 9.40). Another concern is the Georgescu et al. (2012) assessed the bone dimensions
spread of periodontal and endodontic infection into the max- between root apices and sinus floor in 51 patients comparing
illary sinus and the risk of pushing medicaments or root panoramic radiography and CBCT. In contrast to the work
canal obturation materials through the apical foramina into by Sharan and Madjar (2006), no significant differences
the sinus cavity when performing endodontic treatment. were recorded between the two radiographic methods. Howe
Finally, roots positioned close to or protruding into the sinus (2009) assessed the concordance of CBCT and gross dissec-
cavity may result in sinus expansion into the posterior alveo- tion for dimensions of maxillary bone around 69 first molar
lar process with reduced bone height for eventual implant roots in 37 cadaveric specimens. The analysis revealed an
placement. Studies that have evaluated the distances between overestimation of 0.4 ± 1.1 mm for the CBCT measurement
the root apices and the floor of the MS are summarized in compared to gross dissection. The author concluded that
Table 9.2. Studies comparing the distances of all posterior CBCT measurements were acceptable for clinical accuracy.
teeth usually show that the first molar is the tooth closest Pagin et al. (2013) assessed in CBCT scans of 50 patients
located to the floor of the MS. The shortest mean distance (mean age 44.5 ± 15.1 years) whether the roots of posterior
(0.83 ± 0.49 mm), however, was recorded for the mesiobuc- maxillary teeth were in close contact with or protruded into
cal root of the second molar (Eberhardt et al. 1992). the sinus floor. A total of 601 roots in 315 teeth were evalu-
Sharan and Madjar (2006) compared paired panoramic ated. 21.6 % of roots were in contact with and 14.3 % pro-
radiographs and CT scans of 80 subjects regarding concor- truded into the floor. Marked differences were observed for
dance of root position relative to the sinus floor. Only 39 % the teeth. None of the first premolars and only 0.9 % of sec-
of the roots that were observed projecting into the sinus cav- ond premolars protruded into the sinus, whereas 12.9 % of
ity in panoramic radiographs also showed protrusion into the mesiobuccal roots of second molars did so. The latter finding
sinus with CT. The mean root projection length in the pan- confirms the close relationship of the mesiobuccal root of the
oramic radiographs was 3.1 ± 2.54 mm compared to only second molar and the floor of the MS as mentioned above.
1.5 ± 1.50 mm in CT scans, constituting a 2.1 factor differ- The findings that first (0–7.2 %) and second (2.5–13.6 %)
ence between the two visualization methodologies that was premolar roots only seldom protruded into the sinus cavity
also statistically significant. were corroborated by (von Arx et al. 2014a). The CBCT
Ariji et al. (2006) characterized the horizontal root posi- study comprised 177 first and 119 second premolars in 192
tions of maxillary molars relative to the buccal and palatal patients (mean age 58.4 ± 20.5 years). Ok et al. (2014) eval-
bone plates as well as the vertical root positions with respect uated CBCT scans of 849 patients. Instead of measuring
to the MS. Although measurements were not recorded, the the distance between the root tips of the posterior teeth and
spatial relationship between roots and frequencies of specific the floor of the maxillary sinus, they classified the interre-
patterns was evaluated utilizing axial CT scans of 120 lationship into three groups: type 1 with roots penetrating
patients. The most frequent pattern for first molars (62.9 %) the sinus floor, type 2 with roots contacting the sinus floor,
showed buccal roots contacting the buccal cortex and palatal and type 3 with roots positioned below the sinus floor. Type
roots contacting the palatal cortex, while the roots of second 1 prevailed in palatal roots of first molars, type 2 in mesio-
molars were most frequently located internal to the alveolar buccal roots of second molars, and type 3 in first and sec-
process and away from the cortices (63.8 %). No gender or ond premolars.
Root Positions Related to Maxillary Sinus 181
mb
db
pal
P
M3
M2
M1
Fig. 9.40 Perforation of the Schneiderian membrane of the maxillary
sinus during extraction of a first maxillary molar in a 63-year-old male
resulting in an oroantral communication. P site of perforation, mb
mesiobuccal socket, db distobuccal socket, pal palatal socket
Fig. 9.38 Sagittal CBCT image showing severely impacted second
and third maxillary molars in a 27-year-old male. M1 first molar, M2
second molar, M3 third molar
Fig. 9.39 The axial CBCT view demonstrates the location of the root
apices within the maxillary sinus
Table 9.2 Distances (mm) between root apices and maxillary sinus
182
Author(s) Study material N 1st premolar 2nd premolar 1st molar 2nd molar 3rd molar Comments
Eberhardt et al. 38 patients (CT) (age NA Buccal root: 2.86 ± 0.60 Mesiobuccal root: Mesiobuccal root: – –
(1992) NA) 6.18 ± 1.60 2.82 ± 0.59 0.83 ± 0.49
Palatal root: Distobuccal root: Distobuccal root:
7.05 ± 1.92 2.79 ± 1.13 1.97 ± 1.21
Palatal root: Palatal root:
1.56 ± 0.77 2.04 ± 1.19
Howe (2009) 37 cadaveric human 69 first molars – – Mesiobuccal root: – – Measurements were
maxillae (dissection Dissection: taken in coronal planes
and CBCT) (age NA) 1.3 ± 2.5
CBCT:
2.5 ± 3.4
Distobuccal root:
Dissection:
1.2 ± 1.6
CBCT:
1.8 ± 2.2
Palatal root:
Dissection:
0.9 ± 2.0
CBCT:
1.2 ± 2.2
+
Georgescu et al. 51 patients (CBCT and 61 1st premolars+, Panoramic Panoramic Mesiobuccal root: Mesiobuccal root: – Only premolars with
(2012) panoramic 62 2nd radiography: radiography: Panoramic Panoramic radiography: fused roots were
radiography) (mean age premolars+, 6.77 ± 3.94 4.98 ± 3.28 radiography: 3.37 ± 2.24 (0.5–11.3) assessed
48 ± 14 years, range 48 1st molars, (1.1–16.2) (0.5–15.9) 3.12 ± 2.34 *CBCT: *Measurements were
20–77 years) 66 2nd molars *CBCT: *CBCT: (0.3–13.6) 2.76 ± 2.35 (0.3–11.1) taken on sagittal
7.56 ± 3.96 4.64 ± 3.00 *CBCT: Distobuccal root: CBCT images
(0.4–14.6) (0.1–13.3) 3.02 ± 2.33 Panoramic radiography:
(0.3–10.5) 3.67 ± 2.24 (0.2–11.9)
Distobuccal root: *CBCT:
Panoramic 3.05 ± 2.21 (0.6–10.7)
radiography: Palatal root:
3.42 ± 2.32 Panoramic radiography:
(0.3–10.1) 3.18 ± 1.49 (0.8–6)
*CBCT: *CBCT:
3.0 ± 2.35 3.22 ± 2.24 (0.3–10.4)
(0.7–10)
Palatal root:
Panoramic
radiography:
9
2.56 ± 1.00
(0.5–4.6)
*CBCT:
3.08 ± 2.08
(0.3–9.8)
Maxillary Sinus
1
von Arx et al. 192 patients (CBCT) 177 first and 119 Buccal root: Buccal root: – – – Sagittal plane
1 2
(2014a) (mean age second premolars 15.15 ± 2.99 2.32 ± 2.19 Coronal plane
2 2 3
58.4 ± 20.5 years, range 8.28 ± 6.27 3.28 ± 3.17 Axial plane
3 3
19–81 years) 5.86 ± 3.54 2.40 ± 2.71
Palatal root: Palatal root:
1 1
4.20 ± 3.69 2.68 ± 3.58
2 2
7.17 ± 6.14 3.69 ± 4.51
3 3
5.71 ± 3.89 3.80 ± 3.71
Kang et al. (2015) 132 patients (CBCT) 264 teeth per Single-rooted: Single-rooted: Mesiobuccal root: Mesiobuccal root: – –
(mean age group 7.72 2.51 1.04 0.18
31 ± 9.0 years, range Buccal root: Buccal root: Distobuccal root: Distobuccal root:
21–59 years) 7.09 0.68 1.05 0.69
Palatal root: Palatal root: Palatal root: Palatal root:
6.13 0.88 1.04 1.61
Root Positions Related to Maxillary Sinus
183
184 9 Maxillary Sinus
Fig. 9.44 The intraoperative view clearly depicts the two prominent
septa (arrows) following osteotomy (lateral window approach)
Fig. 9.42 A sagittal CBCT image shows two pointed septa (arrows)
with intervening extremely thin bone (arrowhead) in a 48-year-old
male scheduled for sinus floor elevation in the edentulous segment of
his left maxilla
1
2 3
Canine root
Fig. 9.43 The axial CBCT image demonstrates the transverse (medio-
lateral) course of the septa forming three compartments within the
lower portion of the maxillary sinus
188 9 Maxillary Sinus
MSzr
Clinical Relevance of the Maxillary Sinus The MS has gained increasing interest following the
introduction of sinus floor elevation procedures in implant
In clinical dentistry, the MS must be carefully considered in surgery during the late 1970s by Tatum (Boyne and James
three primary fields including exodontia, endodontics, and 1980; Tatum 1986). Several methods of augmentation
implantology. Tooth extraction remains one of the most fre- involving the creation of a subantral space have since
quent dental procedures. Perforation of the Schneiderian mem- evolved using either a lateral approach (window tech-
brane during tooth extraction, and more rarely after tooth nique) or a crestal approach (osteotome technique) with a
extraction, remains a primary concern in the posterior maxilla, wide variety of modifications. The volume of bone or
albeit with relatively low risk. Punwutikorn et al. (1994) evalu- bone substitute needed for grafting the maxillary sinus
ated 27,984 extractions of posterior maxillary teeth with regard floor may be calculated using three-dimensional recon-
to sinus perforation. The overall perforation rate was 0.3 % struction of CT or CBCT images (Uchida et al. 1998b).
with first molar extraction showing the highest rate (0.64 %). Due to the complex anatomy of the floor of the MS, the
Most frequently, the sockets of the palatal roots were involved. pneumatization of the alveolar process, and the presence
Hirata et al. (2001) reported a rate of membrane perforation of of septa and vascular canals, cross-sectional imaging
3.8 % in 2038 tooth extractions, mostly for first molars. offers improved diagnostic efficacy and it is the preferred
With regard to third molars, Rothamel et al. (2007) method of preoperative assessment for sinus augmenta-
reported a perforation rate of 5 % during extraction of fully tion surgery (Harris et al. 2012). Three-dimensional radi-
erupted third molars, 10 % in surgical removal of partially ography also allows an assessment of sinus pathology
impacted third molars, and 24 % in surgical removal of fully facilitating alternative treatment options. Recently, a clas-
impacted third molars. These differences were all statisti- sification system for the level of difficulty (easy, moder-
cally significant. Lim et al. (2012) reported a perforation rate ate, difficult) was presented to characterize the impact of
of 2.5 % for surgically removed impacted third molars, but antral septum morphology on treatment strategies during
none of the conventionally extracted third molars produced a sinus floor elevation (Wen et al. 2013). The presence of
perforation, even those in close proximity to the sinus. septa has also been associated with a certain risk of rup-
Similarly, del Rey-Santamaria et al. (2006) observed no per- turing the Schneiderian membrane during sinus floor ele-
foration following conventional extraction of third molars, vation procedures (Schwartz-Arad et al. 2004; Malkinson
while a perforation rate of 5.7 % was noted during surgical and Irinakis 2009; von Arx et al. 2014b).
removal of maxillary third molars. Many clinical reports have documented complications
Endodontic implications of the maxillary sinus include associated with dental implants and the MS. The most fre-
extension of periapical infections into the sinus, the introduc- quently reported complication is the inadvertent displace-
tion of endodontic instruments and materials beyond the apices ment of an implant into the sinus (Table 9.6) (Chiapasco
of teeth in close proximity to the sinus, and the risks and com- et al. 2009; Gonzalez et al. 2012). The dental implant may be
plications associated with endodontic surgery (Haumann et al. dislodged into the sinus when inserting the implant or when
2002). The MS poses a special challenge when root canal treat- connecting the abutment to the implant. However, many
ment is performed in teeth with roots in close proximity to or reports have described “migration” of a dental implant into
even protruding into the sinus. Although it is well established the maxillary sinus or adjoining areas (middle meatus, eth-
that all endodontic instruments and materials should be moid sinus, sphenoid sinus). The reasons given for “implant
restricted to the confines of the root canal system, procedural migration” are as follows: (I) negative changes of intraspinal
errors such as introduction of instruments and medicaments and nasal air pressure resulting in a suction effect, (II) peri-
beyond the apical foramen are common and part of everyday implant bone destruction causing de-osseointegration of the
practice (Haumann et al. 2002). A case with extensive extru- dental implant, and (III) incorrect distribution of occlusal
sion of gutta-percha into the MS has been recently published forces by prosthodontic implant suprastructures (Regev et al.
(Brooks and Kleinman 2013). A perforation rate of 9.6 % was 1995; Galindo et al. 2005; Galindo-Moreno et al. 2012).
observed in a sample of premolar and molar apical surgeries, Other complications related to placement of dental implants
whereas others have reported a rate of oroantral communica- in the proximity of the MS or in conjunction with sinus floor
tion up to 50 % during apical surgery (Oberli et al. 2007). elevation procedures include severe sinus hemorrhage, max-
Anatomical variations of the MS, in particular alveolar recesses, illary sinusitis, and oroantral fistula (Regev et al. 1995;
may mimic periapical lesions or cysts (Sekerci et al. 2013). Hunter et al. 2009; Hong and Mun 2011).
194 9 Maxillary Sinus
Table 9.6 Overview of case reports with dislodgement of dental implants into maxillary sinus
Time elapsed
Patient (age/ since implant Signs,
Author(s) sex) Implant site Side placement Dislodgement symptoms Comments
Regev et al. 61/male Canine Right 2 months Migration N/A Patient expelled
(1995) another implant
placed near the
midline through the
nose upon sneezing
2 months after
implantation
66/female 2nd molar Left 6 months Displacement – Implant was dislodged
upon reentry and
abutment connection
Iida et al. (2000) 50/male 2nd molar Right 16 years Migration None 5 years after implant
placement, patient
noted mobility of
implant; prosthesis
was removed, but
implant was left in
place
Raghoebar and 56/male 2nd premolar Right 5 months Migration None –
Vissink (2003)
Nakamura et al. 44/male 2nd molar Left Immediate Displacement – –
(2004)
El Charkawi et al. 19/female 1st molar Left Immediate Displacement Acute sinusitis Implant was installed
(2005) immediately after
tooth extraction
Galindo et al. 42/male 2nd premolar Left 4 years Migration None –
(2005) 52/male 2nd molar Left 3 years Migration None –
Kim et al. (2007) 52/female 2nd molar Left 18 months Displacement Acute sinusitis Dentist tried to
remove the implant
(suspected to cause
sinusitis) when he
displaced the implant
into the sinus
Kitamura (2007) 54/female 2nd molar Right >3 years Migration Acute sinusitis –
Felisati et al. 45/female 1st molar Left Immediate Displacement None Two weeks later,
(2007) implant had migrated
spontaneously to the
sphenoethmoid recess
Chappuis et al. 59/female 2nd premolar Right Immediate Displacement – Private dentist
(2009) performed staged
sinus floor elevation
9 months earlier;
during second stage
surgery using the
osteotome technique,
the implant
disappeared into the
sinus
Chiapasco et al. 13 males and 14 NA 12 right NA NA 13 maxillary Publication with
(2009) females 15 left sinusitis largest number of
(mean age cases (n = 27)
53.9 years, regarding implants
range displaced into
27–73 years) maxillary sinus
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Hard and Soft Palate
10
The palate comprises the hard and the soft palate gitudinal soft tissue band, called the palatine raphe, is found
simultaneously forming the roof of the oral cavity and the in the midline extending to the incisive papilla. The latter
floor of the nasal cavity (Figs. 10.1 and 10.2). The U-shaped overlies the incisive foramen (Chap. 7).
dental arch provides the anterior and lateral border of the The soft palate comprises a horizontal aponeurosis and sev-
hard palate, while the free margin of the soft palate repre- eral muscles that are also discussed later in this chapter. The
sents the posterior border of the palate. The internal struc- soft palate is highly mobile and acts as a valve separating the
tures of the hard palate include the palatine processes of the nasopharynx from the oropharynx during deglutition, thus
os maxilla (anterior three quarters) and the horizontal plates preventing backflow of food and liquid into the nasal cavities.
of the os palatinum (posterior quarter). The midline suture is The uvula is a highly visible primary structure of the soft pal-
termed the median palatine suture. Posteriorly the palatine ate located along the midline and distal end of the soft palate.
processes of the os maxilla articulate with the horizontal The arterial supply of the hard palate is from the greater
plates of the palatine bone at the palatomaxillary suture palatine artery originating from the descending palatine
(Fig. 10.3). Prominent landmarks of the hard palate comprise artery and the nasopalatine artery originating from the sphe-
the palatal opening of the nasopalatine canal, i.e., the incisive nopalatine artery. In LeFort I osteotomy, there is a certain
foramen (Chap. 7), and the greater and lesser palatine foram- though low risk of severing or tearing the descending pala-
ina that are addressed in this chapter. The bony surface of the tine artery. There may be additional supply from the arteries
hard palate is pitted with numerous foramina for nutrient of the soft palate, i.e., the ascending palatine artery and the
vessels and depressions for the lodgment of the palatine branches from the ascending pharyngeal artery (Gauthier
glands (du Toit and Nortjé 2003). The hard palate is covered et al. 2002). Innervation to the palate is provided by the naso-
with masticatory mucosa that displays in the anterior region palatine nerve (Chap. 7) and the greater and lesser palatine
transverse folds, the so-called rugae. A slightly elevated lon- nerves that are discussed in this chapter.
Hard
palate
Soft
palate
IF
MidC
MPS
IC
IC OMp OMp
PMS
OMa
OPh
GPF GPF
OPh OPh
OMp
Hard palate
Soft palate Hard palate NVB LPF LPF
M1
Fig. 10.3 Inferior view of hard palate in an adult human dry skull.
GPF greater palatine foramen, IF incisive foramen, LPF lesser palatine
Fig. 10.2 Dissection of a left cadaveric hemiface viewed from the foramen, MPS median palatine suture, OMp palatal process of os max-
medial perspective showing hard and soft palate. IC inferior concha, illa, OPh horizontal plate of os palatinum, PMS palatomaxillary suture
OMa alveolar process of os maxilla, OMp palatal process of os maxilla,
OPh horizontal plate of os palatinum, M1 first molar, MidC middle con-
cha, NVB neurovascular bundle (greater palatine artery and nerve)
Vault of the Hard Palate 201
Vault of the Hard Palate associated with a highly resorbed and atrophic maxilla.
Saralaya and Nayak (2007) studied the shape of the palatal
The cross section (coronal plane) of the palate demon- vault in 132 Indian adult dry skulls. The vault was arched
strates the shape of the palatine vault. The shape is either (46.2 %), flat (37.1 %), or highly arched (16.7 %). The
flat, arched (inverted U-shape), or pointed (inverted height of the vault has been analyzed in only few cadaver
V-shape). While edentulous maxillae may show all three studies (Table 10.1). Reported means of palate height
types of vault, dentate maxillae are usually not flat but ranged from 13.2 to 18.5 mm, depending on site and gen-
curved due to the presence of teeth with the prominent der. Males appear to have higher palatal vaults than females
alveolar process. In contrast, a flat palate is typically (Klosek and Rungruang 2009; Kim et al. 2014).
Length, Width, and Thickness of the Hard Paramedian bone heights were generally higher than median
Palate bone heights at 3 and 6 mm posterior to the incisive foramen
but were similar at 9- and 12-mm levels.
Studies evaluating the length and width of the hard palate in Gracco et al. (2008) used CBCT images to quantify the
dry skulls or cadaveric heads are summarized in Table 10.1. palatal bone thickness in 162 subjects (age range 10–44
The mean length in adults ranged between 39.6 and 53.1 mm, years). Ninety-degree paracoronal views of the palatal region
and the mean width in the molar area between 31.1 and at 4, 8, 16, and 24 mm posterior to the incisive foramen were
43.5 mm. Knowledge of the thickness of the hard palate is reconstructed, and bone height was measured at the midline
important for the placement of palatal implants that are used and at 3 and 6 mm lateral to the midline. The bone height in
for orthodontic treatment of dental and skeletal dysgnathia the midline averaged between 3.9 mm (posterior sites) and
(Fig. 10.4). Hence, the assessment of the sites with maxi- 9.0 mm (anterior sites), between 2.7 and 8.7 mm at 3 mm
mum bone volume available for implant placement is of lateral to the midline, and between 2.3 and 10.4 mm at 6 mm
great interest. Several cadaver and radiologic studies have lateral to the midline.
investigated the thickness of the palatine bone. Gahleitner Identical locations for measuring the palatal bone thickness
et al. (2004) reconstructed paracoronal CT scans to measure were used by Marquezan et al. (2012) in 36 patients (mean age
the palatal bone height in 3 mm increments dorsally to the 23.6 ± 11.9 years). Paracoronal CBCT images were analyzed.
incisive foramen in 32 patients (mean age 26 years, range The bone height in the midline averaged between 5.1 mm
12–49 years). The overall mean palatal bone height for all (posterior sites) and 7.6 mm (anterior sites), between 2.1 and
patients, planes, and regions was 5.01 ± 2.60 mm, ranging 6.9 mm at 3 mm lateral to the midline, and between 1.5 and
from 0 to 16.9 mm. The mean available bone height for a 7.3 mm at 6 mm lateral to the midline. The thickness of the
single site was found to be best at 6 mm posterior to the inci- cortical plate in all evaluated sites lateral to the midline ranged
sive foramen with a mean height of 6.17 ± 2.81 mm. between 1.12 and 1.9 mm.
Posterior Nasal Spine nasal spine did not show significant variations in shape or
size that contribute to the length of the palate. Some
The posterior nasal spine is a bony protuberance at the notching or flattening of the posterior nasal spine was
posterior border of the hard palate made up of bilateral observed in skulls without teeth and with resorption of the
and fused bony spiculae of the horizontal plates of the alveolar process and was related to the general flattening
palatine bone (Fig. 10.5). In a study of 68 Caucasian and thinning of the palate in such cases (Krmpotic-
skulls (age range 2 months to 90 years), the posterior Nemanic et al. 2008).
The Pterygopalatine Canal (Palatine Canal) Anatomical and radiographic studies have documented
the length and angle of the pterygopalatine canal
The anatomy of the pterygopalatine canal is of interest to den- (Table 10.2). Some studies have measured the length of the
tists, oral maxillofacial surgeons, and otolaryngologists per- GPC while others have included the length of the pterygo-
forming procedures in this area, e.g., administration of local palatine fossa above the canal, explaining the marked dif-
anesthesia, dental implant placement, orthognathic LeFort I ferences of the given mean measurements (10–32.5 mm).
osteotomies, and sinonasal surgeries (Meechan et al. 2000; More consistent are the data regarding the mean angle
Broering et al. 2009; Howard-Swirzinski et al. 2010). The between the GPC and the horizontal palate (57.9°–67.4°).
pterygopalatine canal initiates in the pterygopalatine fossa Methathrathip et al. (2005) evaluated in 105 Thai adult dry
(Chap. 12) and descends through the maxilla typically divid- skulls the frequency of the anatomical obstruction in
ing into greater palatine canals (GPC) and lesser palatine attempting to reach the foramen rotundum with a needle
canals (LPC) transmitting the arteries and nerves of the same inserted inferiorly into the GPC and ascending to the pter-
name (Figs. 10.6, 10.7, 10.8, 10.9, 10.10, and 10.11). The ygopalatine fossa. In 47.6 %, the needles were obstructed
pterygopalatine fossa commonly is infiltrated to reduce bleed- before reaching the foramen rotundum, mostly at the ante-
ing during paranasal sinus surgery. Knowledge of the length of rior border of the lateral pterygoid plate. In 31.7 % the
the pterygopalatine canal is critical for proper placement of needle was pushed into the orbit and in 8.7 % into the
local anesthetic to achieve maximal effect while minimizing brain!
the likelihood of complications. Douglas and Wormald (2006) Regarding the positional relationship of the GPC to the
recommended the use of a 25-gauge needle with a bend at LeFort I osteotomy, Li et al. (1996) measured the distance
25 mm from the tip and angled at 45° to perform these injec- from the nasal aperture (piriform rim) to the GPC in 40
tions based on the width of the mucosa (approximately 7 mm) patients (mean age 41 years) using CT imaging. In females,
overlying the GPF and the length (approximately 18 mm) of the mean distance 3 mm above and parallel to the nasal floor
the GPC. This technique would ensure optimal penetration up was 34.6 mm (28–43 mm) and in males 38.4 mm (34–
to the pterygopalatine fossa with deposition of the local anes- 42 mm). The authors concluded that injury to the descending
thetic into the fossa and maximal vasospasm of the maxillary palatine artery could be minimized by limiting the osteotomy
artery with a minimal risk to the orbital contents, infraorbital to 30 mm in females and to 35 mm in males posterior to the
nerve, and maxillary artery (Douglas and Wormald 2006). piriform rim.
The Pterygopalatine Canal (Palatine Canal) 205
Sphenoid sinus
Sphenoid
PPF sinus
Maxillary PPF
sinus
MidC
PPC
PPC
IC
LPC GPC
GPC
PTPlp
M3
GPF
GPF
LPF
M2
Fig. 10.6 Sagittal CBCT image showing greater and lesser palatine
canals in a 20-year-old female. GPC greater palatine canal, GPF greater
palatine foramen, LPC lesser palatine canal, LPF lesser palatine fora-
men, PPC pterygopalatine canal, PPF pterygopalatine fossa, PTPlp
lateral plate of pterygoid process
206 10 Hard and Soft Palate
IOC
MidC
Maxillary sinus
MS
GPC IC GPC
GPF
MT
LPC
Fig. 10.8 Sagittal CBCT image showing greater and lesser palatine Fig. 10.9 Coronal CBCT image showing greater palatine canal and
canals in a 42-year-old male. GPC greater palatine canal, IOC infraor- foramen. GPC greater palatine canal, GPF greater palatine foramen, IC
bital canal, LPC lesser palatine canal inferior concha, MidC middle concha, MS maxillary sinus, MT maxil-
lary tuberosity
LPC
Maxillary
IC
sinus
GPC
LPF
MT
LPC
Fig. 10.11 Axial CBCT image showing greater and lesser palatine
canals. C canine root, GPC greater palatine canal, IC inferior concha,
LPC lesser palatine canal
Fig. 10.10 Coronal CBCT image showing lesser palatine canal and
foramen. LPC lesser palatine canal, LPF lesser palatine foramen, MT
maxillary tuberosity
The Pterygopalatine Canal (Palatine Canal) 207
Table 10.2 Length (mm) and angulation (°) of the greater palatine canal (GPC)
Angle of GPC Angle of GPC
Length of relative to relative to
Author (s) Study material N GPC palate pterygopalatine fossa Comments
Li et al. (1996) 30 adult dry skulls 60 10 (6–15) – – Length of GPC above
nasal floor
Cheung et al. (1998) 30 Chinese adult dry 60 – 60.8 ± 7.27 – –
skulls (CT) (51.1–71)
Methathrathip et al. 105 Thai adult dry skulls 206 *29.7 ± 4.2 57.9 ± 5.8 Angle relative to *Length of GPC and
(2005) (16.3–40.9) (40–78) vertical plane: pterygopalatine fossa
6.7 ± 5.2 (0–25.8)
Douglas and Wormald 21 cadaveric heads (CT) 42 18.5 (95 % CI: – – Measured on
(2006) 17.9–19.1) parasagittal CT scans as
the distance from the
GPF to the point where
the canal flared to form
the pterygopalatine
fossa
Howard-Swirzinski 500 patients (CBCT) 1000 29 ± 3.0 – – Length measured from
et al. (2010) (age range 18–73 years) (22–40) the center point of the
pterygopalatine fossa
(pterygoid canal)
Hwang et al. (2011) 50 patients (CT: 3D 100 13.8 ± 2.0 67.4 ± 6.9 159.8 ± 7.1 –
reconstructions) (mean
age 51 years, range
19–84 years)
Sheikhi et al. (2013) 138 patients (CBCT) 276 All: 31.8 ± 1.37 – – Length measured from
(age range 18–77 years) Males: the center point of the
1
32.5 ± 2.37 pterygopalatine fossa
Females: (pterygoid canal).
2 1,2
30.6 ± 1.76 Significant difference
1,2
Rapado-Gonzalez et al. 150 patients (CBCT) NA Males: – – Significant difference
1
(2015) (age NA) 12.9 ± 1.7
Females:
2
12.0 ± 2.02
208 10 Hard and Soft Palate
Greater Palatine Foramina: Location on the midline to the posterior nasal spine, in fact, did not
change significantly with age, even in a group of subjects
The inferior opening of the GPC is the greater palatine fora- aged between 8 and 16 years undergoing extensive growth.
men (GPF) located far back in the hard palate at the junction Other references to locate the GPF include the midline of
of the horizontal and vertical parts of the palatine bone the palate, the posterior border of the palatine bone, and the
(Fig. 10.12). Many studies have assessed the location of the incisive foramen (Table 10.4). A consistent mean distance
GPF relative to the adjacent teeth (Table 10.3). The majority (14.4–16.7 mm) between the GPF and the palatine midline
of investigations have located the GPF on the palatal aspect was documented in several anatomical and radiographic sur-
between the second and third molar or palatal to the third veys. Most studies also reported a high concordance between
molar. While the maxillary molars usually serve as reference left and right measurements underlining the symmetry of the
points to locate the GPF in dentate patients, they are not avail- horizontal GPF location. A posterior reference point for GPF
able for this purpose in edentulous patients. Hwang et al. position was assessed by Sharma and Garud (2013) who
(2011) suggested using the posterior nasal spine as a land- measured the distance from the GPF to the hamulus (mean
mark due to its consistent position. Kang et al. (2012) demon- 11.8 ± 2.23 mm). They suggested using the palpable hamulus
strated that the distance from a point with the GPF projected as a landmark for location of the GPF.
GPF GPF
PNS
Fig. 10.12 Inferior view of LPF LPF
posterior hard palate of dry skull
showing bilateral asymmetries of
the greater and lesser palatine Ham
foramina. GPF greater palatine PTPlp
PTPlp Ham
foramen, Ham hamulus of medial
pterygoid plate, LPF lesser
palatine foramen, PNS posterior
nasal spine, PTPlp lateral plate of
pterygoid process
Greater Palatine Foramina: Location 209
Table 10.3 Location of the greater palatine foramen (GPF) relative to the adjacent teeth
GPF
palatal GPF
GPF between GPF palatal GPF palatal palatal
palatal first and opposite between GPF palatal distal to
opposite second second second and opposite third
Author (s) Study material N first molar molar molar third molar third molar molar Comments
Ajmani (1994) 65 Nigerian dry 130 – – 13.1 % 78.5 % 8.5 % – Fully dentate
adult human maxillae with
skulls erupted third
34 Indian dry 68 – – – 54.4 % 42.6 % 2.9 % molars
adult human
skulls
Cheung et al. (1998) 20 Chinese 39 – – 48.7 % – 48.7 % 2.6 % Only skulls
adult dry skulls with third
molars
105 Thai adult 320
Methathrathip et al. – – 5.6 % 23.1 % 64.4 % 6.9 % –
(2005) dry skulls and
55 Thai
cadaveric heads
Saralaya and Nayak 132 Indian adult 264 – – 0.4 % 24.2 % 74.6 % 0.8 % All skulls
(2007) dry skulls with fully
erupted third
molars
Klosek and 41 Thai 17 females – 14.3 % 35.7 % 35.7 % 14.3 % – –
Rungruang (2009) cadaveric heads 24 males – – 65 % 10 % 25 % – –
(dissection)
age 51 years, range 19–84 Males: 4.6 ± 0.7 16.7 ± 1.3 *Females: All: 10.7 ± 1.8 *Distance from GPF to
2
years) Females: 4.4 ± 0.7 Females: 5.7 ± 1.6 Males: 11.0 ± 1.5 posterior nasal spine
2
Short axis: 15.8 ± 1.1 Females: 10.4 ± 1.9
All: 2.2 ± 0.4
Males: 12.4 ± 0.4
Females: 22.1 ± 0.4
Kang et al. (2012) 107 patients (CT with 3D 107 – – *5.53 ± 2.20 Distance from GPF to *Distance from GPF to
reconstruction) (mean age (0.9–11.6) occlusal plane: 22.1 ± 3.36 posterior nasal spine
35.8 ± 15.4 years) (13.4–30.7)
Piagkou et al. (2012) 71 Greek adult dry skulls 142 Anteroposterior: 5.3 ± 0.9 15.3 ± 1.3 4.6 ± 1.0 – –
Mediolateral: 2.6 ± 0.6
Ikuta et al. (2013) 50 Brazilian patients 100 *3.1 ± 0.47 *15.2 ± 1.45 – Horizontal distance from *Measured on axial and
(CBCT) (mean age medial border of GPF to coronal sections;
35.8 ± 11.0 years) alveolar ridge **Measured on axial
**7.9 ± 2.04 sections
Sharma and Garud 100 Indian dry adult 198 *4.72 ± 1.40 14.5 ± 1.79 **3.4 ± 1.47 Distance from GPF to *Anteroposterior
(2013) skulls incisive foramen: dimension;
35.5 ± 2.59 **Measured from the GPF
Distance from GPF to to the point of maximum
pterygoid hamulus: concavity of the posterior
11.8 ± 2.23 palatal border
211
212 10 Hard and Soft Palate
Greater Palatine Foramina: Shape ing a needle into the foramen. The direction of the opening
was anterior (69.4 %), anteromedial (18.8 %), or inferior
The shape of the GPF was found to be mostly elliptic (11.9 %). The sample utilized by Sharma and Garud (2013)
(90.2 %) and oriented anteroposteriorly (Klosek and as noted above displayed one skull that completely lacked
Rungruang 2009). In a separate study, the shape of the GPF the GPF bilaterally. The other 198 GPF mostly presented an
was mostly oval (82.4 %) and less frequently lancet-shaped anteromedially (49.5 %) or inferiorly (45.0 %) directed open-
(7.1 %), slit-shaped (5.7 %), or round (4.8 %) (Methathrathip ing. Less frequent were anteriorly (2 %) or anterolaterally
et al. 2005). A bony projection is occasionally observed (3.5 %) directed openings.
along the posterior margin of the GPF. This structure, called
the posterior palatine crest, is formed by a bony eminence of
the pyramidal process, and it may be confused with the tip of Lesser Palatine Foramina
the pterygoid hamulus when palpating the posterior palate in
the living subject. The posterior palatine crest may irritate The lesser palatine foramina (LPF) are located in the pyrami-
the overlying mucosa as a result from denture pressure as dal process of the palatine bone, thus posterior to the GPF
reported by Lee et al. (2001). These same authors reported a (Fig. 10.12). LPF are smaller than GPF but outnumber the
prevalence of 13.8 % for the posterior palatine crest in 160 GPF. Saralaya and Nayak (2007) studied the number of LPF
Korean adult dry skulls. In a study of 71 Greek adult dry in 132 Indian adult dry skulls. The number of LPF varied
skulls, a high eminence behind the GPF was observed in from one to four and the mean number of LPF per side was
33.8 % of cases (Piagkou et al. 2012). In 27.8 % of 100 Indian 1.8 ± 0.66. In general, the number of LPF was not symmetri-
dry adult skulls, a bony projection from the posterior border cal. In two skulls, the LPF were absent on the left side.
of the GPF was observed (Sharma and Garud 2013). Piagkou et al. (2012) assessed the LPF in 71 Greek adult dry
skulls. A total of 240 LPF were identified with the following
frequencies: 53.5 %, one LPF was present per side; 31 %,
Greater Palatine Foramina: Direction two LPF; 10.6 %, three LPF; 2.8 %, four LPF; and 2.1 %, five
LPF. The foramina were located at a mean distance of
The GPF is usually directed inferiorly in an anteromedial 14.6 ± 2.2 mm from the midline. The LPF were either located
direction. However, other directions have been described within the palatine bone (right side 20.2 %, left side 11.5 %),
explaining the difficulty of introducing an injection needle at the junction of the palatine bone and the pterygoid process
into the GPF and into the pterygopalatine canal (Ajmani (right side 67.7 %, left side 76.1 %), or within the pterygoid
1994). Additional studies on dry skulls have evaluated the process (right side 12.1 %, left side 12.3 %). A communica-
direction of the opening of the GPF. In 132 Indian adult dry tion between the lesser and greater palatine foramina was
skulls, the opening was found in 46.2 % to be oriented observed in 21.3 % on the right side and in 22.5 % on the left
anteromedially, whereas in 41.3 % it was directed anteriorly side. Sharma and Garud (2013) reported a mean number of
and in 12.5 % anterolaterally. In one skull, the GPF was LPF in 100 dry adult Indian skulls as 1.39 and 1.45 for the
duplicated on one side (Saralaya and Nayak 2007). In a study right and left sides, respectively (range 0–5). Bilateral
of 100 Brazilian adult dry skulls, Chrcanovic and Custodio absence of the LPF was seen in two skulls, while unilateral
(2010) analyzed the direction of the GPF’s opening by insert- absence was noted in 12 skulls.
Sulcus Palatinus 213
Sulcus Palatinus measured the distance from the alveolar crest to the sulcus
palatinus along the bony palatal slope. At the site of the first
The sulcus palatinus is a groove-like structure extending from premolar, the distance measured on average 5.7 ± 2.2 mm and
the GPF anteriorly (Figs. 10.13, 10.14, 10.15, 10.16, and at the second molar site 7.9 ± 2.1 mm. No significant differ-
10.17). The sulcus is usually located at the junction of the ences were found comparing distances in males and females.
alveolar process and the horizontal plate of the palate. The Yu et al. (2014) assessed the morphology of the palatal
neurovascular bundle comprising branches of the greater pala- spine in cadaveric hemifaces and dry skulls. The spine was
tine artery courses anteriorly through the sulcus palatinus. on average located 6.5 ± 1.76 mm anterior to the margin of
However, these structures typically are not visible radiograph- the greater palatine foramen in the second molar area, with a
ically. Damage to the greater palatine artery and nerve is mean length of 10.4 ± 2.45 mm, mostly disappearing in the
avoided by appreciating the distance between the bony crest first molar area. Most commonly the spine presented a sharp
and the sulcus. The sulcus may also be separated in two or edge (66.3 %) thereby dividing the palatal groove through
multiple grooves by linear bony prominences, also called pala- which the palatal neurovascular bundle passes within a
tine ridges (Lee et al. 2001). Those authors reported a preva- medial and a lateral portion of the groove. In 19.8 %, the
lence of 33.8 % of palatal ridges, mostly observed in the grooves were covered with bony or fibrous ligaments. In
posterior half of the hard palate. Klosuk and Rungruang (2009) 13.9 %, a palatal spine was indistinct.
PR
PR PS
PS
PS
PS
GPF GPF
LPF LPF
C C
NPC
Maxillary Maxillary
sinus sinus
PS
PS
PS PS
uvula
Sulcus Palatinus 215
IC Maxillary
sinus
NPC C
PS
PR
Maxillary
sinus
PS pM1
PR
Fig. 10.16 Coronal CBCT image of left palate exhibiting a palatine
ridge and sulcus. IC inferior concha, PR palatine ridge, PS palatine
PS
mbM2 sulcus
dbM2
pM 2
Maxillary
sinus
Fig. 10.15 Axial CBCT image of left palate demonstrating the pala-
tine ridge and sulcus in a 52-year-old male. C root of canine, NPC naso-
palatine canal, pM1 palatal root of first molar, mbM2 mesiobuccal root
of second molar, dbM2 distobuccal root of second molar, pM2 palatal
root of second molar, PR palatine ridge, PS palatine sulcus
IC
IC
Maxillary
sinus Maxillary
PS sinus
PS
PR
PR
Greater Palatine Artery (canine to first molar area). The authors measured the dis-
tance from the alveolar crest to the GPA as well as the depth
The greater palatine artery (GPA) originates from the of the artery in relation to the mucosal surface. The mean
descending palatine artery branching from the maxillary measurements for the distance at the canine, first and second
artery within the pterygopalatine fossa (Chap. 12). The premolar, and first molar sites were 7.8 ± 2.43 mm,
descending palatine artery enters and courses through the 9.2 ± 2.55 mm, 10.9 ± 2.17 mm, and 11.3 ± 1.11 mm, respec-
pterygopalatine canal to emerge from its inferior opening, tively. The overall mean distance was 10.3 ± 2.29 mm. The
the GPF, where it terminates as the greater palatine artery values for the mean depth of the artery at the same tooth
(Figs. 10.18, 10.19, and 10.20). From the foramen, the GPA levels were 4.0 ± 0.57 mm, 3.1 ± 0.84 mm, 3.6 ± 1.08 mm,
courses anteriorly through the sulcus palatinus. The GPA and 5.5 ± 2.72 mm, respectively. The overall mean depth of
eventually reaches the incisive foramen where it forms anas- the GPA was 4.3 ± 2.07 mm.
tomotic connections with the nasopalatine artery (Chap. 7). Kim et al. (2014) assessed the location of the GPA relative
The mean width of the GPA was measured at three locations to the gingival margin, to the CEJ of the adjacent teeth, and
following dissection of 41 Thai cadaveric heads revealing to the surface of the palatal masticatory mucosa in 43 decal-
that the mean width of the artery was 2.65 ± 1.3 mm at the cified and hemisectioned cadaveric heads. The mean
GPF, 1.96 ± 0.9 mm at the level of the first premolar, and diameter of the GPA ranged from 1.3 ± 0.4 mm (first molar
1.1 ± 0.5 mm at the incisive foramen (Klosek and Rungruang site) to 0.8 ± 0.4 mm (canine site). The mean distance from
2009). These authors also described a frequent branching of the GPA to the gingival margin varied from 10.7 ± 3.0 mm
the artery on each level along its course; however, most (canine site) to 14.6 ± 2.2 mm (second premolar site). The
branches arose on the lateral side toward the alveolar process mean distance between the GPA and the CEJ ranged from
(65.6 % in females and 80.6 % in males). 10.6 ± 2.9 mm (canine site) to 14.0 ± 2.1 mm (second
The mean distance between the neurovascular bundle and premolar site). The depth of the GPA relative to the closest
the CEJ assessed in 11 cadaveric maxillae was 13.1 ± 2.0 mm mucosal surface varied from 2.3 ± 1.0 mm (canine site) to
at the level of the first molar and 12.2 ± 2.0 mm at the level of 5.7 ± 2.2 mm (second molar site).
the first premolar (Fu et al. 2011). In a similar study evaluat- Yu et al. (2014) classified the branching pattern of the
ing 16 dentate hemimaxillae, the GPA was located GPA into four types according to the location of the origins
11.9 ± 1.8 mm below the CEJ at the mesial line angle of the of the medial and canine arterial branches in 36 hemimaxil-
first molar (Benninger et al. 2012). This value corresponded lae of embalmed Korean cadavers. In type I, which was the
to a level of 76 % (range 68.5–87.5 %) of the palatal height. most prevalent (41.7 %, n = 15), the lateral branch ran anteri-
Therefore, the most apical horizontal incision should be posi- orly in the lateral groove of the bony prominence from the
tioned at no more than 68.5 % of the palatal height from the greater palatine foramen and gave off a medial and a canine
CEJ for adequate protection of the neurovascular bundle dur- branch distal to the bony prominence. In type II (33.3 %,
ing harvesting of a palatal mucosal or connective tissue graft. n = 12), the medial branch arose from the lateral branch
In every dissection, the authors documented a visible and pal- before reaching the bony prominence and ran in the medial
pable crest separating bony grooves and that the GPA was groove of the bony prominence. In type III (16.7 %, n = 6),
positioned within the lateral groove while the nerve traversed the lateral branch gave off a canine branch immediately after
the medial groove. The structure appeared to be confined to passing through the GPF. Finally, in type IV (8.3 %, n = 3),
the palatine process of the maxillary bone, and the authors the medial branch arose from the lateral branch before it
suggested that structure be formally termed the “greater pala- reached the bony prominence and ran together with the lat-
tine crest of the maxillary bone” (Benninger et al. 2012). eral branch in the lateral groove of the bony prominence. The
Others have named the same structure palatine ridge (Lee same authors also reported the following mean distance from
et al. 2001) (see section on sulcus palatinus above). the GPA to the CEJ of the adjacent teeth: 9.0 mm (canine),
Cho et al. (2013b) assessed the location of the GPA in 11.1 mm (first premolar), 13.5 mm (second premolar),
histologic specimens obtained from 16 cadaveric maxillae 13.8 mm (first molar), and 13.9 mm (second molar).
Greater Palatine Artery 217
MN
MO
DPA
LPN
LPA
GPN/A
M2
Fig. 10.18 Dissection of the right side of a cadaveric head with the Fig. 10.19 Dissection of the left palate showing the tortuous route of
maxillary sinus exposed showing the descending palatine artery, the the greater palatine artery (dotted lines)
greater and lesser palatine arteries as well as the accompanying nerves
(anterolateral and posterior bone walls of maxillary sinus have been
removed as well as part of the zygomatic bone/arch). DPA descending
palatine artery, GPN/A greater palatine nerve and artery, LPA lesser
palatine artery, LPN lesser palatine nerve, M2 second molar, MN trunk
of maxillary nerve (held laterally with instrument, not shown), MO
maxillary ostium
218 10 Hard and Soft Palate
PR
PS
GPF
The greater palatine nerve (GPN) originates from the maxil- The lesser palatine nerve (LPN) is variable in its origin but
lary nerve (second division of CN V) within the pterygopala- typically forms in conjunction with the GPN. However, the
tine fossa (Chap. 12) and courses together with the GPA LPN usually courses in a separate canal arising at the inferior
through the pterygopalatine canal and greater palatine canal, portion of the pterygopalatine canal to exit from the lesser
respectively (Figs. 10.18, 10.19, and 10.20). After exiting the palatine foramina (see above). The LPN innervates the
foramen, the GPN courses anteriorly supplying the palatal mucosa of the soft palate including minor salivary glands of
masticatory mucosa. This nerve carries sensory fibers as well that region. In addition, some authors observed that motoric
as parasympathetic fibers to the minor salivary glands of the fibers traveling with the LPN innervate the uvular muscle
palate. There is still controversy concerning the anterior exten- and co-innervate the tensor veli palatini and the palatopha-
sion of the GPN innervation of the palate with some authors ryngeus (Shimokawa et al. 2005).
believing that the GPN innervation does not reach the area
beyond the first premolar, while others claim an extension up
to the incisive foramen, or even an anastomosing pattern of the
terminal branches of the GPN and of the nasopalatine nerve
(Chap. 7) (Langford 1989; Filippi et al. 1999).
Palatal Mucosa 219
Palatal Mucosa Buff et al. (2011) evaluated sensitivity changes of the pala-
tal mucosa in 14 patients after harvesting mucosal grafts from
The palatal aspect of the posterior maxillary process is a the right side of the palate. Minimal two-point discrimination
major donor site for harvesting full mucosal or connective measured at 5 mm from the gingival margin in canine sites
tissue grafts (Figs. 10.21, 10.22, 10.23, and 10.24). The was statistically greater in donor sides (6.6 ± 3.79 mm) com-
latter are mainly used in periodontology and dental pared to contralateral nondonor sides (4.7 ± 4.14 mm). The
implantology for increasing the dimensions of keratinized authors concluded that sensory changes might occur after soft
mucosa around teeth and implants, for covering exposed tissue harvesting from the palate.
roots, and for increasing localized alveolar ridge Several methods of mucosa thickness assessment have been
thickness. However, the proximity of the neurovascular described and documented in the literature. These include inva-
bundle running anteriorly from the GPF must be consid- sive measurement using needles, endodontic instruments
ered as well as the thickness (depth) of the palatal mucosa (reamers) or periodontal probes, noninvasive measurement
(PMC). applying ultrasonic or CT/CBCT imaging (Table 10.5).
Fig. 10.22 The palatal mucosal grafts were used to optimize the kera-
tinized mucosa in the right central and lateral incisor sites for later Fig. 10.24 The two harvested full palatal mucosal grafts before adap-
implant placement tation and fixation to the recipient sites
220 10 Hard and Soft Palate
Palatal Mucosa Thickness: Assessment region, with the thinnest area at the first molar region and the
with Bone Sounding thickest at the second premolar region. There was no signifi-
cant difference in the thickness of the mucosa between the
Studer et al. (1997) measured the PMC in 31 patients using groups with high or low palatal vaults. The canine to premolar
periodontal probes following palatal local anesthesia. The region appeared to be the most appropriate donor site since the
mucosal thickness was studied at three levels (3, 8, and mucosa demonstrated uniform thickness in this area.
12 mm from the gingival margins) at the midpoint of canines Barriviera et al. (2009) evaluated the thickness of the PMC
through to second molars. The thinnest mean depth was using coronal CBCT scans with the subjects biting on a spatula
recorded over the palatal root of the first molar (1.8 ± 0.8 mm). to avoid the tongue from touching the palatal mucosa during
All measurements obtained at the 12-mm level were signifi- image acquisition. The thickness was measured at four levels
cantly thicker than those measured at the other levels. No (2, 5, 8, and 12 mm) from the gingival margin. No significant
significant differences were observed comparing the mean differences were observed comparing the data from males and
values of males and females. females, but subjects older >40 years tended to have thicker
Using a similar method, Wara-aswapati et al. (2001) mucosa. In all teeth, the palatal mucosa was thicker at higher
assessed the thickness of the PMC in two different age groups levels (8 and 12 mm) compared to those closer to the gingival
comprising 32 subjects with a mean age of 16.8 years (range margin (2 and 5 mm). Measurements performed at 2 mm from
14–21 years) and 30 subjects with a mean age of 38.7 years the gingival margin were similar in all teeth. However, the pala-
(range 30–59 years). The mean thickness of PMC ranged from tal mucosa was thicker at intermediate levels (5 and 8 mm) in
2.0 to 3.7 mm. The younger age group had significantly thin- canines and both premolars compared to molars. With the
ner mucosa (mean 2.8 0.3 mm) than the older age group (mean exception of canines, all other teeth presented the thickest pala-
3.1 0.3 mm). Females had thinner mucosa than males in the tal mucosa at 12 mm of measurement.
same age group, but the difference was not statistically signifi- Marquezan et al. (2012) assessed the palatal mucosa in 36
cant. Overall, the thickness of palatal mucosa increased from patients (mean age 23.6 ± 11.9 years) in 20 locations using CBCT
the canine to second molar areas and in the sites furthest from imaging as follows: in the midline, 3 and 6 mm bilaterally to the
the gingival margin toward the mid-palate (with the exception midline at 4, 8, 16, and 24 mm posterior to the incisive foramen.
of the first molar area, where significantly decreased thickness The mucosal thickness was greater at anterior than posterior sites
was observed). The authors concluded that the canine and pre- as well as lateral compared to midline sites. The mean thickness
molar areas appear to be the most appropriate donor site for in the midline ranged from 1.33 mm (posterior sites) to 2.92 mm
harvesting procedures in both young and adult individuals. (anterior sites), at the 3-mm level lateral to the midline from
Bone sounding using a periodontal probe was also used by 1.75 mm (posterior sites) to 3.38 mm (anterior sites), and at the
Stipetic et al. (2005) to assess the palatal mucosa in 102 indi- 6-mm level lateral to the midline from 2.54 mm (posterior sites)
viduals (20–49 years old). Measurements were taken from to 5.33 mm (anterior sites). Ueno et al. (2011) compared the val-
canines to third molars at three levels from the gingival margin ues of the thickness of the oral mucosa obtained with CT and
(3, 7, and 11 mm). The mucosa was significantly thicker in bone sounding with reamers in five cadaveric heads. Overall
males than in females in all regions, except for the first molar mean values of mucosal thickness were 3.12 ± 1.43 mm (bone
region and tuberosity. Similar results were obtained for indi- sounding) and 2.83 ± 1.70 mm (CT) demonstrating a strong cor-
viduals with a higher body mass index (>22 kg/cm2). relation of r = 0.90. The overall measurement error was 0.52 mm
Schacher et al. (2010) measured the mucosal thickness with significant correlation coefficients of r = 0.92 (buccal
with cannulas at 8 mm from the gingival margin in 33 healthy mucosa), r = 0.91 (alveolar crest mucosa), and r = 0.85 (palatal
subjects (mean age 27.8 years). The mean thickness was mucosa) comparing physical and radiographic measurements.
lowest in the first molar sites (4.39 1.05 mm) and highest in However, in sites with very thin mucosa, the border between
the second molar sites (5.75 1.78 mm). Women exhibited bone and mucosa could not be differentiated with spiral CT due
thicker mucosa than men in all assessed sites (p < 0.05 for to inadequate resolution of pixel densities.
canine and molar regions).
The Soft Palate actions of the pharynx as the soft palate moves back and
presses posteriorly sealing the oropharynx from the naso-
The main components of the soft palate include five paired pharynx. It may also be involved in finer movements of the
muscles including the palatoglossus, palatopharyngeus, soft palate and pharynx during vocalization (Yamawaki
levator veli palatini, tensor veli palatini, and muscular uvulae 2003).
(Figs. 10.25 and 10.26) (Table 10.6). The soft palate has All muscles of the soft palate are innervated by the vagus
gained considerable interest for its possible role in obstruc- nerve (CN X) except the tensor veli palatini that receives the
tive sleep apnea; however, this involvement remains contro- motor supply from the mandibular nerve through a branch to
versial (Caples et al. 2010). The palatoglossus descends from the medial pterygoid muscle. A recent dissection study on 50
the soft palate to the tongue and forms the palatoglossal arch. Japanese hemisected cadaveric heads demonstrated that a
The palatopharyngeus also arises from the soft palate, runs plexus formed by branches from the glossopharyngeal and
posterior to the palatoglossal arch, and forms the palatopha- vagus nerves was the most frequently motoric innervating
ryngeal arch as it inderdigitates with the superior pharyngeal pattern of the levator veli palatini (Shimokawa et al. 2004).
constrictors (Sakamoto 2015). The tonsillar crypt houses the Siebert et al. (1997) evaluated the vascular supply of the
palatine tonsil, and it is located between these muscles and is soft palate in ten fresh cadaveric heads injecting color latex
contiguous to the tongue. The palatoglossus and palatopha- into the arterial system (Fig. 10.27). The ascending palatine
ryngeus muscles also form the isthmus of the fauces and, branch of the facial artery was 1–1.5 mm in diameter and
when contracted, contact the tongue and soft palate sealing entered the soft palate by crossing over the levator veli pala-
the oral cavity from the oropharynx posteriorly. This action tini. The anterior branch of the ascending pharyngeal artery
occurs spontaneously enabling the infant to breath through was 0.8–1.2 mm in diameter and entered the soft palate
the nose while suckling; an action that can be simulated by slightly more cranial by coursing over the tensor veli and
an adult by sucking the thumb and breathing simultaneously. levator veli palatini muscles. A rich anastomotic network
The palatoglossus muscles also mark the posterior border of existed within the maxilla between the ascending palatine
the oral cavity. A recent study on 50 cadavers has shown that branch of the facial artery, the anterior branch of the ascend-
the palatopharyngeus muscle not only has two longitudinal ing pharyngeal artery, and the alveolar branches of the inter-
fasciculi but also has a transverse fasciculus that appears to nal maxillary artery. Hwang et al. (2009) studied the
provide a sphincter function when closing the pharyngeal microscopic relation of the palatopharyngeus with levator
isthmus (Sumida et al. 2012). veli palatini and superior constrictor in ten Korean cadaveric
The levator and tensor veli palatini muscles are positioned heads. The palatopharyngeus originated from the palatine
contiguous to one another and serve to elevate and tense the aponeurosis and posterior mucosa of the soft palate. The
soft palate thus forming a barrier between the oropharynx majority of muscular fibers did not cross the midline at their
and nasopharynx. The levator veli palatini arises from the origin. As the palatopharyngeus coursed downward and
petrous portion of the temporal bone and the adjoining carti- crossed the levator, it split into anterior and posterior fascic-
laginous portion of the pharyngotympanic tube. The muscle uli and passed on either side of the levator veli palatini.
runs inferomedially passing superior to the superior constric- Below the levator, the two fasciculi united and were inserted
tor muscle of the pharynx inserting into the soft palate and to the medial side of the superior constrictor with dense
serving to elevate the soft palate upon contraction. When act- attachment between the two muscles.
ing from below, the muscle will place tension on the pharyn- Cho et al. (2013a) performed a detailed anatomical study of
gotympanic tube and cause it to open thus assisting in the the soft palate with sagittal plane dissections of ten cadaveric
process equalizing pressure on the tympanic membrane of heads and coronal plane dissections of another ten cadaveric
the middle ear. The tensor veli palatini originates from the heads. The inferior, oral portion of the soft palate consisted of
scaphoid fossa at the base of the pterygoid plate and runs a thick fibrous and fatty layer. This layer became denser and
inferiorly. This muscle then becomes tendinous as it bends thicker toward the midline aponeurosis. The palatoglossus
around the hamulus of the medial pterygoid plate and runs originated from the midline aponeurosis, fanning out as it
horizontally to intersperse with the palatine aponeurosis. As descended to insert into the base of the tongue. It was a thin
a result of its trajectory from the lateral aspect, it serves to muscle (mean width 3.2 ± 1.2 mm) and comprised the full
tense the soft palate (Vrionis et al. 1996). The muscular uvu- palatoglossal arch. The palatopharyngeus was found to be a
lae comprise small fibers arising from the posterior nasal flat muscle attaching to the soft palate and descending into the
spine and passing posteriorly to combine with the mucosa of lateral pharyngeal wall. The tensor and levator veli palatini
the uvula. Its bilateral function is to move the uvula superi- originated both from the inferior aspect of the Eustachian tube
orly but laterally when contracting ipsilaterally. cartilage. The levator veli palatini ran inferoanteriorly to the
An additional contractile element, called Passavant’s midline aponeurosis of the soft palate. The tensor veli palatini
muscle or ridge, serves to encircle the pharynx at the level of coursed downward nearly vertically to wrap around the hamu-
the soft palate, but this is debated. It is believed that this con- lus of the medial pterygoid plate and finally attached to the
nective tissue structure contributes to the sphincter-like aponeurosis of the soft palate. The authors further noted that
224 10 Hard and Soft Palate
the muscles and various structures of the soft palate were muscle ran posteriorly crossing above the sling formed by
embedded and interwoven in a thick fibro-fatty layer, making the levator veli palatini. Then the fibers of the musculus uvu-
it difficult to dissect and analyze them separately. lae that were intermingled with glandular tissue reached the
Sumida et al. (2014) performed an anatomical study of distal tip of the uvula. The function of the musculus uvulae
the muscular uvulae in 27 Japanese cadavers. After originat- enhances velopharyngeal closure by occupying space, modi-
ing from the oral surface of the palatine aponeurosis, the fying stiffness, and extending the velum.
PGA PGA
PPA
Uv
PPA
PtT PtT
PPW
PTT PTT
Left Right
choana choana LVP
TVP TVP
MA
DPA
MA
LPA GPA
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Infratemporal Fossa
11
The infratemporal fossa (ITF) is an irregularly shaped space There is no anatomical floor of the ITF where it commu-
(Table 11.1) on the lateral skull base and largely includes the nicates with the parapharyngeal space and the retromandibu-
region between the posterior maxilla, the lateral part of the lar area (Chap. 13). The exact definition of ITF’s boundaries
sphenoid bone, and the ascending mandibular ramus appears not to be universal with some authors referring to the
(Fig. 11.1). The inner aspect of the ramus contributes to the ITF as the region below the greater wing of the sphenoid
lateral wall of the ITF. The medial boundary of the ITF is bone and lateral to the pterygoid plate, whereas others define
formed by several structures including the lateral pterygoid the ITF as the region below the middle cranial fossa (Vrionis
plate of the sphenoid bone, tensor veli palatini, levator veli et al. 1996; Bejjani et al. 1998; Tiwari 1998; Roche et al.
palatini, and superior pharyngeal constrictor muscles. 2001; Sabit et al. 2002; Joo et al. 2013). The ITF has also
Anteriorly, the ITF is bordered by the posterior aspect of the been defined as a continuation of the temporal fossa between
maxilla (Fig. 11.2). The anterior and medial walls of the ITF the internal surface of the zygoma and the external surface of
are separated superiorly by the pterygomaxillary fissure, the temporal bone and greater wing of the sphenoid bone that
through which the ITF communicates with the pterygopala- is located deep to the ramus of the mandible (Isolan et al.
tine fossa. 2007). Rarely, the pterygopalatine fossa has been defined as
The posterior boundary of the ITF is variously delineated. a part of the ITF (Robert et al. 1989). According to von
Some authors define it as the prevertebral layer of the cervi- Lüdinghausen et al. (2006), the main osseous landmarks of
cal fascia and the underlying muscles (Bejjani et al. 1998). the border area between the infratemporal fossa and the para-
This broad definition includes the structures localized behind and retropharyngeal spaces are the sphenoidal spine and the
the styloid muscles, including the internal carotid artery, pterygoid and styloid processes (Fig. 11.4).
internal jugular vein, and lower cranial nerves. For other In general, the inferior, posteromedial, and superolateral
authors (Roche et al. 2001), these structures belong to the aspects of the infratemporal fossa are exposed and without
parapharyngeal space, and they define the posterior wall of bony walls (Joo et al. 2013). The ITF communicates medi-
the ITF as the articular tubercle of the temporal bone and the ally with the pterygopalatine fossa via the pterygomaxillary
spine of the sphenoid bone while still others define the pos- fissure and superiorly with the temporal fossa (Fig. 11.5).
terior boundary as the tympanic part of the temporal bone Important anatomical structures that run through the ITF
and the styloid process (Vrionis et al. 1996; Sabit et al. 2002; include the mandibular nerve and the maxillary artery with
Joo et al. 2013). their branches. The main muscles of the ITF are the medial
The roof of the ITF is formed by the sphenoid bone that pterygoid muscles (MPM) and the lateral pterygoid muscles
includes the inferior surface of the greater wing that is the (LPM) (Chap. 26), the latter occupying most of the ITF
site of the foramen ovale and foramen spinosum and by the (Vrionis et al. 1996) (Fig. 11.6). The ITF also contains the
lower portion of the temporal bone with the zygomatic pro- otic ganglion and the pterygoid venous plexus that is clini-
cess of the temporal bone marking the upper boundary of the cally relevant since it communicates with the cavernous
ITF (Fig. 11.3). Superiorly and laterally, the ITF is partially sinus (see below). The distance from the zygomatic arch to
separated from the temporal fossa by the infratemporal crest the lateral pterygoid plate provides an approximate value for
formed as a transverse ridge of the greater sphenoid wing but the width of the ITF, and it was assessed in 34 adult skulls.
then communicating directly with the temporal fossa tra- The reported mean distance was 38.2 mm (range 32–45 mm)
versed by the temporalis muscle. (Tiwari 1998).
Table 11.1 Divisions of the infratemporal fossa (ITF) based on Vrionis et al. (1996) and Bejjani et al. (1998)
Divisions Boundaries Content
Pterygomandibular portion1 Anterior: posterior part of maxilla Medial pterygoid muscle, mandibular nerve
Posteromedial: medial pterygoid muscle and its branches, pterygoid venous plexus
and interpterygoid fascia
Lateral: ascending ramus of mandible
Maxillopharyngeal portion2: Anterolateral: medial pterygoid muscle Lateral pterygoid muscle, parotid gland, facial
prestyloid region and interpterygoid fascia nerve, external carotid artery and its branches
Posterior: styloid diaphragm3
Medial: parapharyngeal space
Maxillopharyngeal portion2: Anterior: styloid diaphragm3 Internal carotid artery, internal jugular vein,
retrostyloid region Posterior: prevertebral layer of cervical initial extracranial courses of CN IX–XII4
fascia and underlying muscles
Medial: parapharyngeal space
1
Pterygomandibular portion = anterolateral part of ITF
2
Maxillopharyngeal portion = posteromedial part of ITF
3
Styloid diaphragm is formed by anterior belly of digastricus muscle, the styloid muscle group (styloglossus, stylohyoid, and stylopharyngeus), the
stylohyoid and stylomandibular ligaments, and the stylopharyngeal fascia (Bejjani et al. 1998)
4
Cranial nerves: glossopharyngeus (CN IX), vagus (CN X), accessory (CN XI), hypoglossal (CN XII)
PTPlp
FOv
FSp
Condylar fossa of
temporal bone
Fig. 11.1 Inferior view of a dry skull showing outline of left infratem-
poral fossa (dotted area). FOv foramen ovale, FSp foramen spinosum,
PTPlp lateral plate of pterygoid process
11 Infratemporal Fossa 231
PTPlp
MP
PTPlp
STP
MT
PTPmp
M2
Ham
232 11 Infratemporal Fossa
SSP
MP
PTPlp
STP
2
ITF
Mandibular Nerve
Ramus (resceted)
MT
FOv
FSp
Lateral aspect
of greater wing
of sphenoid bone
Mandibular Nerve 235
Fig. 11.9 Axial CBCT view at the level of the foramina ovalia and
foramina spinosa in a 33-year-old male. FOv foramen ovale, FSp fora-
men spinosum, ITF infratemporal fossa, MS maxillary sinus, PPF pter-
ygopalatine fossa, PTC pterygoid canal, SPS sphenoid sinus Orbit Orbit
MS MS
ITF ITF
PPF PPF
SPS
FOv FOv
FSp
PTC FSp
Condyle
Condyle
MPM
IAN
LN
236 11 Infratemporal Fossa
Mandibular Nerve: Anterior Trunk trunk of the mandibular nerve (Fig. 11.11). The buccal
branch of V3 proceeds between the two muscle bellies of the
The anterior trunk of the mandibular nerve gives rise to the LPM descending deep and then anteriorly (Piagkou et al.
motoric branches supplying the masticatory muscles includ- 2011a, b). The buccal nerve of V3 (Chap. 14) is a sensory
ing the masseteric nerve, two to three deep temporal nerves, branch innervating the mucous membrane of the cheek and
and the branches to the LPM and MPM (Vrionis et al. 1996). gingiva but also the skin over the buccinator muscle (Isolan
In addition, the long buccal nerve originates from the anterior et al. 2007; Piagkou et al. 2011a, b).
STA
TBz
ZB LPMsh
CM
LPMih
LBN
Ramus
Fig. 11.11 Dissection of a left lateral aspect of a cadaveric head show- LPMih inferior head of lateral pterygoid muscle, LPMsh superior head
ing the long buccal nerve emerging between the two heads of the lateral of lateral pterygoid muscle, STA superficial temporal artery (tortuous),
pterygoid muscle (the zygomatic arch and the coronoid process have TBz zygomatic process (resected anteriorly) of temporal bone, ZB
been resected). CM condyle of mandible, LBN long buccal nerve, zygomatic bone (resected posteriorly)
Mandibular Nerve: Posterior Trunk 237
Mandibular Nerve: Posterior Trunk the ITF by dissecting 36 cadaveric heads. In four specimens
(11.1 %), unusual neural connections were observed. In two
The large posterior trunk of the mandibular nerve descends specimens, a communication between the mylohyoid nerve
medial to the LPM and ultimately divides into the auriculotem- and the lingual nerve was observed while in another two speci-
poral, inferior alveolar, and lingual nerves (Figs. 11.12 and mens a communication between the auriculotemporal nerve
11.13). The average length of the posterior trunk from the fora- and the inferior alveolar nerve was noted. The latter communi-
men ovale to the bifurcation into the lingual and inferior alveo- cating branches are thought to convey “hitchhiking” postgan-
lar nerve was 13.5 mm (range 6–32 mm) (Joo et al. 2013). glionic fibers from the otic ganglion to the inferior alveolar
Thotakura et al. (2013) investigated the communications nerve via the auriculotemporal nerve, eventually innervating
between branches of the posterior mandibular nerve trunk in the lower labial glands (Thotakura et al. 2013).
ATNr
ATN
MN
TVP
Auriculotemporal Nerve
Inferior Alveolar Nerve 7.8–24.1 mm) inferior to the foramen ovale (Kim et al. 2004).
The distance between the origin of the lingual nerve and the
The inferior alveolar nerve (IAN) normally descends medial junction of the chorda tympani nerve to the lingual nerve was
to the LPM, passes between the sphenomandibular ligament reported to be on average 11.4 mm (Vrionis et al. 1996) and
and the mandibular ramus where it typically gives rise to the 8.4 mm (range 0–20 mm) (Joo et al. 2013), respectively. The
mylohyoid nerve, and then enters the mandibular canal lingual nerve is discussed in detail in Chap. 19.
through the mandibular foramen (Chaps. 15, 16 and 19)
(Piagkou et al. 2011a, b). The mylohyoid nerve passes for-
ward in a groove along the medial aspect of the mandible. Otic Ganglion
Buch and Agnihotri (2012) reported a recurrent variant
branch of the IAN in 34.3 % of 35 dissected sides of cadav- The otic ganglion comprises autonomic cell bodies embed-
eric heads. The branch emerged from the IAN up to 10 mm ded in the mandibular nerve as it exits the foramen ovale in
below the origin of the mylohyoid nerve and in most cases the infratemporal fossa (Fig. 11.14). The ganglion is situ-
supplied the lower head of the LPM. ated medial to the posterior trunk of the mandibular nerve,
lateral to the tensor veli palatini, anterior to the middle
meningeal artery, and posterior to the MPM. It is a
Lingual Nerve peripheral ganglion of the parasympathetic system.
Topographically, it is intimately related to the mandibular
The lingual nerve is the largest branch of the posterior trunk nerve, whereas functionally it is connected to the glosso-
of the mandibular nerve. The lingual nerve begins its course pharyngeal nerve. The parasympathetic root of the gan-
from the ITF lateral to the medial pterygoid muscle but medial glion is formed by the lesser petrosal nerve that conveys the
and ventral to the IAN. The lingual nerve runs between the preganglionic fibers from the glossopharyngeal nerve usu-
tensor veli palatini and the LPM muscle where it is joined by ally passing through the foramen ovale. The sympathetic
the chorda tympani (Piagkou et al. 2011a, b). The bifurcation root is derived from the sympathetic plexus of the middle
spot of the lingual nerve and IAN was located 14.3 mm (range meningeal artery (Joo et al. 2013, 2014).
FOv
Maxillary Artery superficially to the LPM and in 31.6 % showed a deep course.
In 78.9 %, both sides presented an identical course, and the
The maxillary artery (MA) and the superficial temporal bilateral correlation of the trajectory was very high (odds
artery are the terminal branches of the external carotid artery ratios of 11.2 for right side and 12.2 for left side). No gender
(ECA) (Figs. 11.15 and 11.16). The bifurcation of the ECA differences were observed. Sashi et al. (1996) studied the
is usually located deep to or within the parotid gland approx- course of the MA angiographically in 100 Japanese patients.
imately at the level of the neck of the mandibular condyle. In 93 %, the MA ran deep to the LPM and in 7 %
The MA then courses anterosuperiorly through the ITF to superficial.
reach the pterygopalatine fossa. The diameter of the MA Kim et al. (2010) studied in detail the course of the MA
ranges between 1.6 and 5.6 mm (Otake et al. 2011). The within the ITF dissecting 100 cadaveric specimens and clas-
course of the MA in the infratemporal fossa is variable, but it sified the trajectory of the MA in six patterns relative to the
can be determined accurately with a three-dimensional com- inferior alveolar nerve, lingual nerve, buccal nerve, and
puted tomographic angiogram (Shevel 2013). After originat- LPM. The most common course (61 %) of the MA was
ing from the ECA, the MA is divided into three segments medial to the inferior alveolar nerve and lingual nerve but
(Fig. 11.17): lateral to the LPM and buccal nerve. In 21 %, the MA showed
an identical pattern except that the buccal nerve was lateral
(i) The first or “mandibular” segment runs nearly horizon- to the MA. The remaining cases (18 %) demonstrated four
tal and deep to the mandibular condyle. It courses other variations of the trajectory of the MA.
superficially to the sphenomandibular ligament to reach Hwang et al. (2014) investigated the location of the MA
the inferior margin of the lower head of the LPM. The relative to the LPM and to the mandibular ramus using CT
arterial branches of the first segment of the MA include scans of 100 patients. In 82 %, the MA was positioned lateral
the deep auricular artery, the anterior tympanic artery, and in 18 % medial to the LPM. The contact point between
the middle meningeal artery, the accessory meningeal the MA and the internal surface of the ramus was found to be
artery, and the inferior alveolar artery. located on average 3.6 ± 2.2 mm posterior and 1.7 ± 1.4 mm
(ii) The second or “pterygoid” segment advances obliquely inferior relative to the deepest concavity of the mandibular
either superficial or deep to the lower head of the LPM notch. Bacioglu et al. (2010) assessed the trajectory of the
(see below). Branches of the second segment typically MA relative to the mandibular ramus in 17 adults’ cadaveric
comprise the temporal, masseteric, and pterygoid arter- heads. The mean distance between the MA and the mandibu-
ies to the masticatory muscles and the buccal artery lar notch was 2.9 ± 0.5 mm. The course pattern of the MA at
coursing anteroinferiorly to the cheek. the subcondylar level was supracervically in 41 %, midcervi-
(iii) The third or “pterygopalatine” segment refers to the cally in 29.5 %, and infracervically in 29.5 %.
portion of the MA within the pterygopalatine fossa Guo and Guo (2014) assessed the course of the MA rela-
(PPF). The MA passes between the two heads of the tive to the condyle dissecting the ITF. The MA was found
LPM to reach the pterygomaxillary fissure and to enter between the deep surface of the condyle and the sphenoman-
the PPF (Chap. 12). dibular ligament at a mean distance of 8.3 ± 3.2 mm to the
inferior border of the capsule of the TMJ. Isolan et al. (2007)
Hussain et al. (2008) dissected 44 adult human cadaveric described the course of the MA as always lateral to the buc-
heads to study the course of the MA relative to the LPM. In cal, lingual, and inferior alveolar nerves in eight dissections
68 % (males 71 %, females 65 %), the MA coursed superfi- of the ITF. All specimens also demonstrated a superficial tra-
cially to the lower head of the LPM, while in 32 % it ran deep jectory of the MA relative to the LPM. According to Roda
to that muscle. There were no variations in the course of the and Blanton (1994), the MA is usually located on average
MA comparing right and left sides of the same cadaver in 17.3 mm above the mandibular foramen. However, in cases
either gender. Dennison et al. (2009) assessed the course of with proximal “downward looping” of the MA, that distance
the MA in 53 cases where bilateral dissection had been suc- was diminished to 9.3 mm on average, thus increasing the
cessful. The second part of the MA was found superficial to risk of intra-arterial injection when performing a mandibular
the lower head of the LPM in 57 % (in 70 % of males and in block anesthesia.
39 % of females). One male and female each presented bilat- Daimi et al. (2011) reported a case with branches of the
eral asymmetry. Statistically, the second part of the MA was mandibular nerve forming a loop through which the maxil-
significantly more likely to lie deep to the lower head of the lary artery passed. Occasionally, a division of the MA into
LPM in females than in males, but side was irrelevant. two branches within the ITF has been reported with one
Gulses et al. (2012) evaluated 572 MA in 286 patients branch lying deep and the other superficial to the LPM
using multi-detector CT angiograms. In 68.4 %, the MA ran (Tadokoro et al. 2008).
Maxillary Artery 241
Otake et al. (2011) investigated the course, distances of lar artery, 1.0 ± 0.2 mm; infraorbital artery, 1.0 ± 0.3 mm; and
branching points, and luminal diameters of the maxillary sphenopalatine artery, 1.2 ± 0.2 mm. There were no statisti-
artery and its branches in 28 sides of Japanese adult cadav- cally significant differences comparing right and left sides.
eric heads. In 96.4 % of the specimens, the main trunk of the Joo et al. (2013) assessed the width of the MA at its origin in
MA ran superficial to the LPM. The mean bilateral distances 20 cadaveric hemifaces. The mean diameter of the MA was
from the origin of the MA to its branches were as follows: 3.5 mm (range 2.5–5 mm).
middle meningeal artery, 9.4 ± 5.2 mm; inferior alveolar Maeda et al. (2012) pooled the data of previous studies
artery, 17.3 ± 4.4 mm; posterior deep temporal artery, regarding the positional relationship of the MA and the LPM
29.0 ± 5.7 mm; buccal artery, 48.7 ± 10.6 mm; anterior deep to calculate weighted averages. In Japanese, the course of the
temporal artery, 55.4 ± 6.2 mm; posterior superior alveolar MA was in 92.7 % lateral and in 7.3 % medial to the LPM,
artery, 64.1 ± 8.0 mm; and infraorbital artery, 66.8 ± 9.2 mm. whereas in Caucasians, the percentages were 61.6 and
The mean distance between the origin of the MA and the 38.4 %, respectively. In their own dissection sample of 104
point of entry into the pterygopalatine fossa was Japanese cadaveric heads (208 sides), Maeda et al. (2012)
78.5 ± 9.3 mm. The mean bilateral luminal diameters of the reported a lateral course in 90.4 %, a medial course in 8.2 %,
MA and its branches were as follows: main trunk of MA, and in the remaining 1.4 % (three cadaveric sides) the MA
2.1 ± 0.7 mm; middle meningeal artery, 1.2 ± 0.2 mm; infe- traversed the LPM. According to Pretterklieber et al. (1991),
rior alveolar artery, 0.6 ± 0.1 mm; posterior deep temporal cephalometric parameters and cephalic indices recorded in
artery, 0.7 ± 0.1 mm; buccal artery, 0.6 ± 0.2 mm; anterior 55 individuals failed to be associated with the position of the
deep temporal artery, 0.7 ± 0.2 mm; posterior superior alveo- MA relative to the LPM.
STA
STA TFA
MA
Masseter
PAA
FA
OA
FA
LN
ECA
IAA IAN
LN
SPA
IOA
MMA 3
STA MA
LPMsh
2 DPA
LPMih BA
MA
1
IAA
MPM
ECA
Fig. 11.17 Illustration demonstrating the three segments of the maxil- artery, LPMih inferior head of lateral pterygoid muscle, LPMsh supe-
lary artery. 1 mandibular segment, 2 pterygoid segment, 3 pterygopala- rior head of lateral pterygoid muscle, MA maxillary artery, MMA mid-
tine segment, BA buccal artery, DPA descending palatine artery, ECA dle meningeal artery, MPM medial pterygoid muscle, SPA
external carotid artery, IAA inferior alveolar artery, IOA infraorbital sphenopalatine artery, STA superficial temporal artery
Middle Meningeal Artery 243
MN
ATN
MA
MMA
MA ChT
LN
IAA
IAN
MHN
The accessory meningeal artery arises from the MA if the The ITF is located at the boundary of the head and neck, and
maxillary artery courses deep to the LPM and from the mid- it is one of the most complex anatomical areas of the cranio-
dle meningeal artery if the MA passes superficial to the facial region. Surgical approaches to the infratemporal fossa
LPM. The artery enters the cranial cavity through the fora- are challenging, even for skilled and experienced surgeons
men ovale or sphenoid emissary foramen, an opening occa- (Joo et al. 2013). Tumors that spread to or invade the ITF may
sionally found 2–3 mm medial to the anterior edge of the originate from the floor of the middle cranial fossa (menin-
foramen ovale, which also transmits an emissary vein linking giomas and trigeminal schwannomas), from the nasopharynx
the pterygoid plexus and the cavernous sinus (Joo et al. 2013). (angiofibromas), from the maxillary sinus (carcinomas), and
from the parotid gland (adenoid cystic carcinomas) (Vrionis
et al. 1996). Various surgical techniques and anatomical
Pterygoid Plexus approaches have been developed by neurosurgeons, oral, and
maxillofacial surgeons as well as by ENT specialists. It is
The pterygoid venous plexus (PVP) consists of an extensive beyond the scope of this book to present and discuss the sur-
network of small vascular channels (Fig. 11.19). The PVP gical approaches, and the interested reader is encouraged to
has a superficial portion between the temporal muscle and consult the pertinent literature.
the lateral pterygoid muscle. The deep portion lies between The ITF has also been reported to be a typical region for
the medial and lateral pterygoid muscles posterior to the lat- compression or entrapment neuropathy of the branches of
eral pterygoid plate and surrounding the lingual and inferior the mandibular nerve (Piagkou et al. 2011a, b). Entrapment
alveolar nerves (Vrionis et al. 1996). The PVP receives of motoric branches may result in paralysis or weakness of
venous drainage from the orbit and from all structures sur- the innervated muscle(s), while compression of sensory
rounding the ITF and communicates extracranially with the branches may cause neuralgia, dysesthesia, or loss of taste.
deep facial vein. The PVP communicates with the intracra- Any such symptom may be suspicious of neurovascular
nial cavernous sinus via emissary veins through the sphenoid compression in the ITF (Piagkou et al. 2011a, b). Entrapment
foramen, foramen ovale, foramen spinosum, and foramen of the auriculotemporal nerve may play a role in the patho-
lacerum (Reymond et al. 2005; Isolan et al. 2007; Joo et al. genesis of temporomandibular joint pain syndromes, head-
2013) as well as variant foramina including the emissary aches, as well as pain symptoms or paresthesias within the
sphenoidal foramen and canalis innominatus (Khairnar and external acoustic meatus and auricle. Hypertrophic mastica-
Bhusari 2013). In the cadaver, the pterygoid plexus is often tory muscles, especially the LPM, may reduce the free space
difficult to locate since it is usually positioned around and within the infratemporal fossa, creating favorable conditions
within the LPM (Guo and Guo 2014). for the compression of the auriculotemporal nerve, for exam-
ple (Komarnitki et al. 2012). A tortuous course of the MA
can also lead to its entrapment causing headaches or nerve
irritation presenting with neuralgia (Verma et al. 2014).
The MA is the main source of severe hemorrhage during
maxillectomy and procedures in the subcondylar region of
the mandible including mandibular osteotomies, resection of
TMJ ankylosis, and internal rigid fixation of subcondylar
fractures (Balcioglu et al. 2010; Hwang et al. 2014). In man-
dibular block techniques such as the Gow-Gates or Vazirani-
Akinosi techniques, the site of injection is close to the MA or
its branches, which may result in the inadvertent intra-arterial
injection of the local anesthetic or hematoma (Hussain et al.
2008). According to Dennison et al. (2009), the lack of
awareness of variation of the MA trajectory may lead to
other adverse clinical consequences such as ligation failure
in epistaxis with artery entrapment.
The existence of neural communication between the
mylohyoid nerve and the lingual nerve may serve recovery
Fig. 11.19 Left lateral view of an adult cadaveric head following CT of the lingual nerve following injury by contributing addi-
imaging and 3D rendering of the pterygoid plexus (blue) previously tional sensory innervation of the tongue (Fazan et al. 2007).
injected with latex to highlight cardiovascular features (courtesy of Dr.
Sara Doll, Anatomical Institute, University of Heidelberg, Germany)
A communicating branch from the mylohyoid nerve to the
Clinical Relevance of the Infratemporal Fossa 245
lingual nerve is developmental in origin and assumed to con- event of tooth dislocation into the ITF to avoid severe hemor-
vey proprioceptive fibers from the mylohyoid muscle through rhage, neurologic injury, or further displacement of the tooth.
the lingual nerve. This communicating branch, if present, The patient should be immediately referred to an oral and
might be involved in the coordination of tongue movements maxillofacial surgeon. A detailed radiographic evaluation
with suprahyoid muscles via proprioceptive impulses including three-dimensional imaging is required for precise
(Thotakura et al. 2013). location of the displaced tooth and for choosing the safest
The ITF has been reported as a risk area where an implant surgical corridor for tooth removal (Bertossi et al. 2013).
or tooth may be inadvertently dislodged (Figs. 11.20, 11.21, The ITF also plays an important role regarding arterial and
11.22, and 11.23). Nocini et al. (2013) described a case of venous communications from the oral cavity to the cranium
implant dislocation into the ITF upon implant placement into (Figs. 11.24, 11.25, 11.26, and 11.27). Inadvertent intra-arte-
the pterygoid process using computer-assisted technology. rial injection in the posterior mandible or maxilla may cause
More frequent are reports describing the displacement of a a bolus of local anesthetic to reach the orbit via retrograde
maxillary third molar into the ITF during surgical removal transportation to the maxillary and middle meningeal artery
(Patel and Down 1994; Dimitrakopoulos and Papadaki 2007; and eventually to the lacrimal artery. In case of inadvertent
Gomez-Oliveira et al. 2010; Selvi et al. 2011; Bertossi et al. intravenous application of local anesthetic, it may get via the
2013). One maneuver especially recommended during the pterygoid plexus to the cavernous sinus that is traversed by
surgical removal of a maxillary third molar is to place an several cranial nerves before they enter the orbit. Both path-
instrument posterior to the tooth while extracting it to prevent ways explain occasional ocular complications following
displacement into the ITF (Patel and Down 1994). Attempts intraoral local anesthesia (von Arx et al. 2014).
to retrieve the displaced tooth are not recommended in the
EC
EC
EC
NS
MidC IC
MS
MS
Infratemporal
fossa
IC
IC
M3
NS
M3
Infratemporal
fossa CP
MT
PTPmp
PTPlp
Fig. 11.20 Coronal CBCT image (anterolateral view) showing a high Fig. 11.21 The axial CBCT image (inferior view) demonstrates the
retention of the maxillary left third molar in a 35-year-old female. The intimate relationship of the crown of the retained third molar and the
crown surface is located within the infratemporal fossa. EC ethmoid infratemporal fossa. CP coronoid process, IC inferior concha, MS max-
cell, IC inferior concha, MidC middle concha, MS maxillary sinus, MT illary sinus, M3 third molar, NS nasal septum, PTPlp lateral plate of
maxillary tuberosity, M3 third molar pterygoid process, PTPmp medial plate of pterygoid process
246 11 Infratemporal Fossa
AN
LA
MMA
MA IOA
PSAA
MA
IAA
ECA
ICA
ICA
OpA
AMA
Eyeball
AN
MMA
LA
Fig. 11.25 Illustration of superior view of right orbit
and middle cranial fossa showing the arterial
anastomosis from the middle meningeal artery to the
lacrimal artery (copyright von Arx et al. 2014). AMA
accessory meningeal artery, AN anastomosis, ICA
internal carotid artery, LA lacrimal artery, MMA middle
meningeal artery, OpA ophthalmic artery
248 11 Infratemporal Fossa
OpV
CS
PVP
FV
RV
IJV
MX SPS
AbN
Literature 249
The pterygopalatine fossa (PPF) can be defined as the “con- medially restricted portion that contained the PPG; however,
trol center” of the maxilla since it provides vasculature the definition has expanded to include the full osseous com-
through the maxillary artery as well as somatosensory and partment that accommodates several critically important neu-
autonomic innervation via the maxillary nerve and the ptery- rovascular structures (Daniels et al. 1998).
gopalatine ganglion (PPG) to the midface. Located along the The PPF communicates with multiple anatomic regions
virtual line that separates the viscerocranium and the neuro- (Table 12.1), including the middle cranial fossa via the fora-
cranium, the PPF represents a natural crossroads among ana- men rotundum and the pterygoid canal, the orbit through the
tomic compartments pertinent to skull base, facial, inferior orbital fissure, the nasal cavity via the sphenopala-
intracranial, oral, and neck regions (Roberti et al. 2007). The tine foramen, the oral cavity by way of the pterygopalatine
PPF is located between the palatine bone, i.e., the most poste- canal, and the infratemporal fossa through the pterygomax-
rior part of the upper jaw, and the pterygoid plates of the sphe- illary fissure (Erdogan et al. 2003; Hwang et al. 2011a). In
noid bone (Figs. 12.1 and 12.2). Its shape is a stretched and general, the arterial component of the PPF lies anteriorly
inverted four-sided pyramid with the apex pointing inferiorly. and the neural component lies posteriorly (Morton and
Originally, the term PPF was used only for the uppermost and Khan 1991).
Table 12.1 Summary of openings and their content of the pterygopalatine fossa (PPF)
Opening Location relative to PPF Connection with PPF Vascular content Neural content
Foramen rotundum Posterosuperior Middle cranial fossa Venous plexus Maxillary nerve (V2)
Pterygoid (Vidian) canal Posterior Middle cranial fossa Pterygoid artery and vein Pterygoid nerve
Inferior orbital fissure Anterosuperior Orbit Infraorbital artery and vein Infraorbital nerve;
orbital and zygomatic
branches from
maxillary nerve
Sphenopalatine foramen Medial Nasal cavity Sphenopalatine artery and Nasal branches
vein of maxillary nerve
Palatovaginal canal Superomedial Nasopharynx Pharyngeal branch of Pharyngeal branch
maxillary artery of maxillary nerve
Vomerovaginal canal Superomedial Nasopharynx Unspecified small arteries Unspecified small
nerves
Pterygopalatine canal Inferior Palate Descending palatine artery Greater and lesser
and vein (greater and lesser palatine nerves
palatine arteries and veins)
Pterygomaxillary fissure Lateral Infratemporal fossa Maxillary artery (entering Posterior superior
PPF) alveolar nerve(s)
Posterior superior alveolar
artery (leaving PPF) and
vein
CH CH
PPC
PPF PPF
Osseous Components of PPF 253
Osseous Components of Pterygopalatine attach to the pyramidal process of the palatine bone form-
Fossa ing the posteroinferior boundary of the PPF. The roof of
the PPF is formed by the body of the sphenoid bone.
Daniels et al. (1998) have described the osseous anatomy of the The PPF contains the following structures that are embed-
PPF in great detail with excellent graphic illustrations and CT ded in loose fatty tissue: (I) maxillary division of CN V and its
scans depicting the complex anatomy of the PPF. The reader is branches, i.e., zygomatic nerve, roots to sphenopalatine gan-
encouraged to review their highly pertinent article that is sum- glion, one or two posterior superior alveolar nerves, and infra-
marized subsequently. Briefly, three bones contribute to the orbital nerve, (II) pterygopalatine ganglion, (III) third part of
boundaries of the PPF including the maxillary, the palatine, and maxillary artery and its branches, and (IV) network of veins
the sphenoid bones with the following relationships: accompanying the maxillary artery (Erdogan et al. 2003).
Although the anatomy of the PPF is typically described
• Maxillary bone: The posterior face of the os maxilla in reference to osseous structures, Rusu et al. (2013)
(Figs. 12.3 and 12.4) above the pterygomaxillary suture attempted to relate anatomical variations of the PPF to pat-
forms the anterior boundary of the PPF. terns of pneumatization of its bony walls by adjacent para-
• Palatine bone: While the two bilateral horizontal plates nasal sinuses. Evaluating three-dimensional reconstructions
form the posterior quarter of the hard palate, the vertical of CBCT images of 100 patients, the authors described
perpendicular plates (Figs. 12.5 and 12.6) posteriorly fuse recesses of the sphenoid sinus in the posterior wall of the
with the medial plate of the pterygoid process, contribut- PPF, ethmoidal cells and/or recess of the sphenoid sinus in
ing to the anteromedial boundary of the PPF. the superior wall of the PPF, and ethmoidal cells and/or
• Sphenoid bone: The PPF is delineated posteriorly by the recesses of the maxillary sinus in the anterior wall of the
sphenoid with its base and fused plates (Figs. 12.7 and PPF. Based on these results, the authors described the PPF
12.8). The separated (medial and lateral) pterygoid plates as an intersinus space.
Orbital floor
IOC
zygomatic process
IOG
of os maxilla
PSAF
M3
M3
Fig. 12.4 Posterior view of the right os maxilla showing the anterior
boundary (dotted area) of the pterygopalatine fossa in a dry skull. IOC
posterior entrance to infraorbital canal, IOG infraorbital groove, M3
Fig. 12.3 Posterolateral view of the left os maxilla showing the anterior retained maxillary third molar
boundary (dotted area) of the pterygopalatine fossa in a dry skull. M3
retained maxillary third molar, PSAF posterior superior alveolar foramen
254 12 Pterygopalatine Fossa
os maxilla
PPC
OPvp
OPhp
OPhp
PPP
Fig. 12.5 Posterior view of right palatine bone showing the anterome-
dial boundary (dotted area) of the pterygopalatine fossa in a dry skull.
OPhp horizontal plate of os palatinum, OPvp vertical plate of os palati- PPP
num, PPP pyramid process of palatine bone
Fig. 12.6 Posteroinferior view of the right palatine bone fused to the
os maxilla in a dry skull showing the anteromedial boundary (dotted
area) of the pterygopalatine fossa in a dry skull (compare to Fig. 12.5).
OPhp horizontal plate of os palatinum, PPC entrance to pterygopala-
tine canal, PPP pyramid process of palatine bone
Osseous Components of PPF 255
FR
PTP
PMF
PTC
MSpw
PTP
PTPlp
PMS
PTPmp
Ham PTPlp
MT
PTPmp
Fig. 12.7 Inferolateral view of the left pterygoid process of the sphe- Fig. 12.8 Anterior view of the left pterygoid process of a dry sphenoid
noid bone in a dry skull. Ham hamulus, MSpw posterior wall of maxil- bone. FR foramen rotundum, PTC pterygoid canal, PTP pterygoid pro-
lary sinus, MT maxillary tuberosity, PMF pterygomaxillary fissure, cess of sphenoid bone, PTPlp lateral plate of PTP, PTPmp medial plate
PMS pterygomaxillary suture, PTP pterygoid process of sphenoid of PTP
bone, PTPlp lateral plate of PTP, PTPmp medial plate of PTP
256 12 Pterygopalatine Fossa
SOF
Right middle
OPC
cranial fossa
SOF
FR
FR
PTC PTC
PTP
PTP
Fig. 12.10 Posterior view of the right aspect of a coronally sectioned Fig. 12.11 Anterior view of the right aspect of a dry sphenoid bone.
dry sphenoid bone. FR foramen rotundum, PTC pterygoid canal, PTP FR foramen rotundum, OPC optic canal, PTC anterior opening of pter-
pterygoid process of sphenoid bone, SOF superior orbital fissure ygoid canal, PTP pterygoid process of sphenoid bone, SOF superior
orbital fissure
258 12 Pterygopalatine Fossa
choana
PTPlp
PTPmp
Nasal
cavity
Maxillary sinus
vomer
IFS
PPF
choana
Fig. 12.13 Reformatted
inferolateral CBCT view of FR
the foramen rotundum and PTC
the pterygoid canal. FR
foramen rotundum, IFS
Middle
inferior orbital fissure, PPF
cranial fossa
pterygopalatine fossa, PTC
pterygoid canal
Foramen Rotundum 259
PTPlp
Choanae PTPlp
PTPmp PTPmp
IFS IFS
PPF PPF
FR SPS FR
SPS
260 12 Pterygopalatine Fossa
Pterygoid (Vidian) Canal Fu et al. (2014) assessed the dimensions of the pterygoid
canal in CT scans of 137 patients (median age 53 years). The
The pterygoid canal (Figs. 12.8, 12.10, 12.11, 12.12, 12.13, mean length of the medial canal wall was 13.6 ± 2.2 mm. The
12.14, 12.15, and 12.16), also called the Vidian canal, is a mean distal (PPF side) and proximal (foramen lacerum side)
straight to slightly curved osseous tunnel that runs anteriorly diameter of the canal was 3.5 ± 1.1 mm and 2.9 ± 0.9 mm,
from the anterior margin of the foramen lacerum through the respectively. The opening of the pterygoid canal in the PPF
sphenoid bone usually below the floor of the sphenoid sinus was located on average 5.2 ± 3.2 mm below and 6.1 ± 2.8 mm
to end in the PPF. It lies medial and inferior to the foramen medial to the foramen rotundum. Alvernia et al. (2007)
rotundum. The pterygoid canal transmits the pterygoid artery reported a mean diameter of 3.5 mm derived from anatomi-
and nerve (Fu et al. 2014). Omami et al. (2011) studied the cal specimens and 3.05 mm obtained from CT scans of the
course of the pterygoid canal in coronal CT scans of 300 pterygoid canal. Hwang et al. (2011) analyzed CT images of
patients (mean age 34.6 years). The canal was located within 98 patients and reported a mean diameter of 2.4 ± 0.7 mm for
the floor of the sphenoid sinus in 39.6 %, below the floor in the pterygoid canal. The mean vertical and horizontal dis-
38.3 %, and inside the sinus in 22 % of the cases. Overall, tances on the surface plane of the sphenoid bone between the
26 % of the pterygoid canals showed a bone dehiscence. The pterygoid canal and the foramen rotundum were 5.8 ± 1.9 mm
diameter of the pterygoid canal was assessed in 48 subjects and 8.5 ± 1.9 mm, respectively. According to Kim et al.
(mean age 55 years) by Sepahdari and Mong (2013) using (1996), the mean distance between the pterygoid canal and
CT scans. The mean diameter was 1.4 ± 0.39 mm on the right the lower wall of the sphenoid sinus was 2.2 mm anteriorly
side and 1.5 ± 0.39 mm on the left side. and 2.8 mm posteriorly.
IFS IFS
SPF SPF
PPF PPF
PTC PTC
Body of
sphenoid bone
Inferior Orbital Fissure 261
Inferior Orbital Fissure muscle for lacrimal function and for protruding the eye. It
forms a bridge over the inferior orbital fissure and separates
The inferior orbital fissure (Figs. 12.13, 12.15, 12.16, 12.17, the orbit from the pterygopalatine fossa, the infratemporal
and 12.18), also called sphenomaxillary fissure, is a longitu- fossa, and the temporal fossa (de Battista et al. 2012). Note
dinal opening posterolateral to the orbital floor separating that this muscle should not be confused with Muller’s muscle
the lateral wall of the orbit from its floor along the posterior that inserts into the tarsal plate of the upper eyelid (de Battista
two-thirds of the bony cavity. The fissure is bounded pos- et al. 2011).
terolaterally by the greater wing of the sphenoid bone, later- A morphometric analysis of the inferior orbital fissure in
ally by the zygomatic bone, medially by the sphenoid body 50 human dry skulls was completed by de Battista et al.
and a short segment of the palatine bone, and anteriorly by (2012). The mean length of the fissure was 29.1 mm (range
the maxilla. The inferior orbital fissure is narrower in the 23–35 mm). The authors also divided the fissure into three
center than at the extremities and is wide in its anterolateral segments: (I) posteromedial segment communicating with
end where it is completed by the zygomatic bone (de Battista the PPF (mean length 17.0 mm, range 13–22 mm; mean
et al. 2012). The inferior orbital fissure transmits the infraor- width 2.4, range 1.2–4.2 mm), (II) middle segment commu-
bital nerve and vessels as well as the zygomatic branch of the nicating with the infratemporal fossa (mean length 5.0 mm,
maxillary nerve (Erdogan et al. 2003). Further, the fissure range 3–10 mm; mean width 3.2, range 1.0 -6.0 mm), and
contains smooth muscle fibers belonging to the periorbital (III) anterolateral segment communicating with the temporal
muscle, or Muller’s muscle. This muscle is part of the orbital fossa (mean length 6.5 mm, range 3–11 mm; mean width
connective tissue system and serves both as an accessory 5.0, range 1.9–8.7 mm).
SOF
OPC
IFS IOF
262 12 Pterygopalatine Fossa
IOG
Sphenopalatine Foramen foramen. The shape of the foramen was hourglass-like with
a narrow middle part. In all cases, the anterior border of the
The sphenopalatine foramen (Figs. 12.19 and 12.20) is foramen presented a sharp bony crest. The mean height of
located superomedially within the PPF. The vertical plate of the foramen measured 6.1 mm (5.2–6.8 mm). The mean
the palatine bone has two processes superiorly including the width was assessed in three locations with a mean inferior
orbital process anteriorly and the sphenoidal process posteri- dimension of 2.5 mm (2.4–2.5 mm), mean middle dimen-
orly. These processes articulate with the body of the sphe- sion of 1.9 mm (1.6–2.1 mm), and a mean superior dimen-
noid bone forming the sphenopalatine foramen (Morton and sion of 3.1 mm (2.7–3.7 mm). The sphenopalatine foramen
Khan 1991). Others have located the foramen at the junction was located at a mean distance of 18.3 mm (15.1–20.9 mm)
of the sphenoid floor as it disappears laterally and transitions above the horizontal plate of the palatine bone and 13.0 mm
with the medial pterygoid plate (Zheng et al. 2014). Its nasal (9.0–14.9 mm) above the horizontal lamina of the inferior
side is located at the distal end of the superior meatus nasal turbinate.
(Flanagan 2005) or at the posterior border of the middle tur- Hwang et al. (2011) analyzed 98 CT scans and reported a
binate (Chiu 2009). The sphenopalatine foramen transmits mean diameter of 5.3 ± 1.3 mm for the sphenopalatine fora-
the artery and vein of the same name as well as the nasal men. The distance from the posterior edge of the maxillary
branches of the maxillary nerve (Erdogan et al. 2003). sinus ostium to the anterior edge of the sphenopalatine fora-
In a study of 12 dry adult skulls Prades et al. (2008) men was determined in 50 human cadaveric sagittally sec-
assessed the size and dimensions of the sphenopalatine tioned heads and measured 23.8 mm (Shires et al. 2011).
Sphenopalatine Foramen 263
SPF
PMF
PTP
PMS PTPlp
Ham
SPF
Middle meatus
The palatovaginal canal, also known as the pharyngeal canal, The vomerovaginal canal is a small vascular channel that is
lies between the sphenoid process of the perpendicular plate of rarely documented but observed at the boundary of the vagi-
the palatine bone and the vaginal process of the sphenoid nal process of the sphenoid bone and the ala vomeris. It runs
bone. The canal passes from the inferomedial aspect of the from the superomedial wall of the PPF to the nasopharynx
posterior wall of the PPF through the floor of the sphenoid (Chen et al. 2010). It conveys unspecified small nerves and
sinus to terminate beneath the pharyngeal mucosa (Chen et al. arteries.
2010; Omami et al. 2011). It transmits the pharyngeal artery
and the pharyngeal nerve. Rumboldt et al. (2002) examined
the frequency of the palatovaginal canals using CT imaging. Pterygopalatine Canal
The canal was observed on at least one side of 88 patients for
a frequency of 58.7 %. Unilateral complete canals were found The pterygopalatine canal (Figs. 12.6 and 12.21) is the infe-
in 14 patients (9.3 %) and unilateral semicanals were identified rior continuation of the tapering PPF and runs inside the pos-
in 17 individuals (11.3 %). Bilateral complete canals were terior portion of the os maxilla within the posterior wall of
reported for 24 patients (16 %) while bilateral semicanals were the maxillary sinus. Shortly after entering the maxillary
detected in 11 patients (7.3 %). One complete canal and one bone, the canal divides into the greater and lesser palatine
semicanal were identified in 22 patients (14.7 %). canals (Chap. 10).
The maxillary artery, formerly referred to as the internal The posterior superior alveolar artery (PSAA) is the first
maxillary artery, passes over the lateral pterygoid muscle in branch originating from the maxillary artery within the
the infratemporal fossa (Chap. 11) and enters the PPF PPF. The PSAA courses along the posterolateral surface of
through the pterygomaxillary fissure in an anterior, medial, the os maxilla before typically dividing into two or multiple
and upward direction (Kwak et al. 2010) (Fig. 12.22). extra- and intraosseous branches. The PSAA originated from
According to Li et al. (1996), who exposed the pterygomax- the maxillary artery on average at a horizontal distance of
illary region in eight cadavers, the maxillary artery enters the 13.4 mm (range, 8–22.8 mm) from the medial wall of the
PPF on average 16.6 mm (range 13–21 mm) above the nasal maxillary sinus (Kwak et al. 2010). In 48 % of cases, the
floor. The portion of the maxillary artery within the PPF is PSAA and the infraorbital artery branched from a short com-
referred to as the third or pterygopalatine portion of the max- mon trunk originating from the maxillary artery, whereas in
illary artery. From the pterygomaxillary fissure (lateral area the remaining 52 % of cases they branched separately from
of PPF) to the medial area of the PPF, usually five branches the maxillary artery. The PSAA is discussed in detail in
arise from the maxillary artery in the following order: the Chap. 8.
posterior superior alveolar artery, the infraorbital artery, the
artery of the pterygoid canal, the descending palatine artery,
and the sphenopalatine artery (Choi and Park 2003). These Infraorbital Artery
authors also evaluated the course of the maxillary artery and
the branching pattern within the PPF dissecting 21 sides of The infraorbital artery is considered the artery of the mid-
unfixed cadaveric heads. Before branching, the maxillary face. It originates from the maxillary artery in the
artery had a mean external diameter of 3.2 ± 0.6 mm (range anteromedial part of the PPF. The infraorbital artery runs
2.2–4.1 mm). The mean distances from the most inferior anteriorly to enter the infraorbital groove and canal to run
point of the pterygomaxillary junction to the branching below the orbit, and eventually exits the infraorbital fora-
points from the maxillary artery were 15.2 ± 2.4 mm for the men (Chap. 6). In 50 dissected human adult cadaveric
posterior superior alveolar artery, 32.2 ± 3.7 mm for the heads, the point at which the infraobital artery emerged
infraorbital artery, and 24.8 ± 2.8 mm for the descending from the maxillary artery was located 13 mm (range, 6.2–
palatine artery. After 4–5 mm, the latter divided into the 22.8 mm) lateral to the medial wall of the maxillary sinus
greater and lesser palatine arteries at a mean distance of and 14.4 mm (range, 7.1–26.3 mm) from the superoposte-
19.5 ± 3.7 mm above the most inferior point of the pterygo- rior point of the medial wall of the maxillary sinus (Kwak
maxillary junction (Choi and Park 2003). et al. 2010).
266 12 Pterygopalatine Fossa
FR ION
GPT
MX
MX SPF
PPG
ICA with *
sympathetic plexus DPN
PTC
GPN
LPN
FR
MX
MA
MSpmw
Artery of the Pterygoid Canal et al. (2008) evaluated the sphenopalatine artery in 12
cadaveric sides and found that the artery divided into two
The artery of the pterygoid canal, also called the Vidian branches either inside (66.7 %) or outside the sphenopala-
artery, arises from the maxillary artery in the PPF and enters tine foramen (33.3 %). The posterior lateral nasal artery
the pterygoid canal coursing posteriorly to supply the region (mean diameter 1.80 ± 0.20 mm) coursed inferiorly, and the
and terminate as anastomotic branches communicating with nasal septal artery (mean diameter 1.80 ± 0.20 mm) ran
the ascending pharyngeal artery of the external carotid. A superiorly. One or two smaller collateral branches (diameter
second vessel, the Vidian branch of the pterygovaginal artery less than 1 mm) were observed to the superior and/or the
(also known as mandibulovidian artery), arises from the middle turbinates originating from the stem of the main
ascending petrous portion of the internal carotid artery (ICA) branches.
near the opening of the pterygoid canal at the margin of the
foramen lacerum. Although the maxillary component of the
Vidian artery is typically the more dominant of the two, a Neural Structures of Pterygopalatine Fossa
collateral circulatory pattern can be established between the
intracranial and extracranial carotid systems, in particular Maxillary Nerve
serving to reconstitute the petrous portion of the ICA or
occasionally the distal portion of the maxillary artery in the The maxillary nerve enters the PPF through the foramen rotun-
event of occlusion (Takeuchi et al. 2005; Siddiqui and Chen dum (Fig. 12.22) and courses superolaterally to interdigitate
2009). with the pterygopalatine ganglion. Within the PPF, the zygo-
matic branch of the maxillary nerve gives off two branches
including the zygomaticofacial and the zygomaticotemporal.
Descending Palatine Artery The maxillary nerve runs into the infraorbital groove and con-
tinues as the infraorbital nerve (Roberti et al. 2007). Other
The descending palatine artery originates from the maxil- branches of the maxillary nerve include orbital branches pass-
lary artery within the PPF either proximally or distally ing via the inferior orbital fissure and supplying the sphenoid
(Morton and Khan 1991), resulting in different branching sinus and the ethmoidal air cells. Nasal nerves originating from
patterns (see above). The descending palatine artery travels the maxillary nerve leave the PPF through the sphenopalatine
a few millimeters within the pterygopalatine canal before foramen to innervate the nasal cavity. Finally, the greater and
dividing and entering the greater and lesser palatine canals. lesser palatine nerves conducting sensory fibers from the max-
The arteries travel approximately 10 mm within the canal in illary nerve course through the PPG and then pass through the
an inferior, anterior, and slightly medial direction to the pterygopalatine canal and via the greater and lesser palatine
nasal floor and then exit the greater and the lesser palatine canals to the hard and soft palate (see Chap. 10).
foramina (Chap. 10) (Li et al. 1996). The descending pala- Moiseiwitsch and Irvine (2001) measured the distance
tine artery was found to branch from the maxillary artery on from the reflection of the buccal sulcus (fold of vestibule) lat-
average at a horizontal distance of 6.7 mm (range eral to the maxillary second molar to the trunk of the maxil-
0–15.6 mm) from the medial wall of the maxillary sinus lary nerve within the PPF in 47 human adult cadaveric heads.
(Kwak et al. 2010). The mean distance of what they called the pterygopalatine
fissure was 36.7 mm at an approximately 60° angle to the
occlusal plane. Males had on average a 3 mm longer distance
Sphenopalatine Artery than females, and the difference was statistically significant.
The authors suggested using such an approach for a full max-
The sphenopalatine artery originates from the maxillary illary nerve block instead of extraoral techniques or the nee-
artery within the PPF and enters the nasal cavity through the dle advancement through the greater palatine canal.
sphenopalatine foramen. The sphenopalatine artery is con-
sidered the terminal branch of the maxillary artery. After
passing through the foramen, it typically divides into the Pterygopalatine Ganglion
posterior lateral nasal artery supplying the lateral wall of the
nasal cavities including the turbinates and the nasal septal The pterygopalatine ganglion (PPG) (also termed spheno-
artery, also known as the sphenopalatine artery proper, that palatine ganglion or Meckel’s ganglion) is the largest of all
arches over the roof of the nasal cavity and then descends four cranial parasympathetic ganglia. The PPG is lodged in
along the wall of the nasal septum (Flanagan 2005; Morton a niche of the posterosuperior portion of the PPF just ante-
and Khan 1991; Prades et al. 2008). The septal nasal artery rior to the pterygoid canal (Roberti et al. 2007), behind the
terminates as the nasopalatine artery (see Chap. 7). Prades PPF segment of the maxillary artery (Zheng et al. 2014),
268 12 Pterygopalatine Fossa
and opposite the sphenopalatine foramen (Lovasova et al. Luvasova et al. (2013) microdissected 20 human adult
2013). The PPG has three major roots (Fig. 12.23) cadaveric heads to study the PPG. The 3–4 mm ganglion was
including: triangular in 30 % and conical in 70 % of the cases. It was
I. A sensory root of the maxillary nerve that enters the gan- always situated below the maxillary nerve, opposite the
glion directly from superomedially and without synapsing. sphenopalatine foramen, and anterior to the pterygoid canal.
II. A sympathetic root comprising postganglionic fibers Alvernia et al. (2007) evaluated the PPG in five sides of three
from the superior cervical ganglion that arises from the cadaveric heads using skull base approaches and microsurgi-
internal carotid plexus and forms the deep petrosal nerve cal dissection techniques. CT imaging was performed after
entering the ganglion posteromedially. marking the ganglion. The mean diameter of the ganglion
III. The parasympathetic preganglionic fibers from the ner- was 3.6 ± 0.6 mm (range 2.95–4.1 mm). The mean distance
vus intermedius of cranial nerve VII via the greater from the anterior opening of the pterygoid canal to the PPG
(superficial) petrosal nerve. It exists as one of six named was 2.7 ± 0.3 mm and from the foramen rotundum
petrosal nerves (Tubbs et al. 2009). The greater petrosal 4.7 ± 1.1 mm. There was no statistically significant differ-
nerve combines with the deep petrosal nerve to form the ence between the anatomical and CT-based measurements.
nerve of the pterygoid canal that continues to the PPG
(Lovasova et al. 2013; Oomen et al. 2012; Zheng et al.
2014). Sympathetic Distribution
Within the Pterygopalatine Fossa
The PPG is unique because of its parasympathetic neuro-
nal circuitry and its relationship to the maxillary branch of Sympathetic input to the PPF is considered to be via the deep
the trigeminal nerve (CN V). The facial nerve (CN VII) uses petrosal nerve. Rusu and Pop (2010) microdissected 10 adult
the fifth cranial nerve as a structural vehicle analogous to a human cadaveric heads to investigate the sympathetic course
“freeway” for its postganglionic parasympathetic fibers through the PPF. Tissue samples were removed from the PPF
(Khonsary et al. 2013). for histological and immunohistochemical analysis. The
According to Roberti et al. (2007), distributed neural rami authors demonstrated that the sympathetic entry to the PPF
from the PPG are divisible into four groups including: ascend- uses both the path of the external carotid artery via the maxil-
ing (or orbital rami), posterior (or pharyngeal rami), internal lary artery plexus and the internal carotid artery plexus via
(or nasal rami), and descending (or palatine rami). the deep petrosal nerve supplying the PPG.
Communicating rami connect the maxillary nerve to the infe- The sympathetic exit from the PPF uses the neural scaf-
riorly located PPG. The PPG receives sympathetic and para- folding of the PPG branches but also the arterial scaffold-
sympathetic fibers via the Vidian nerve. Such nerve, formed ing (Rusu and Pop 2010). Fibers forming a plexus around
by the fusion of greater and deep petrosal nerves at the level of the maxillary artery were also reported by Lovasova et al.
the lacerated foramen, enters the PPF through the pterygoid (2013); however, the authors speculated that those sympa-
(Vidian) canal along with the Vidian branch of the maxillary thetic fibers were derived from the deep petrosal nerve and
artery (Roberti et al. (2007). Preganglionic parasympathetic not from the external carotid plexus via a maxillary artery
facial nerve fibers synapse in the PPG, while postganglionic plexus.
sympathetic fibers from the superior cervical ganglion and
sensory fibers from the maxillary nerve pass through the gan-
glion without synapsing (Oomen et al. 2012). Postganglionic Parasympathetic Distribution
fibers from the PPG reach the lacrimal glands and the glands Within the Pterygopalatine Fossa
of the mucous membranes of the nasal cavity, nasopharynx, as
well as hard and soft palate (Erdogan et al. 2003). The preganglionic parasympathetic neurons arise from the
Rusu et al. (2009) dissected 20 human adult cadaveric lacrimal subdivision of the superior salivatory nucleus in the
heads to study the morphology of the PPG using additional pons and form the greater petrosal nerve via the nervous
staining and immunohistochemistry. In 70 %, of the cases, intermedius of the facial nerve (CN VII) traversing but not
the PPG appeared as a single macroscopic structure with a synapsing at the geniculate ganglion. The greater petrosal
conical shape located inferiorly and medially to the maxil- nerve continues over the internal carotid artery at the distal
lary nerve along the medial wall of the PPF. In the remain- carotid canal to enter the pterygoid canal at the foramen lac-
ing 30 % of the specimens, the PPG appeared partitioned erum, therefore entering the posterior medial aspect of the
with a superior portion close to the maxillary nerve and an PPF. It synapses with the postganglionic neurons within the
inferior portion at the origin of the greater palatine nerve. PPG. These fibers innervate all craniofacial glands inner-
The latter was always found to be the thickest connecting vated by branches of the maxillary nerve except the parotid
nerve to the PPG. (Khonsary et al. 2013). These include:
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Retromandibular Area
13
The retromandibular area (Fig. 13.1) as described here is fascia, platysma, and superficial cervical fascia (Candirli et al.
rarely addressed in textbooks. It is a diffuse region located 2014). Typical anatomical structures of the retromandibular
behind the inferior portion of the mandibular ramus, but lack- area include the lower portion of the parotid glands (Chap.
ing specific boundaries except the posterior margin of the 4); the muscles originating from the styloid process; the glos-
ramus. Superiorly, the retromandibular area is continuous sopharyngeal nerve (CN IX), hypoglossal nerve (CN XII),
with the infratemporal space (Chap. 11), medially it extends and vagus nerve (CN X); and the external and internal carotid
to the retropharyngeal space, and inferiorly it connects to the arteries (Chaps. 4 and 23). The muscles and ligaments origi-
lateral cervical space. Superficially, the retromandibular area nating from the styloid process have a common function in
is covered by the skin of the neck, external fat layer, superficial lifting the aerodigestive elements upward and backward.
MA masseter
STA
FA
FA
ECA lower mandibular border
submandibular
Fig. 13.1 Dissection of the right gland
side of a cadaveric head showing FA
the retromandibular area (dotted
white line) with the parotid gland DgMab
DgMpb SHM
and the ramus removed. DgMab
anterior belly of digastric muscle,
DgMpb posterior belly of SHM
digastric muscle, ECA external
carotid artery, FA facial artery,
MA maxillary artery, SHM
stylohyoid muscle, STA
superficial temporal artery
Styloid Process cesses from cadavers and dry skulls. The mean length was
22.5 ± 4.2 mm. The incidence of an elongated styloid pro-
The styloid process (g, stylos = pillar) is a spiny process cess was 3.3 %, with a mean length of 36.1 ± 6.1 mm.
located at the bottom of the temporal bone just anteromedial 3D imaging has also been used to evaluate the styloid
to the stylomastoid foramen and lateral to the jugular fora- process (Figs. 13.9, 13.10, 13.11, 13.12, and 13.13). In a
men and carotid canal (Okur et al. 2014) (Figs. 13.2, and CBCT study of 208 patients, the mean length of the non-
13.3). In fact, the styloid process is the most inferior structure elongated styloid process was 20.2 mm ±5.6 mm in males
of the temporal bone. The styloid process points inferoante- and 21.1 ± 4.2 mm in females, whereas the mean length
riorly and it is slightly angulated medially. The mean length of elongated styloid process was 36.2 ± 4.8 mm in males
of the styloid process ranges between 20 and 30 mm, but is and 38.1 ± 8.4 mm in females, respectively (Öztunc et al.
considered elongated when it exceeds 30 mm (Figs. 13.4 and 2014). No significant gender effect was observed. The same
13.5) (Balcioglu et al. 2009). Calcification of the stylohyoid study also determined the angle of the inferomedially ori-
ligament may also result in elongation (Öztunc et al. 2014). ented styloid process in the coronal plane. The mean angle
The tip of the process is located lateral to the pharyngeal wall was 68.1 ± 3.8° in elongated cases and 70.0 ± 4.1° in non-
immediately behind the tonsillar fossa. Usually, the styloid elongated cases (p < 0.05).
process lies between the external and internal carotid arteries The length and angles of the styloid process were deter-
(Balcioglu et al. 2009). mined in 100 symptomatic stylalgia patients using 3D
Three thin muscles and two ligaments originate from the CT (Okur et al. 2014). Mean length of the process was
styloid process (see below). Together with the posterior belly 40.7 ± 10.8 mm, while mean medial and anterior angles were
of the digastric muscle, the styloid muscles and ligaments 67.4° (90°–22.6°) and 73.9° (90°–16.1°). The same mea-
form the styloid diaphragm that is considered a key land- surements in asymptomatic patients (control group) were
mark in the retromandibular area. The styloid diaphragm 38.8 ± 6.5 mm, 69.4° (90°–20.6°), and 75.3° (90°–14.7°). The
divides the retromandibular-pharyngeal space into pre- and only significant difference between test and control groups
retrostyloid regions (Prades et al. 2014). The external carotid was observed for the medial angle of the styloid process.
artery passes through the styloid diaphragm; hence the latter A recent study on dry skulls (age range 11–85 years)
is not a continuously closed structure. reported that the length of the styloid process was positively
Panoramic radiography is a clinically accepted imag- correlated with age (Krmpotic Nemanic et al. 2009). In the
ing modality to detect and measure the length of normal 11–20-year age group, the median length of the styloid pro-
or elongated styloid processes (Monsour and Young 1986) cess was 2.3 mm, whereas in the 61–85-year age group, the
(Figs. 13.6, 13.7, and 13.8). In a study evaluating panoramic mean length was 16.3 mm, but showed considerable variabil-
radiographs of 227 patients (mean age 43.4 years, range ity (3–40 mm). According to the authors, changes in length
18–70 years), the lengths of the styloid processes in males and shape of the styloid process reflected altered function of
and females were 25.8 mm and 22.7 mm, respectively. the muscles originating from the styloid process, i.e., lift-
Males had significantly longer processes than females, ing the aerodigestive elements, following the morphologi-
but no side differences were noted (Balcioglu et al. 2009). cal differentiation of the vocal system and the descent of the
In addition, those authors also evaluated 85 styloid pro- aerodigestive tract during puberty (Krmpotic Nemanic et al.
2009).
Styloid Process 273
ECA
LA
SHM
SPM
ECA
274 13 Retromandibular Area
PTPlp
StP
MP
StP
zygomatic arch
EAC
PTPlp
Ham MP
StP StP
Fig. 13.5 Left lateral view of a Ham
dry skull showing bilaterally
elongated styloid processes. EAC
external auditory canal, Ham
hamulus of medial plate of
pterygoid process, MP mastoid
process, PTPlp lateral plate of
pterygoid process, StP styloid
process
Styloid Process 275
StP
StP
left
ramus
left
condyle
right StP
left
ramus
278 13 Retromandibular Area
right
condyle
left StP
right left
ramus ramus
MT
MT
right left
ramus ramus
StP StP
Styloid Process 279
StP
ramus
SCM
HGN
DgMab SHM
hypoid bone
280 13 Retromandibular Area
Muscles Originating from the Styloid Process muscle was 38.1 ± 8.6 mm. The styloglossus ran inferiorly
and medially between the external and internal carotid arter-
The styloid process is considered the main superior osseous ies to insert into the lateral aspect of the tongue near its dor-
landmark for the three muscles of the styloid diaphragm sal surface. The stylopharyngeus coursed inferiorly along the
(Prades et al. 2014). The stylohyoid muscle (Figs. 13.1, side of the pharynx between the superior and middle pharyn-
13.2, 13.3, and 13.14) extends from the styloid process to geal constrictors (Wang et al. 2014).
the junction of the body of the hyoid bone with its greater According to Prades et al. (2014), the stylopharyngeus
horn. It is located anteromedially to the posterior belly of muscle as well as the glossopharyngeal nerve passes through
the digastric muscle. The stylohyoid muscle originates from the superior and middle constrictor muscles at the posterior
the posterior aspect of the styloid process at its base (Prades border of the hyoglossus muscle. This inferior part of the sty-
et al. 2014). The stylohyoid muscle elevates and retracts the loid diaphragm divides the submandibular region anteriorly
hyoid bone. The styloglossus muscle (Figs. 13.2, and 13.3) and the carotid vessels posteriorly, in contrast to the superior
originates from the anterior aspect of the styloid process, part of the styloid diaphragm that divides the parotid gland
runs anteriorly and medially to the stylohyoid muscle, and region anteriorly and the retrostyloid structures posteriorly.
extends into the lateral border of the tongue (described fur- As stated by Prades et al. (2014), the styloid diaphragm can
ther in Chap. 23). The stylopharyngeus muscle (Figs. 13.2 be considered a “hammock” for the parotid and submandibu-
and 13.3) is the most vertical and medial of the three styloid lar glands.
muscles. It arises from the medial surface of the styloid
process, extends downward, and lies superficial to the supe-
rior constrictor muscle but deep to the middle constrictor Ligaments Originating from the Styloid
muscle. The stylopharyngeus muscle descends, mingles Process
with the fibers of the palatopharyngeus muscle, forms the
lateral glossoepiglottic fold, and finally inserts into the The stylohyoid and stylomandibular ligaments (Fig. 13.15)
epiglottic cartilage (Stockwell et al. 1995). According to extend from the styloid process to the hyoid bone and to the
Ozveren et al. (2003), a pyramid is formed by the stylo- posterior aspect of the inner mandibular angle, respectively.
glossus, stylopharyngeus, and stylohyoid muscles. The tip Both ligaments may show calcifications that are visible
of the pyramid is the styloid process. The glossopharyn- radiographically (Fig. 13.16). The stylomandibular liga-
geal nerve (CN IX) enters the medial side of the pyramid. ment (Chap. 25) limits extreme protrusive movement of the
The middle pharyngeal constrictor and hyoglossus muscles mandible, and the stylohyoid ligament stabilizes the vertical
separate the hypoglossal nerve (CN XII) from the glosso- position of the hyoid bone. The stylohyoid complex encom-
pharyngeal nerve in this region. passes the styloid process and the stylohyoid ligament (Okur
The length of the styloglossus and stylopharyngeus mus- et al. 2014). The inferior part of the stylohyoid ligament also
cles was assessed in six fresh human cadaveric heads (Wang serves as the anterior attachment of the middle pharyngeal
et al. 2014). The mean length of the styloglossus muscle was constrictor muscle, mainly of its anterosuperior portion
32.5 ± 6.2 mm, and the mean length of the stylopharyngeus (Sakamoto 2014).
Ligaments Originating from the Styloid Process 281
MF
StML
IMA StHL
hyoid bone
Internal (ICA) and External Carotid Arteries the proximal trunk of the external carotid artery, cephalad,
(ECA) and close to the source of the occipital artery (Hacein-
Bey et al. 2002). However, variations have been described
These large vessels pass through the retromandibular with the ascending pharyngeal artery either arising from
area close to the parapharyngeal space. The bifurcation the ICA or from the occipital artery or even being absent
of the common carotid artery is usually located at the altogether (Wang et al. 2014). After a short common
upper level of the thyroid cartilage (Fig. 13.17). Wang trunk, the ascending pharyngeal artery divides into two
et al. (2014) found that the ECA and ICA were separated major trunks: anteriorly, the pharyngeal trunk, which is
in 92 % of observed cases by the styloid diaphragm, pha- extracranial, and posteriorly, the neuromeningeal trunk,
ryngeal venous plexus, and the glossopharyngeal nerve. which is intracranial and enters the posterior cranial fossa
Within the retromandibular area, the ascending pharyn- through the foramen magnum. The pharyngeal branches
geal artery normally originates from the posterior wall of supply the pharyngeal submucosal spaces and show abun-
PAA
masseter
ECA
FA
OA
MtA
FA
FA
dant arterial anastomoses with the sphenopalatine arterial Clinical Relevance of Retromandibular Area
system (Hacein-Bey et al. 2002).
An elongated styloid process is a typical finding in patients
suffering from Eagle’s syndrome resulting in neck and cer-
Parapharyngeal Space vicofacial pain. A normally long styloid process cannot be
palpated but an elongated process becomes palpable in the
The parapharyngeal space (PPS) (Fig. 13.18), also called tonsillar fossa. However, elongation of the styloid process has
lateral pharyngeal space, is continuous laterally with the not been accepted as a reasonable explanation for Eagle’s syn-
retromandibular area. The medial pterygoid muscle as well drome by some authors (Slavin 2002; Shin et al. 2009). The
as the superior pharyngeal constrictor muscle contributes latter classified Eagle’s syndrome as entrapment of the glos-
to the anterior and medial boundaries of the PPS. The sopharyngeal nerve. Since the glossopharyngeal nerve passes
parotid gland is located immediately on the lateral aspect medial to the stylohyoid ligament at the base of the styloid
of the PPS. pyramid, Ozveren et al. (2003) suggested that the proximity
might cause glossopharyngeal neuralgia in patients without an
elongated styloid process. They advocated that the stylohyoid
ligament may play a role in Eagle’s syndrome and that this
condition should be classified as an entrapment of the glos-
sopharyngeal nerve. Pathologic conditions associated with
the styloid muscles may further cause cervical and pharyn-
geal symptoms (Prades et al. 2014). Others have described the
possibility of compression of the internal carotid artery by the
SCM 4
IJV 3 stylopharyngeus muscle (Tubbs et al. 2010).
2 PVM
Surgical access via the retromandibular area is one of the
ICA
1 most commonly used extraoral approaches for open reduction
PG and internal fixation of fractures of the subcondylar and con-
dylar regions of the mandible (Kempers et al. 1999; Salgarelli
RMV ECA
et al. 2013). Furthermore, the retromandibular approach has
SHM SPM
also been propagated for the placement of a temporomandibu-
PG
SPCM lar joint prosthesis (Candirli et al. 2014) and to reach the deep
SGM PPM parapharyngeal spaces (Prades et al. 2014).
Some case reports have described the occasional but rare
MPM displacement of mandibular, or even maxillary, third molars
PtT
into the parapharyngeal space (Medeiros and Gaffrée 2008;
Ogadako et al. 2011; Lee et al. 2013).
R
Dental infections, mainly from mandibular third molars,
MM PGM may spread to the parapharyngeal space and continue inferi-
orly. Life-threatening complications include airway obstruc-
tion, mediastinitis, or sepsis. A recent study of 17 patients
with severe neck infections showed that the parapharyngeal
space (83 %) was the most commonly affected neck region,
and dental (29 %) and peritonsillar (23 %) abscesses were the
most frequently primary infections (Horvath et al. 2015).
BM
Hacein-Bey L, Daniels DL, Ulmer JL, Mark LP, Smith MM, Strottmann Okur A, Özkiris M, Serin HI, Gencer ZK, Karacavus S, Karaca L,
JM, Brown D, Meyer GA, Wackym PA. The ascending pharyn- Kantarci M, Saydam L. Is there a relationship between symptoms
geal artery: branches, anastomoses, and clinical significance. Am of patients and tomographic characteristics of styloid process? Surg
J Neuroradiol. 2002;23:1246–56. Radiol Anat. 2014;36:627–32.
Horvath T, Horvath B, Varga Z, Liktor B, Szabadka H, Csako L, Liktor Ozveren MF, Türe U, Ozek MM, Pamir MN. Anatomic landmarks
B. Severe neck infections that require wide external drainage: clini- of the glossopharyngeal nerve: a microsurgical anatomic study.
cal analysis of 17 consecutive cases. Eur Arch Otorhinolaryngol. Neurosurgery. 2003;52:1400–10.
2015;272:3469–74. Prades JM, Gavid M, Asanau A, Timoshenko AP, Richard C, Martin
Kempers KG, Quinn PD, Silverstein K. Surgical approaches to man- CH. Surgical anatomy of the styloid muscles and the extracranial
dibular condylar fractures: a review. J Craniomaxillofac Trauma. glossopharyngeal nerve. Surg Radiol Anat. 2014;36:141–6.
1999;5:25–30. Sakamoto Y. Gross anatomical observations of attachments of the mid-
Krmpotic Nemanic J, Vinter I, Ehrenfreund T, Marusic A. Postnatal dle pharyngeal constrictor. Clin Anat. 2014;27:603–9.
changes in the styloid process, vagina processus styoidei, Salgarelli AC, Anesi A, Bellini P, Pollastri G, Tanza D, Barberini
and stylomastoid foramen in relation to the function of mus- S, Chiarini L. How to improve retromandibular transmasseteric
cles originating from the styloid process. Surg Radiol Anat. anteroparotid approach for mandibular condylar fractures: our clini-
2009;31:343–8. cal experience. Int J Oral Maxillofac Surg. 2013;42:464–9.
Lee D, Ishii S, Yakushiji N. Displacement of maxillary third molar Shin JH, Herrera SR, Eboli P, Aydin S, Eskandar EH, Slavin
into the lateral pharyngeal space. J Oral Maxillofac Surg. KV. Entrapment of the glossopharyngeal nerve in patients with
2013;71:1653–7. Eagle syndrome: surgical technique and outcomes in a series of 5
Medeiros N, Gaffrée G. Accidental displacement of inferior third molar patients. J Neurosurg. 2009;111:1226–30.
into the lateral pharyngeal space: case report. J Oral Maxillofac Slavin KV. Eagle syndrome: entrapment of the glossopharyngeal nerve?
Surg. 2008;66:578–80. Case report and review of the literature. J Neurosurg. 2002;97:216–8.
Monsour PA, Young WG. Variability of the styloid process and stylohy- Stockwell M, Lozanoff S, Lang SA, Nyssen J. Superior laryngeal nerve
oid ligament in panoramic radio- graphs. Oral Surg Oral Med Oral block: an anatomical study. Clin Anat. 1995;8:89–95.
Pathol. 1986;61:522–6. Tubbs RS, Loukas M, Dixon J, Cohen-Gadol AA. Compression of the cervi-
Öztunc H, Evlice B, Tatil U, Evlice A. Cone-beam computed tomo- cal internal carotid artery by the stylopharyngeus muscle: an anatomical
graphic evaluation of styloid process: a retrospective study of 208 study with potential clinical significance. J Neurosurg. 2010;113:881–4.
patients with oro-facial pain. Head Face Med. 2014;10:5. Wang C, Kundaria S, Fernandez-Miranda J, Duvvuri U. A description
Ogadako RM, Woods M, Shah N. Dislodged lower right third molar of arterial variants in the transoral approach to the parapharyngeal
into the parapharyngeal space. Dent Update. 2011;38:631–2. space. Clin Anat. 2014;27:1016–22.
Posterior Mandible
14
The posterior mandible is usually defined as the part of the more frequently have only thin cortices with large trabecular
mandible posterior to the mental foramen (Fig. 14.1). Hence, compartments (Tozoglu and Cakur 2014).
the posterior mandible comprises the posterior body of the Typically, bony and roughened protuberances along the
mandible, the angle, the ascending ramus, the coronoid, and inferior border of the ramus toward the posterior angle of the
the condylar processes of the mandible. The latter two pro- mandible are found on both lateral and medial aspects
cesses are separated by the mandibular (sigmoid) notch and (Figs. 14.3 and 14.4), representing the attachment sites of the
will be discussed in separate chapters (Chaps. 25 and 26). masseter muscle (masseteric tuberosity) and of the medial
The most important internal structure of the posterior man- pterygoid muscle (pterygoid tuberosity) (Chap. 26). The lin-
dible is the mandibular canal (Chap. 16). It crosses the body gula lying anterior to the mandibular foramen is the attach-
of the mandible from the mandibular foramen (Chap. 15) to ment site for the sphenomandibular ligament (Chap. 15)
the mental foramen (Chap. 18). The submandibular fossa (Fig. 14.5). The stylomandibular ligament attaches to the
and the mylohyoid ridge are two prominent structures on the angle of the mandible, between the insertions of the medial
lingual aspect of the posterior mandible (Fig. 14.2). pterygoid and masseter muscles (Lipski et al. 2013).
The body of the mandible is thicker than the ramus with The anterior border of the mandibular ramus is demar-
its broadest part at the level of the oblique and mylohyoid cated from the alveolar process by a prominent bony ridge,
lines, the area that sustains the greatest load. The shape and the external oblique line, curving anteroinferiorly usually as
character of the mandible are also fashioned by muscles and far as the second molar (Fig. 14.6). Posterior to the second or
ligaments that attach to this bone (Lipski et al. 2013). Further, third molar, if erupted, is a flat bony surface, the retromolar
the presence or absence of teeth influences the quantity and trigone. Occasionally, a small foramen called the retromolar
quality of the mandibular bone. Edentate individuals usually foramen is located in this area (Fig. 14.7). It is the opening of
present thick cortices, while edentulous elderly patients the retromolar canal (Chap. 17).
ramus
body of MeF
mandible
angle
MF
MHG
r fossa
ndibula
subma
angle
14 Posterior Mandible 287
CP
CM
CP CM
ALa
MF
EOL La
MHG
MTu
PTu
Fig. 14.4 Right medial aspect of the mandibular ramus and contiguous
Fig. 14.3 Right lateral aspect of the ramus of a dry mandible. ALa structures in a dry mandible. CM condyle of mandible, CP coronoid
antilingula, CM condyle of mandible, CP coronoid process, EOL exter- process, La lingula, MF mandibular foramen, MHG mylohyoid groove,
nal oblique line, MTu masseteric tuberosity PTu pterygoid tuberosity
288 14 Posterior Mandible
SML
LN
lingual mucosa
MHR
LN
MHR
MHN
14 Posterior Mandible 289
CM
CP
ALa
RMF
EOL
MTu
M2
M2
Fig. 14.6 Left lateral aspect of the mandibular ramus and contiguous
structures in a dry mandible. ALa antilingula, CM condyle of mandible,
Fig. 14.7 Superior view of the right retromolar trigone (dotted trian-
CP coronoid process, EOL external oblique line, MTu masseteric tuber-
gle) in a dry mandible demonstrating a retromolar foramen. M2 second
osity, M2 second molar
molar, RMF retromolar foramen
290 14 Posterior Mandible
Dimensions of the Posterior Mandible months. A recent ultrasound analysis of arterial flow in
elderly patients demonstrated that edentulism is associated
Several studies have anatomically or radiographically evalu- with diminished internal vascularization of the mandibular
ated the dimensions of the posterior mandible (Figs. 14.8, body, which, in turn, negatively affects alveolar bone dimen-
14.9, 14.10, 14.11, 14.12, and 14.13); (Table 14.1). In gen- sions (Baladi et al. 2015).
eral, the width of the alveolar crest increases from the pre- The thickness of the ramus was studied in three study
molar region to the molar region, and edentulous sites have samples by Park et al. (2014): group I consisted of 25 patients
markedly thinner ridge widths than dentate sites. Furthermore, (mean age 24.3 ± 2.8 years) without dysgnathism, group II
the buccal cortex is usually thicker than the lingual cortex. consisted of 25 patients (mean age 22.0 ± 3.2 years) with
Schropp et al. (2003) assessed contour changes of the mandibular retrognathism, and group III consisted of 25
alveolar ridge in mandibular premolar and molar sites 1 year patients (mean age 21.3 ± 4.1 years) with mandibular progna-
after tooth extraction in 46 patients (mean age 45 years) thism. The mean minimum and maximum thickness of the
using study casts. The mean width decreased by 6.4 mm ramus was 5.5 ± 1.1 mm and 7.6 ± 1.3 mm in group I,
from 11.5 mm to 5.1 mm over the observation. The greatest 5.1 ± 0.4 mm and 8.8 ± 1.2 mm in group II, and 4.6 ± 0.8 and
amount of tissue loss (4.2 mm) occurred within the first 3 7.0 ± 0.8 mm in group III.
30.3 mm
21.4 -
27.6 mm
Dimensions of the Posterior Mandible 291
18.8 mm
16.5 mm
9.5 - 6.6 -
10.4 mm 8.0 mm
6.0 mm 4.8 mm
buccal lingual
MC
buccal
lingual
Submandibular Fossa 2 mm above the mandibular canal was 2.4 ± 1.1 mm. A
slightly different approach for determining the submandibu-
The submandibular fossa is located on the inner aspect of the lar undercut was reported by Yildiz et al. (2015). They evalu-
mandible below the mylohyoid line (Figs. 14.14, 14.15, and ated CT scans of 77 dry adult human mandibles. The depth
14.16). The fossa extends from the anterior border of the of the submandibular undercut was measured perpendicu-
medial pterygoid muscle below the mylohyoid muscle to the larly to a reference line passing through the most prominent
anterior border of the latter. The content of the submandibu- lingual points of the alveolar process and the basal bone. The
lar fossa is discussed in Chap. 24. The extent of the depres- mean depth of the lingual undercut was 2.7 mm and varied
sion, commonly called the lingual concavity or lingual between 1.1 and 4.6 mm. In 36.5 % of the cases, significant
undercut, is of clinical interest (Figs. 14.17 and 14.18). The concavities (>3 mm) were present.
more concave, the higher the risk of perforation into the sub- Lin et al. (2014) assessed the bone morphology in 1008
mandibular fossa during bone preparation during surgical mandibular second premolar, first molar, and second molar
removal of teeth or implant bed preparation (Figs. 14.19, sites of 237 subjects (mean age 45.6 ± 14.6 years) using
14.20, 14.21, and 14.22). Emes et al. (2015) evaluated the CBCT scans. The undercut type prevailed in the second
position of the lower molar roots in conjunction with the lin- (62.3 %) and first molar sites (57.5 %), whereas the second
gual bone and the floor of the mouth, respectively. CBCT premolar sites most frequently displayed a parallel type
scans of 31 patients were evaluated, measured, and catego- (40.3 %). The most concave point of the lingual undercut
rized. The mean distance between the apex of the most lin- was located at or below the level of the mandibular canal,
gually positioned root and the lingual cortical plate was irrespective of the posterior tooth sites. The depth of the con-
1.03 mm, and the mean distance between the most lingual cavity was greatest in the second molar sites (6.0 ± 1.8 mm)
point on the apical half of the root and the lingual cortical compared to the first molar sites (5.3 ± 1.6 mm) and second
plate was 0.65 mm. Root apices contacted the lingual soft premolar sites (4.3 ± 1.9 mm).
tissue (absence of lingual bone coverage) in 12.5 % of the Yu et al. (2013) assessed the depth of the submandibular
cases, while in another 12.5 % of the evaluated cases, the fossa in 112 patients (mean age 59.9 years) using CBCT
root apices perforated the lingual cortical plate into the floor scans. The depth of the fossa was measured at the level of the
of the mouth. superior margin of the mandibular canal. In the area of first
The concern of lingual perforation is damage to vascular molars, the mean depth of the fossa was 2.08 ± 1.33 mm at a
structures running close to the medial aspect of the subman- mean distance of 4.24 ± 1.43 from the mylohyoid ridge. In
dibular bone (Chap. 22). Since clinical palpation and pan- the second molar sites, the mean depth of the fossa was
oramic radiography are considered unreliable methods to 4.34 ± 2.34 mm at a mean distance of 6.96 ± 2.39 mm from
evaluate the lingual concavity, three-dimensional imaging the mylohyoid ridge. In the second molar sites, the mean
has been recommended by several authors to avoid lingual depth of the fossa was in 92.9 % greater than in first molar
perforation and hemorrhagic, and potentially life-threatening, sites. The authors concluded that implant treatment planning
complications in the floor of the mouth (Parnia et al. 2010; in the posterior mandible, and especially in the second molar
Yu et al. 2013). region, should include three-dimensional imaging to assess
Several radiographic studies using three-dimensional the extent of the submandibular fossa.
imaging evaluated the depth of the submandibular fossa and Chan et al. (2011a) investigated the incidence of lingual
the risk of lingual plate perforation during implant place- plate perforation in edentulous mandibular first molar sites in
ment. Parnia et al. (2010) retrospectively evaluated CT scans a computer-simulated study. Dental implants were virtually
of 100 patients (mean age 44 years) to determine the bone placed using 103 CBCT scans. The cross-sectional morphol-
morphology in the submandibular fossa region. The average ogy of the bone was classified either as parallel, convex (base
depth of the fossa was 2.6 ± 0.85 mm (range 0.4–6.6 mm). A was wider than crest), or undercut. No perforations were
lingual concavity (≥2 mm) was observed in 80 % of the cases observed with 4 × 10 mm or 5 × 10 mm implants. One perfo-
while all patients displayed the horizontal roof of the sub- ration each occurred with 4 × 12 mm and 5 × 12 mm implants
mandibular fossa above the mandibular canal. The mean dis- in an undercut mandible. A total of 2.2–6.1 % of implants,
tance from the posterior margin of the mental foramen to the depending on the size, were found to be ≤ 1 mm from the
deepest point of the fossa was 17.4 ± 8.12 mm. lingual plate, mostly in the undercut group. In a similar study
Chan et al. (2011b) analyzed the cross-sectional morphol- but performed in cadavers, the risk of lingual plate perfora-
ogy of 103 mandibular first molar sites using CBCT imag- tion in the posterior mandible was found to be 5.3 % (one 3.7
ing. The morphology of the mandible was classified into × 10 mm implant out of 19 implants) (Leong et al. 2011).
convex (13.6 %), parallel (20.4 %), and undercut (66 %) The perforation occurred in a first molar site and the fenes-
depending on the shape of the crest and the presence of a tration (2 × 2 mm) was located 8 mm inferior to the alveolar
lingual undercut. The mean depth of the undercut measured crest.
296 14 Posterior Mandible
Braut et al. (2014) evaluated 127 edentulous sites in the 2.4 ± 2.1 mm (range 0.4–9.1 mm). The authors concluded
posterior mandible using CBCT. In 42.5 % of those sites, lin- that the presence of submandibular concavities was asso-
gual undercuts were present. In 10.2 % of sites, the depth of ciated with edentulism.
the undercut was classified as influential for planning the A rare case of implant displacement into the submandibu-
placement of dental implants. lar fossa was presented by Giudice et al. (2015). In a 45-year-
A CBCT analysis of 200 patients showed that a sub- old female, an implant was inserted in the mandibular second
mandibular fossa was present in 98 % of edentulous right molar site but suddenly disappeared into the lingual soft tis-
mandibles and in 88 % of edentulous left mandibles, but sues. Poor implant stability and fracture of the lingual plate
only in 56 % of dentate right mandibles and in 58 % of resulted in implant displacement. An extraoral submandibu-
dentate left mandibles (Kamburoglu et al. 2015). The lar approach was necessary to retrieve the implant from the
calculated mean depth of the lingual undercut was submandibular fossa.
M2 MHG
MHR
LLF
SMF
Submandibular Fossa 297
M2
MHR MF
SMF
SLF
SMF
298 14 Posterior Mandible
M2
MHR
BBP
MHR
BBP
SMF
MC
SMF
MC
Fig. 14.17 Coronal CBCT image showing the lingual concavity of the
submandibular fossa in the second molar area of a 49-year-old female.
BBP buccal bone plate, MC mandibular canal, MHR mylohyoid ridge,
M2 mandibular second molar, SMF submandibular fossa
Fig. 14.18 Coronal CBCT image showing the lingual concavity of the
submandibular fossa in the second molar area of a 73-year-old male.
Note that the implant approaches the mandibular canal as well as the
submandibular fossa. BBP buccal bone plate, MC mandibular canal,
MHR mylohyoid ridge, SMF submandibular fossa
Submandibular Fossa 299
MC SMF
MHR
*
SMF
MC
MC SMF
Fig. 14.20 This coronal CBCT image shows the perforation of the Fig. 14.21 The axial CBCT image shows the fracture of the lingual
lingual bone plate near the tip of the dental implant and its intimate bone plate by the implant body and also radiopaque material (*, prob-
relationship with the mandibular canal. MC mandibular canal, MHR ably a bone fragment) in the submandibular fossa. MC mandibular
mylohyoid ridge, SMF submandibular fossa canal, SMF submandibular fossa
300 14 Posterior Mandible
0.79 -
2.4 cm3
Fig. 14.26 Mean volume of bone grafts harvested from the retromolar
area (see text)
Misch CM. Use of the mandibular ramus as a donor site for onlay bone Tozoglu Ü, Cakur B. Evaluation of the morphological changes in the
grafting. J Oral Implantol. 2000;26:42–9. mandible for dentate and totally edentate elderly population using
Nkenke E, Radespiel-Tröger M, Wiltfang J, Schultze-Mosgau S, cone-beam computed tomography. Surg Radiol Anat.
Winkler G, Neukam FW. Morbidity of harvesting of retromolar 2014;36:643–9.
bone grafts: a prospective study. Clin Oral Implants Res. von Arx T. Intraoral bone harvesting. In: Buser D, editor. 20 Years of
2002;13:514–21. Guided Bone Regeneration. Chicago: Quintessence; 2009. p. 97–121.
Park KR, Kim SY, Kim GJ, Park HS, Jung YS. Anatomic study to Watanabe H, Mohammad Abdul M, Kurabayashi T, Aoki H. Mandible
determine a safe surgical reference point for mandibular ramus oste- size and morphology determined with CT on a premise of dental
otomy. J Craniomaxillofac Surg. 2014;42:22–7. implant operation. Surg Radiol Anat. 2010;32:343–9.
Parnia F, Fard EM, Mahboub F, Hafezeqoran A, Gavgani Yates DM, Brockhoff HC, Finn R, Phillips C. Comparison of intraoral
FE. Tomographic volume evaluation of submandibular fossa in harvest sites for corticocancellous bone grafts. J Oral Maxillofac
patients requiring dental implants. Oral Surg Oral Med Oral Pathol Surg. 2013;71:497–504.
Oral Radiol Endod. 2010;109:e32–6. Yildiz S, Bayar GR, Guvenc I, Kocabiyik N, Cömert A, Yazar F.
Schropp L, Wenzel A, Kostopoulos L, Karring T. Bone healing and soft Tomographic evaluation on bone morphology in posterior mandibu-
tissue contour changes following single-tooth extraction: a clinical lar region for safe placement of dental implant. Surg Radiol Anat.
and radiographic 12-month prospective study. Int J Periodontics 2015;37:167–73.
Restorative Dent. 2003;23:313–23. Yu DC, Friedland BD, Karimbux NY, Guze KA. Supramandibular
Talaat WM, Al Bayatti SW, Dohair DE, Zobeidi MA, Hannouneh canal portion superior to the fossa of the submaxillary gland: a
KM. A CBCT measurement of the mandibular buccal bone thick- tomographic evaluation of the cross-sectional dimensions in the
ness in dentate adults. Oral Surg. 2015;8:38–41. molar region. Clin Implant Dent Rel Res. 2013;15:750–8.
Mandibular Foramen
15
The mandibular foramen is a prominent and important struc- zone of the inferior alveolar nerve block (also called man-
ture of the mandible since it represents the primary portal for dibular or pterygomandibular block). The nerve and its
the mandibular canal and transmits the inferior alveolar neu- accompanying blood vessels are at risk during surgical pro-
rovascular bundle (Figs. 15.1 and 15.2). According to Buch cedures of the ramus, e.g., sagittal split osteotomy, osteosyn-
(2011), the term “mandibular foramen” is a misnomer and thesis, removal of cysts, and tumors (Daw et al. 1999).
should instead be named the “inferior alveolar foramen” to Another hazard is the inadvertent application of anesthetic
more appropriately reflect its function. The mandibular fora- agents and vasopressors into the artery and/or veins (intra-
men is located on the inner aspect of the ramus, approxi- vascular injection) during a mandibular block anesthesia or
mately at the midpoint of the sagittal and vertical dimensions damage to the inferior alveolar nerve by the injection can-
of the ramus. A marked neurovascular bundle enters the nula. A thorough knowledge of the anatomy of the mandibu-
mandible at the mandibular foramen to supply the lower jaw lar foramen and contiguous structures is essential for
and teeth, and therefore, the mandibular foramen is the target successful anesthesia and surgery (Khoury et al. 2011).
MF
MC
MeF
MC
PTPlp
MF
PTPmp
La
CP
CM CP
SN SN
CM
CEC
CEC CEC
SuC
SuC La La
MF
MF
Fig. 15.5 Superior view of the mandibular foramen and the contigu-
ous structures in a dry mandible. CEC crista endocoronoidea, CM con-
MHG dyle of mandible, CP coronoid process, MF mandibular foramen,
La lingula, SN sigmoid notch, SuC sulcus colli
Size and Distances of the Mandibular and from the mandibular foramen to the lower border of the
Foramen ramus at gonion from 18.6 to 42.5 mm.
In an anatomical study of 159 mandibles, significantly
The mean size of the mandibular foramen in adults is approx- larger distances (p < 0.0001) were measured from the foramen
imately 4–5 mm (Jerolimov et al. 1998; Ashkenazi et al. to the anterior, posterior, and lower borders of the mandible in
2011) (Fig. 15.6); (Table 15.1). The survey by Ashkenazi and dentate mandibles than in edentulous mandibles. In contrast,
coworkers has also studied the size of the mandibular fora- the distance between the mandibular foramen and the sigmoid
men related to age showing a mean diameter of 2.97 mm in notch did not differ significantly (p = 0.57) between the two
mandibles of primary dentition, but a mean diameter of samples (Prado et al. 2010). The authors speculated that bone
4.16 mm in mandibles of permanent dentition following resorption along the anterior and/or posterior borders of the
eruption of the third molar. In a study of 100 dry skulls, the ramus occurs due to tooth loss and subsequent reduction of
mandibular foramen was found to have a wide size range masticatory load to the mandible, thus shortening the measured
(1 × 1–6.5 × 5 mm), but was consistently symmetric per indi- distances. However, dental status did not affect the vertical dis-
vidual mandible. In one mandible, the mandibular foramen tance from the mandibular foramen to the mandibular notch.
was divided by a bony spicule doubling the opening (Berge The comparison of anatomical and radiographic measure-
and Bergman 2001). ments showed that distances from the mandibular foramen to all
A large number of studies have assessed the distances borders measured on panoramic radiographs were significantly
from the mandibular foramen to the borders of the ramus larger than those obtained directly from dry mandibles
(Table 15.2) (Fig. 15.7). Excluding data from studies in chil- (Kositbowornchai et al. 2007). Another similar study failed to
dren and adolescents, the mean distance from the mandibular find significant differences between anatomical and radio-
foramen to the anterior border of the ramus ranges from 16.8 graphic measurements. However, only the vertical distance from
to 23.2 mm and to the posterior border from 10.0 to 17.8 mm. the foramen to the sigmoid notch was compared (da Fontoura
With regard to vertical measurements, the mean distance et al. 2002). Kaffe et al. (1994) demonstrated a significant cor-
between the mandibular foramen and the deepest point of the relation of the MF location in panoramic radiographs and the
mandibular or sigmoid notch ranges from 14.1 to 25.2 mm, narrowest anteroposterior dimension of the anatomical ramus.
SN
MF
M3
MC
14.1 -
25.2 mm
10.0 -
17.8 mm
16.8 -
23.2 mm
18.6 -
42.5 mm
Fig. 15.7 Mean values reported in the literature for the distances from
the mandibular foramen to the borders of the ramus projected onto a dry
mandible
314 15 Mandibular Foramen
Relative Position of the Mandibular Foramen were achieved and a Vazirani-Akinosi technique was
Within Ramus administered which proved successful (Cvetko 2014). The
author speculated that a developmental anomaly had caused
Calculation of the relative position of the mandibular fora- the bilateral high position of the MF with extensive and
men within the ramus has shown that the foramen is usually rapid growth of the basal unit of the mandible (including
located around the border of the middle to the posterior third the MF) in comparison to the angular, coronoid, and articu-
of the ramus (0.28–0.40) within the sagittal plane lar units. The upper part of the basal unit therefore reached
(Table 15.3). The measurements using panoramic radio- an anomalous superior position. A similar case was pre-
graphs (0.36) yielded a higher value compared to anatomical sented by Holliday and Jackson (2011). The patient had an
measurements (0.32) (da Fontoura et al. 2002). unusual superior position of the mandibular foramen that
The effect of age on the anteroposterior (A-P) position of necessitated alternative routes of mandibular block.
the mandibular foramen (MF) was evaluated in 121 dry man- In a study evaluating the position of the mandibular foramen
dibles with primary (n = 36), mixed (n = 26), and permanent in 40 panoramic radiographs, the foramen was always situated
dentitions (n = 59) by Ashkenazi et al. (2011). The MF dis- in the anterior and inferior two-thirds of the ramus without dif-
tance from the posterior border of the ramus relative to the ference regarding side, sex, or age (Trost et al. 2010). In spite of
total ramus width in A-P dimension increased significantly the relative variability of the position of the mandibular fora-
(21.4 %) with altered dentitions from primary (0.28) to late men, it is unlikely to be located in the posterior and the superior
permanent dentition (0.34, p < 0.001). It was found that the one-third of the ramus. The authors considered the area to be
MF moved anteriorly with age and that this forward move- safe to perform vertical ramus osteotomies of the mandible with
ment of the MF was related to the growth process. a low risk of injury to the inferior alveolar nerve. Park et al.
An unusually high position of the MF within the ramus (2014) suggested using an artificial landmark, the midwaist
was documented bilaterally in a 54-year-old male by point, to locate the mandibular foramen. The midwaist point
Cvetko (2014). The panoramic radiograph showed that the was defined as the halfway point on a horizontal plane between
mandibular foramen was located in the upper quarter of the the most concave points on the anterior and posterior borders of
ramus height, and it was evident that a conventional man- the ramus. The mandibular foramen was most often located
dibular block would not be successful. A higher point of within 2 mm posterior to the midwaist point but displayed vari-
entry was chosen, but after 10 min no signs of anesthesia able positioning in the vertical plane.
Vertical Distance from the Mandibular 10 mm, whereas in children the foramen is often found
Foramen to the Occlusal Plane below the occlusal plane. However, the mandibular fora-
men may also be located below the occlusal plane in adults
Knowledge of the vertical distance between the occlusal (Afsar et al. 1998; Mbajiorgu 2000) (Figs. 15.8, and 15.9).
plane and the mandibular foramen is important for the Epars et al. (2013) demonstrated a positive correlation of
administration of the inferior alveolar nerve block. the vertical location of the MF and age assessed in 145 chil-
Some studies mentioned above provided data regarding dren between 6.3 and 14.6 years of age. They found that the
the location of the MF relative to the occlusal plane older the child, the higher the location. In older children the
(Table 15.4). In adults, the mean distance from the man- MF was located above and in younger children below the
dibular foramen to the occlusal plane ranges from 1.9 to occlusal plane.
Table 15.4 Distance (mm) from mandibular foramen (MF) to occlusal plane (OP)
Author(s) Study material N Distance
Hwang et al. (1990) 112 patients 112 (radiographic measurements) Children of 3 years: MF
(lateral cephalometric 4.12 mm below OP;
radiography) Children of 9 years: MF level
with OP;
Adults: MF 4.16 mm above OP
Afsar et al. (1998) 79 patients 79 (panoramic radiography) 1.9 ± 2.70
(radiographic (−9.0–11.0)
measurements)
(mean age 19.4 years)
70 (oblique cephalometric −0.1 ± 4.00
radiography) (−15.0–13.0)
(radiographic measurements)
(mean age 15.8 years)
Mbajiorgu (2000) 38 dry mandibles (adult black NA (anatomical measurements) In 29.4 % MF above OP
Zimbabweans) In 47.1 % MF level with OP
In 23.5 % MF below OP
Kanno et al. (2005)* 154 children 77 girls (panoramic radiography Age 7 years: 1.7 ± 2.70
(7–10 years) measurements) Age 8 years: 1.7 ± 1.91
Age 9 years: 2.9 ± 3.37
Age 10 years: 3.1 ± 2.77
77 boys (panoramic radiography Age 7 years: 0.5 ± 3.26
measurements) Age 8 years: 1.4a ±3.12
Age 9 years: 3.5a ±2.80
Age 10 years: 3.5 ± 3.35
a
Significant difference
Kositbowornchai et al. (2007) 23 partially dentate dry 33 (anatomical measurements) 10 (value mentioned in
mandibles (Thai) “discussion”)
Jalili (2010) 196 Iranian patients 49 females 3.5a ±0.69
(all measurements taken on right (panoramic radiography (2.2–5)
side) measurements)
(mean age 43.7 years) 52 males 3.7a ±0.61
(panoramic radiography (2.0–5.5)
a
measurements) Significant difference
Epars et al. (2013) 145 children 145 3.1 ± 2.6 mm
(mean age 10.4 years, range (lateral cephalometric radiography) (−3.1–9.6 mm)
6.3–14.6 years)
Kang et al. (2013) 49 patients (growth group) 98 3.2 ± 2.0 mm
(mean age 14.1 ± 2.9 years, range (CT with 3D reconstruction) (0.4–9.2 mm)
8–16 years)
59 patients (adult group) 118 3.8 ± 2.3 mm
(mean age 22.5 ± 1.9 years, range (CT with 3D reconstruction) (0.4–10.5 mm)
18–25 years)
*In this study, the distance to the occlusal plane was measured from the lingula and not from the mandibular foramen
316 15 Mandibular Foramen
MF
Spatial Relationship of Neurovascular patterns evident. Previous studies have found similar arrange-
Structures at the Foramen ments with the nerve located mostly anterior to the vessels
and the veins being the most laterally placed against the bony
A study evaluated the spatial arrangement of nerve and ves- surface of the ramus (Murphy and Grundy 1969; Barker and
sels within the neurovascular bundle at the level of the lingula Davies 1972; Roda and Blanton 1994). Hence, the inferior
in horizontal anatomical sections of 56 cadaveric hemisec- alveolar nerve was typically the most anterior structure within
tioned heads (Khoury et al. 2010). In 79 % of specimens, the the neurovascular bundle whereas the vasculature was more
inferior alveolar artery was found posterior or posterolateral posterior (Khoury et al. 2010). Anatomically, this arrange-
to the inferior alveolar nerve (Fig. 15.10). The inferior alveo- ment would appear the most likely since the inferior alveolar
lar veins (on average two veins, range 1–4 veins per speci- nerve takes origin from the mandibular division of the tri-
men) showed the same pattern with respect to the nerve. The geminal nerve anterior and superior to the inferior alveolar
position of the artery to the vein was very variable with no artery as the latter branches from the maxillary artery.
IAN
La
318 15 Mandibular Foramen
In the course of examining archaeological skeletal samples, The lingula (little tongue) is a bony projection on the medial
Ossenberg (1986) described an accessory opening above the aspect of the ramus located anteromedially to the mandibu-
mandibular foramen in a child’s mandible. An anomalous lar foramen (Fig. 15.11 and 15.12). It was first described by
canal 2 mm in diameter and 10 mm long crossed the base of Johannes-Baptist Spix (1781–1826, German biologist) in
the coronoid process and was termed the “temporal crest 1815 and termed “Spix’s ossicle or spine.” Occasionally,
canal” (TCC). A survey of retromolar variants in a large skel- the lingula can be palpated through the oral mucosa (Lipski
etal series revealed a TCC incidence of 1.7 %, ranging up to et al. 2013) and receives attachment of the sphenomandibu-
23 % in certain population samples (Ossenberg 1986). The lar ligament. Garg and Townsend (2001) dissected seven
accessory opening was consistently positioned on the medial cadaveric heads and reported that the appearance of the lin-
aspect of the ramus above the mandibular foramen (Chap. 17). gula did not seem to reflect the size of attachment of the
A relatively prominent unilateral accessory mandibular sphenomandibular ligament, suggesting an alternative
foramen was detected during routine scanning of dry man- explanation of lingula morphology, perhaps related to a
dibles by Das and Suri (2004). The foramen was located continuation of the mylohyoid ridge and anterior border of
4 mm superior to the mandibular foramen and 9 mm below the mylohyoid groove. In fact, Fabian (2006) showed that
the condylar notch. A 4-mm long bony groove extended in 64 % of 50 adult Tanzanian mandibles, the mylohyoid
from above to the accessory foramen. A radiograph taken groove originated from the medial wall of the MF at the
with a wire inserted into the accessory mandibular foramen posterior border of the lingula.
showed that the accessory mandibular foramen led to a canal Tuli et al. (2000) determined the shape of the lingula in
that terminated close to the root of the third molar. No com- 165 dry adult human mandibles (330 sides) from India. The
munication was visible with the mandibular canal. The shape was classified into four types: triangular (wide base
authors speculated that the two mandibular foramina leading and narrow-rounded or pointed apex), truncated (quadrangu-
to separate mandibular canals on the medial surface of the lar shape of bony projection), nodular (entire lingula except
mandible could have resulted during mesenchymal conden- apex merged into ramus), and assimilated (lingula com-
sation around the inferior alveolar nerve and vessels. pletely incorporated into ramus). The distribution of the
Presumably these two bony canals may have provided two shapes per sides was as follows: 68.5 % triangular, 15.8 %
separate channels, one for the inferior alveolar nerve and the truncated, 10.9 % nodular, and 4.8 % assimilated. In 95.2 %
other for the blood vessels (Das and Suri 2004). of the cases, the shape of the lingula was identical on both
Choi and Han (2014) assessed the CBCT data with regard to sides. Lingulae with free borders not attached to the ramus
the presence of double mandibular foramina. Eight double MF were observed in 11.5 %. Females (16.2 %) had more nodu-
were observed in six of 446 patients (1.35 %). All double MF lar types than males (9.6 %), but fewer truncated shapes
were located above the actual mandibular foramen on the medial (8.8 % versus 17.6 %). The apex of the triangular lingula was
aspect of the mandibular ramus. Accessory osseous canals orig- directed posterosuperiorly in 89.4 % of the cases, i.e., toward
inated from all double MF. In two cases, the accessory canal the condyle.
(forward type) entered the mandible through the double MF, ran A similar study assessed the shapes of the lingula in 73
forward, and terminated close to the roots of the mandibular dry Thai adult mandibles (Kositbowornchai et al. 2007).
molars. In six cases, the accessory canal (retromolar type) The most frequently encountered shape was the truncated
entered the mandible through the double MF, ran anteroinferi- lingula (47.2 %) with descending frequencies of the nodu-
orly, and terminated at a foramen in the retromolar fossa. lar (22.9 %), triangular (16.7 %), and assimilated types
The Lingula 319
CP
La
MF
Fig. 15.12 Superior view of the
left ramus in a dry mandible
displaying a pointed lingula. CP
coronoid process, La lingula, MF MHG
mandibular foramen, MHG
mylohyoid groove
320 15 Mandibular Foramen
CP
CM
CM
CP
ALa
ALa
EOL
Fig. 15.13 Lateral view of the right ramus in a dry mandible demon-
strating an antilingula. ALa antilingula, CM condyle of mandible, CP
coronoid process
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Mandibular Canal
16
The mandibular canal, also called inferior dental canal or d evelopmentally from three separate canals innervating dif-
inferior alveolar (nerve) canal, extends from the mandibular ferent tooth groups (Chavez-Lomeli et al. 1996) (Fig. 16.2).
foramen at the inner aspect of the ramus to the mental fora- The survey showed that a canal to the incisors appears first,
men along the mediolateral aspect of the mandible, thus tra- followed by a canal to the primary molars, and last by one or
versing the mandibular body (Fig. 16.1). The mandibular more canals to the first permanent molars. These separate
canal conveys the inferior alveolar nerve and the blood ves- canals are directed from the lingual surface of the mandibu-
sels of the same name and as such has gained considerable lar ramus toward the different tooth groups, and rapid prena-
attention in general dentistry as well as oral and maxillofa- tal growth and remodeling results in a gradual coalescence of
cial surgery. Various procedures such as root canal treatment; the canal entrances (Chavez-Lomeli et al. 1996). This theory
apical surgery; surgical removal of root fragments, teeth, would also explain the occurrence of bifid (duplicate or trip-
cysts, or tumors; insertion of dental implants; ridge augmen- licate) mandibular canals secondary to incomplete fusion of
tation and bone harvesting procedures; orthognathic man- the three separate canals.
dibular surgery; as well as placement of osteosynthesis The term mandibular canal implies the existence of an
devices may pose a risk to the inferior alveolar nerve and osseous tunnel containing a distinct nerve bundle enveloped
blood vessels. As a consequence, preoperative knowledge of by a perineurium; however, some authors have pointed to the
the location and course of the mandibular canal is essential to fact that branches of the inferior alveolar nerve bundle divide
avoid injuries to the neurovascular components of the man- within the medullary spaces of the mandibular body rather
dibular canal. than being present in a distinct tunnel (Denio et al. 1992).
A study evaluating 302 prenatal hemimandibles Thus, the term “nerve plexus” is often used to describe the
demonstrated that the mature mandibular canal arises
morphology of the nerve within the mandibular body.
a 0.76 mm deviation when evaluating the mandibular canal could not be detected in 11 of the 19 first molar areas and in
on CBCT images. two of the 19 second molar areas using CT while the man-
Additional radiographic modalities including MRI and dibular canal was identified in all 19 first and second molar
CT have also been investigated regarding the depiction and regions utilizing MRI resulting in a significant difference.
detection rate of the mandibular canal. Kamrun et al. (2013) Krasny et al. (2012) reported good visibility of the man-
compared cross-sectional CT images with panoramic radio- dibular canal in 69–72 % of the cases using axial and coro-
graphs. For both techniques, the superior border of the canal nal MR images, moderate visibility in 23–30 %, and not
showed significantly lower scores than the inferior border in visible in 1–8 % of the sample. In a study comparing MRI
all areas. The visibility of the superior border was very poor and CBCT for detection of the mandibular canal in
on panoramic radiographs, and the use of cross-sectional CT cross-
sectional images, investigators found significantly
images significantly improved the detection of the superior smaller observational variances and gave significantly
canal border (Kamran et al. 2013). Superiority of MRI over higher satisfactory scores when using MRI than CBCT
CT in detection of the mandibular canal was reported by (Chau 2012). The authors concluded that MRI should be
Imamura et al. (2004). Cross-sectional images of 19 first and considered if the mandibular canal cannot be identified
second molar sites in 11 patients were compared. The canal with CBCT.
Table 16.1 Radiographic visualization of mandibular canal (MC)
326
M3
MCup
periapical MC
lesion
MC
MClo
Fig. 16.5 Sagittal CBCT section of the left mandible showing good
Fig. 16.4 Right section of a panoramic radiograph in a 22-year-old
visibility of the mandibular canal in a 41-year-old female. MC man-
male with the upper border of the mandibular canal indistinguishable in
dibular canal
the molar region. MClo lower border of mandibular canal, MCup upper
border of mandibular canal, M3 right mandibular third molar
328 16 Mandibular Canal
MHR
MHR
SMF
SMF
MC
Fig. 16.8 The coronal CBCT image at the level of the second molar
lacks a typical trabecular pattern and thus the mandibular canal is not
Fig. 16.6 Coronal CBCT section (buccolingual plane) demonstrating
visible in this region. MHR mylohyoid ridge, SMF submandibular fossa
excellent visibility of the mandibular canal at the level of the second
molar since it is surrounded by dense bone. MC mandibular canal, MHR
mylohyoid ridge, SMF submandibular fossa
MC
periapical
lesion
MeF
periapical
lesion
MC
MC
buccal
lingual
MC
Fig. 16.9 Sagittal CBCT image of the right mandible showing excel-
lent visibility of the mandibular canal in a 61-year-old female. MC
mandibular canal
Course of Mandibular Canal The mean camber of the mandibular canal was highest for
the type 2 canals (9.7 ± 1.86 mm) and shortest for the type 1
Typically the mandibular canal courses from posterior to canals (6.9 ± 1.02 mm).
anterior and from lingual to buccal directions. Often the path The course of the mandibular canal was assessed in 52
of the canal demonstrates a curve in all three anatomical dry adult skulls from around the 1930s in eastern USA with
planes. Researchers have attempted to classify the course of all specimens dentate (skulls were excluded when a tooth
the mandibular canal. In a study using gross and microscopic was missing). Orthodontic wire was inserted into the canal
dissection of eight mandibles, Carter and Keen (1971) and CT scanning was performed (Ozturk et al. 2012). The
described three distinctive courses of the canal relative to the course of the mandibular canal showed a catenary-like con-
pattern of distribution of the inferior alveolar nerve (IAN) figuration (upward concave curve) in 51.1 % of cases, a pro-
and formulated morphological types (Figs. 16.11, 16.12, and gressive descent pattern (36.7 %), and a straight pattern
16.13): within the sagittal plane (12.2 %). In the buccolingual direc-
tion, the mandibular canal was found to be either in contact
Type I: The IAN was a single large structure lying in a bony with or in very close proximity to the molar lingual cortical
canal. The branches supplying the molar roots were very plate in the majority of cases. Nearing the mental foramen,
short and direct. the mandibular canal traveled to the buccal cortical plate and
Type II: The IAN was situated substantially lower down in showed three different emerging patterns at the mental fora-
the mandible at some distance from the molar roots. The men: a sharp turn (53.2 %), a soft curved exit (29.8 %), and a
dental branches branched off more posteriorly and were straight path (17 %) (Ozturk et al. 2012).
consequently longer and more oblique than in type I. With regard to the buccolingual location of the mandibu-
Type III: The IAN gave off a separate molar branch shortly lar canal, various pathways have been described within the
after entering the mandibular foramen, while the main body of the mandible (Figs. 16.14, 16.15, and 16.16). Denio
trunk of the IAN occupied a more inferior position and et al. (1992) studied sections of dry mandibles at locations
continued toward the mental foramen. defined by the apices of first and second premolars and
molars. The mandibular canal was often found buccal to the
Kieser et al. (2005) performed microdissection of the long axis of the distal root of the second molar and apical to
IAN in 107 cadaveric edentulous mandibles following buc- the mesial root of the second molar. In the area of the first
cal osteotomy to access the mandibular canal. The canal was molar, the canal was usually located lingual and then
located in the lower half of the mandible in 73 % of males changed its direction coursing inferior or buccal to the sec-
and in 70 % of females. The branching pattern of the nerve ond premolar. This anatomical pattern known as the
was classified into four morphological types: “S-shaped canal pathway” was the most commonly
observed (31 %) configuration. In 28 % of the hemimandi-
Type I: single unbranched nerve bles, the exact location of the canal could not be clearly
Type II: series of individual branches determined. In another 19 % it was located lingual, in 17 %
Type III: molar plexus buccal, and in 5 % directly inferior to the apices of the pos-
Type IV: proximal and distal plexus terior teeth (Denio et al. 1992). In a CT survey of 50
patients, the mandibular canal at the level of the first molar
The most common branching pattern was type II (59.6 % was located closer to the buccal surface in whites (4.6 mm)
in males and 52 % in females) followed by type III (21.1 % in compared to nonwhites (5.9 mm), and in the adjusted mul-
males and 26 % in females). The pattern of nerve distribution tiple regression model, age and race were statistically asso-
did not vary with its position within the mandible. In 25 ran- ciated with a buccal position of the canal (Levine et al.
domly selected mandibles, radiographs were taken before 2007).
dissection. None were classifiable as anything other than a Extracanalicular variations of the inferior nerve have been
single unbranched canal (Kieser et al. 2005). occasionally reported (Rusu et al. 2012). Following extreme
Liu and coworkers (2009) described four different courses vertical bone resorption, the inferior alveolar nerve may
of the mandibular canal following assessment of 100 pan- come to lie in a superficial groove of the mandible without a
oramic radiographs: bony roof, thus only covered by soft tissue (Fig. 16.17). Any
pressure to the soft tissue, for example, by dentures, will
Type 1: linear curve (approximate to straight line) cause severe pain. Further, mucosal incisions may sever the
Type 2: spoon-shape curve (similar to an asymmetric elliptic inferior alveolar artery causing profuse bleeding or may
arc) damage the nerve fascicles. An extracanalicular course of the
Type 3: elliptic arc curve (approximate symmetry) inferior alveolar nerve has also been described in a 20-year-
Type 4: turning curve (unsmooth curve with turning point) old fully dentate patient in conjunction with hemifacial
Course of Mandibular Canal 331
microsomia (Manikandhan et al. 2010). The ipsilateral man- course. The neurovascular bundle was then found outside
dibular canal and mental foramen were absent. The inferior along the lingual border of the mandible during intraoral
alveolar nerve entered the ramus on the medial aspect, but placement of a distraction device for mandibular lengthening
exited the ramus again laterally only after a short intraosseous (Manikandhan et al. 2010).
Fig. 16.13 IAN with distinct molar branch located above the
main trunk of the IAN (type III based on the classification by
Carter and Keen (1971))
332 16 Mandibular Canal
buccal
lingual
MeF MIC
buccal
MC
MC
lingual
MC
MC
Fig. 16.14 Axial CBCT scan showing a curved course of the mandibu-
lar canal in the body of the mandible in a 68-year-old female. MeF Fig. 16.15 Axial CBCT scan showing an oblique course of the man-
mental foramen, MC mandibular canal dibular canal in the body of the mandible in a 52-year-old male. MC
mandibular canal, MIC mandibular incisive canal
Course of Mandibular Canal 333
MC
buccal
lingual
MC
Fig. 16.16 Axial CBCT scan showing a straight course of the man-
dibular canal within the central part of the mandibular body in a
50-year-old female. MC mandibular canal
Size of Mandibular Canal Chen et al. (2013) reported that no significant difference was
observed for the diameter of the mandibular canal at the level
The diameter (width or height) of the mandibular canal has of the mental foramen when comparing males and females
been measured in several studies using different methodol- from both American (2.2 mm) and Taiwanese (2.1 mm) sub-
ogy. Mean measurements range from 2.1 to 4.9 mm jects based on CBCT images. An investigation assessing
(Table 16.2). It should be noted that the 4.9 mm value might cross-sectional CBCT images of 100 patients in the area of
be inflated since it was obtained in panoramic radiographs the first molar found a size <2 mm of the mandibular canal in
without taking the enlargement factor into consideration. only 8 % of the sample (de Oliveira et al. 2012).
Table 16.3 Distances (mm) from mandibular canal (MC) to adjacent root apices
Author(s) Study material N 2nd premolar 1st molar 2nd molar Comments
Littner et al. 42 dry mandibles 42 right sides – Mesial root: Mesial root: –
(1986) (radiographs) 5.5 ± 2.48 3.9 ± 2.13
Distal root: Distal root:
5.4 ± 2.31 3.5 ± 2.06
42 left sides – Mesial root: Mesial root: –
5.3 ± 2.11 4.1 ± 2.16
Distal root: Distal root:
5.4 ± 1.91 3.7 ± 1.94
(continued)
336 16 Mandibular Canal
Table 16.3 (continued)
Author(s) Study material N 2nd premolar 1st molar 2nd molar Comments
Denio et al. 22 dry mandibles 264 sections 4.8 ± 3.1 Mesial root: Mesial root: –
(1992) through roots 7.3 ± 3.4 5.3 ± 2.0
Distal root: Distal root:
7.2 ± 4.3 5.2 ± 2.3
Sato et al. 75 human Japanese 29–36 – Mesial root: Mesial root: –
(2005) cadaveric mandibles 10.6 ± 4.9 7.9 ± 4.4
(panoramic Distal root: Distal root:
radiography) 9.9. ±4.7 7.0 ± 4.5
Froum et al. 41 patients 135 teeth 4.9 ± 2.82 Mesial root: Distal root: –
(2011) (CT) (40 second 5.8 ± 3.07 4.4 ± 3.04
(age N/A) premolars, 47 first
molars, 48 second
molars)
Kovisto et al. 139 patients Age group I Males: Males: Males: Age group I
(2011) (CBCT) <18 years 1.8 Mesial root: Mesial root: Showed significantly
Females: 1.5 1.3 lower values than
1.7 Distal root: Distal root 1.2 groups II and III
1.4 Females:
Females: Mesial root:
Mesial root: 1.0
1.4 Distal root 0.6
Distal root 1.2
Age group II Males: Males: Males:
18–49 years 4.2 Mesial root: Mesial root:
Females: 4.3 2.6
2.9 Distal root: Distal root:
3.8 2.0
Females: Females:
Mesial root: Mesial root:
3.0 1.6
Distal root: Distal root:
3.0 1.4
Age group III Males: Males: Males: Significant
a, b
(2012) (CBCT) a
5.1 ± 1.6 differences
(age range 15–65 Distal root
years) b
4.8 ± 1.5
100 females – Mesial root –
a
4.4 ± 1.3
Distal root
b
4.1 ± 1.2
Lin et al. (2014) 237 patients 1008 teeth 6.1 ± 2.7 a
7.0 ± 2.9 4.3 ± 2.7
b
Significant
a,b
Table 16.4 Distances (mm) from mandibular canal (MC) to bone surfaces of the mandible
Upper (alveolar
Author(s) Study material N Buccal Lingual crest) Lower border Other Comments
Hwang et al. 15 fresh cadaveric heads 30 hemimandibles 2nd premolar: 2nd premolar: 2nd premolar: 2nd premolar: – –
(2005) (Koreans) 4.3 ± 1.3 4.2 ± 1.3 21.3 ± 2.8 9.4 ± 1.4
1st molar: 1st molar: 1st molar: 1st molar:
6.8 ± 1.5 2.8 ± 1.0 18.8 ± 2.6 9.1 ± 1.0
2nd molar: 2nd molar: 2nd molar: 2nd molar:
8.3 ± 1.7 2.4 ± 0.9 16.7 ± 2.3 10.0 ± 1.5
Sato et al. 75 human Japanese 29–36 – – – 1st molar – –
(2005) cadaveric mandibles Mesial root:
(panoramic 9.6 ± 2.6
radiography) 1st molar
Distal root:
9.4 ± 2.4
2nd molar
Mesial root:
9.8 ± 2.8
2nd molar
Distal root:
10.6 ± 3.0
Levine et al. 50 patients 50 1st molar: – 1st molar: – – At least 1st molar
(2007) (mean age 42.1 years) (one side per patient at 4.9 ± 1.3 17.4 ± 3.0 present
CT random) (1.3–7.8) (8.7–23.1)
de Oliveira 50 Brazilian patients 100 4.1 ± 1.53 5.8 ± 1.67 18.8 ± 2.74 10.5 ± 1.38 – Partially dentate
et al. (2011) (CT) section 1 (1–6 teeth in each
(mean age 100 6.4 ± 1.47 4.2 ± 1.56 16.1 ± 2.52 9.5 ± 2.15 hemimandible);
51.7 ± 4.5 years, range
section 2 Canal length was divided
25–75 years) 100 8.5 ± 1.82 3.8 ± 0.82 16.4 ± 2.65 10.4 ± 2.62 in 4 sections from distal
section 3 aspect of MF to region of
2nd molar
100 5.4 ± 1.44 2.1 ± 0.62 16.7 ± 3.41 11.8 ± 2.83
section 4
Kilic et al. 49 hemimandibles of 26 294 (measurements 4.6 ± 1.6 5.7 ± 1.6 14.1 ± 2.7 10.5 ± 1.5 – –
(2010) human cadavers taken at six cross
(dissection) sections)
Adigüzel et al. 200 patients 200 Mesial root 1st Mesial root 1st – – Width of Measurements at level of
(2012) (CBCT) molar: 5.2 ± 1.4 molar: 2.6 ± 1.7 mandible at MC first molar (M1)
(age range 15 - 65 Distal root 1st Distal root 1st level:
years) molar: 5.7 ± 1.5 molar: 2.1 ± 1.2 Mesial root M1:
10.7 ± 2.2
Distal root M1:
10.5 ± 2.1
16 Mandibular Canal
Chen et al. 200 patients 100 Americans – – – 9.8 ± 2.01 – Measurements at level of
(2013) (CBCT) (mean age mental foramen
53.3 ± 12.8 years, range
21–79 years)
100 Taiwanese – – – 10.1 ± 1.66 – Measurements at level of
(mean age mental foramen
53.7 ± 13.2 years, range
20–82 years)
Massey et al. 16 cadaveric 16 2nd premolar: 2nd premolar: 2nd premolar: 2nd premolar: – *Radiographic
(2013) hemimandibles (radiographic *4.3 ± 1.42 3.3 ± 1.64 11.7 ± 3.80 7.4 ± 2.15 measurement;
(micro-CT) measurements **4.7 ± 1.62 2.8 ± 1.28 13.0 ± 3.42 7.5 ± 1.90 **Anatomical
and 1st molar: 1st molar: 1st molar: 1st molar: measurement
caliper anatomical 6.1 ± 1.07 2.8 ± 1.35 11.8 ± 4.42 6.2 ± 1.82
measurements) 5.7 ± 1.13 2.5 ± 1.27 13.0 ± 4.42 6.6 ± 1.75
2nd molar: 2nd molar: 2nd molar: 2nd molar:
5.4 ± 1.20 2.8 ± 1.29 13.8 ± 4.37 7.5 ± 1.57
Distances from Mandibular Canal to Bone Surfaces
Components of Mandibular Canal removed to trace the finer nerve branches to the tooth apices
and periodontal areas. The dissection revealed that soon after
The mandibular canal houses the IAN, the inferior alveolar entering the canal, a molar branch left the IAN to reach the
artery (IAA) and vein (s), autonomic nerve fibers traveling apices of the molars and, in some instances, the second pre-
with the artery, and lymphatic vessels (Figs. 16.19 and 16.20). molar. The main trunk divided into two distinct branches in
The IAN arises from the posterior trunk of the mandibular the molar region, the mental and incisive branches, the latter
division of the trigeminal nerve (CN V3), and it courses medial supplying the canine and incisor teeth. A recurrent branch
to the lateral pterygoid muscle and posterolateral to the lingual from the mental nerve was consistently found to reenter the
nerve. As the IAN approaches the attachment of the spheno- mandible to supply fibers to the area surrounding the canine
mandibular ligament to the lingula, it dives inferolaterally as a and first premolar. The fibers supplying the premolars were
single trunk through the mandibular foramen into the man- inconsistent in their origin. The premolars were either inner-
dibular canal, but then quickly arborizes forming a neurovas- vated by a plexus of fibers or by distinct separate fibers from
cular plexus along with the inferior alveolar artery and vein the main trunk. Unlike the obliquely oriented fibers supply-
(Zoud and Doran 1993). Just prior to entering the canal, it ing the molar teeth, those supplying premolars, canines, and
receives collaterals from the lingual and auriculotemporal incisors emerged perpendicular to the common trunk (Wadu
nerves (Racz et al. 1981; Zoud and Doran 1993). It then joins et al. 1997).
with the inferior alveolar artery and vein to create a neurovas- Pogrel et al. (2009) studied the anatomic structure of the
cular bundle (Gowgiel 1992; Zoud and Doran 1993). The inferior alveolar neurovascular bundle in eight cadaveric
nerve supplies the mandibular teeth and forms the mental hemimandibles. The buccal plate was removed from the
nerve as a terminal branch (Starkie and Steward 1931). mandibular angle and body region, and the contents of the
The inferior alveolar nerve conducts general somatic mandibular canal were carefully identified and dissected. In
afferent modality while also serving as a conduit for post- all cases, the vein was positioned superior to the nerve, while
ganglionic sympathetic fibers that arise from the superior the artery was located lingual to the nerve. Histologically,
cervical ganglion and distribute via the external carotid the macroscopic relationship was confirmed, and the artery
artery from the superior cervical ganglion to the dental pulps appeared as a single vessel, whereas usually multiple veins
of the mandibular teeth (Racz et al. 1981). Parasympathetic (3–5) were present. The authors also reported that this
innervation remains contested, but physiological evidence arrangement was observed clinically in a patient on which
from experimental animal models suggests that fibers may marginal mandibular resection was performed therapeuti-
distribute from CN VII running with V to the pulp with some cally (Pogrel et al. 2009).
dilatory effect (Olgart 1996). Hur et al. (2013) studied the microarchitecture of the
The IAA arises as a branch from the maxillary artery and components within the mandibular canal in 30 hemifaces
distributes to the apical foramina of the roots communicating following injection of Latex and coloring agent into the com-
with the capillary plexus that drain, in turn, through the infe- mon carotid arteries. Of these, 17 hemimandibles were
rior alveolar vein. The vascular pattern appears to be very decalcified and subsequently microdissected with the aid of
constant in expression within the canal, but the IAA can vary a surgical microscope, while 13 specimens were scanned
with respect to its origin arising directly from the external using a micro-CT system. The most common spatial organi-
carotid artery (Jergenson et al. 2005). zation of the IAN fascicles could be grossly classified as fol-
Lymphatic drainage of the mandible traditionally was lows: a superior buccal portion innervating the molars, a
considered to occur along periosteal systems that drain exter- superior portion innervating the premolars, a lingual portion
nally through the submandibular lymph nodes. However, innervating the canines and incisors, and a buccal portion
Yaghmaei et al. (2011) performed immunohistochemical that included two-thirds of the inferior alveolar nerve and
analysis utilizing lymphatic-specific markers and showed terminated as the mental nerve (Hur et al. 2013). Such a dis-
that small channels course within interfascicular areas among tinctive fascicular organization of the IAN could make it
and between the MC neurovascular bundles without signifi- possible to forecast the degree, location, and extent of nerve
cant differences in pattern bilaterally or along the anteropos- damage according to presenting symptoms. The description
terior axis of the canal. These interfascicular lymphatics correlates with the report on prenatal nerve paths of the IAN
could provide a route for lymphocytic infiltration of the by Chavez-Lomeli (1996), as mentioned earlier. The authors
nerve leading to widening of the MC when viewed with pan- described also three types of relationships between the IAN
oramic radiography (Vartiainen et al. 2008). and the IAA within the mandibular canal. Most frequently
A detailed analysis of the IAN was performed in nine the artery was located superior and lingual to the nerve
human cadaveric mandibles by Wadu et al. (1997). Following within the canal and would therefore be more vulnerable to
demineralization and dissection from the lingual aspect of instrument-induced damage than the nerve. In all specimens,
the mandible, bony trabeculae along the IAN were carefully one arterial branch separated from the IAA immediately
Components of Mandibular Canal 341
after entering the mandibular foramen typically supplying into two branches. One nerve was identified as the incisive
the mandibular molars (Hur et al. 2013). mandibular dental nerve and the other as the mental nerve.
Ikeda et al. (1996) measured the components within the Histologically, the incisive mandibular dental nerve com-
mandibular canal using MRI and sections obtained with a prised 3–4 nerve fascicles, whereas the mental nerve dis-
cryomicrotome. The mean diameter of the IAN was played a single large nerve bundle. Both nerves were finely
2.2 ± 0.4 mm and of the IAA 0.7 ± 0.2 mm. Near the man- wrapped with epineurium.
dibular foramen, the artery was located inferior to the nerve Bertl et al. (2015) assessed the position of the IAA within
(in 50 % inferolateral and in 50 % inferomedial). In the mid- the mandibular canal in 15 heads of fresh human cadavers.
dle section of the canal, the artery was located in the supero- Following injection of iodine contrast medium in both exter-
medial portion of the canal. The IAN contained 2–8 fascicles, nal carotid arteries, CT scans were reformatted and evalu-
underscoring the utility of MRI for selecting a donor nerve ated. The main IAA changed its position within the
with fascicular size and patterns consistent with the host mandibular canal on average 4.3 times, but with a similar
nerve. bilateral course. The IAA was most frequently positioned in
A study utilizing 10 human cadaveric mandibles assessed the cranial portion of the mandibular canal (42 %), followed
morphological features of the IAN by comparing bilateral by a lingual (36 %), caudal (16 %), and buccal (6 %) location
observations obtained using macroscopic dissection and his- within the canal. At the mandibular foramen, the IAA had
tological examination (Kqiku et al. 2011). The IAN com- most often a caudal position, whereas in the body segment of
prised two distinct larger nerves that were separately wrapped the mandible, the cranial and lingual positions prevailed. The
in perineural sheaths and spirally arranged around each rare buccal location was limited to the ramus area of the
other. Macroscopically, the IAN divided in the molar area canal (Bertl et al. 2015).
IAA
IAN IAA
MeN
IAN
342 16 Mandibular Canal
IAN
MeF
Bifid Mandibular Canal Type I: retromolar canal (reaches foramen on bone surface in
retromolar region)
The mandibular canal is usually, but not invariably, single Type II: dental canal (reaching apices of second and third
and bilaterally symmetrical. The term “bifid” mandibular molars)
canal refers to dual or double canals within the mandibular Type III: forward canal (with/without confluence to the main
body (Figs. 16.21, 16.22, 16.23, 16.24, and 16.25). Though mandibular canal)
studies using panoramic radiography have shown low fre- Type IV: buccolingual canal (arising from the buccal or lin-
quencies of bifid mandibular canals (< 10 %), these have gual wall of the mandibular canal)
been documented recently with CBCT imaging to be present
in up to 66.7 % of patients and up to 46.5 % of sides The vast majority (112/114) of morphological types I–III
(Table 16.5). originated from the superior wall, while one type IV case
Distinctive varieties of supplemental canals large enough arose from the buccal wall and another type IV pattern was
to be seen on panoramic radiographs have been described in seen arising from the lingual wall. The most frequent type of
detail by Nortje et al. (1977). They suggested the following bifid mandibular canal was the forward canal without conflu-
classification (Fig. 16.26): ence (55.3 %). In a subsequent study, the authors compared
CBCT and multislice CT and found no significant difference
Type I: two canals originating from one foramen in the detection of bifid mandibular canals comparing the
Type II: a short supplemental upper canal extending to the two modalities (Naitoh et al. 2010).
second or third molar Numerous variations of bifid mandibular canals have
Type III: two mandibular canals of equal dimension appar- been reported in the literature. Claeys and Wackens (2005)
ently arising from two separate foramina in the ramus and described a 19-year-old patient who presented a bifid man-
joining together in the molar region to form one canal dibular canal on the right side in the panoramic radiograph.
Type IV: a supplemental canal arising in the retromolar pad Cross-sectional CT images demonstrated a duplicated canal
region and joining with the main canal in the retromolar originating from two separate mandibular foramina. The
area lower canal ran to the mental foramen, whereas the upper
canal coursed lingually to exit through a lingual foramen
After CBCT evaluation of 114 bifid mandibular canals in mesial to the second premolar. In the three other radio-
79 out of 122 patients, Naitoh et al. (2009) suggested the fol- graphic case reports with bifid mandibular canals, two
lowing classification (Fig. 16.27): cases each had a separate buccal foramen as the anterior
Bifid Mandibular Canal 343
opening of the bifid mandibular canal (Rouas et al. 2007). sory canals with a narrow diameter and those that bifurcate
In one of the two case reports by Mizbah et al. (2012) in any direction (Kuribayashi et al. 2010).
describing bifid mandibular patterns, the upper canal ran Orhan et al. (2011) measured the length of bifid canals in
lingually to the roots of the third molar and thus was highly CBCT images of 242 patients (484 sides). The longest mean
susceptible to injury during s urgical removal of the third length was calculated for the forward type of bifid canal with
molar. In the other case, a trifid mandibular canal was docu- 20.1 mm compared to 8.3 mm for dental canals and 3.8 mm for
mented with the third canal actually being a retromolar buccolingual canals. No statistically significant differences
canal. A similar case was documented by Auluck et al. were found between left and right sides, and males and females.
(2005) who presented three mandibular canals in the areas In contrast, significantly longer bifid canals were measured in
of the left ramus and the mandibular angle. The appearance males (11.5 ± 5.7 mm) than in females (8.2 ± 2.4 mm) in a CT
of bifid or trifid mandibular canals appears to be correlated study including 173 patients (Fu et al. 2014). The same authors
with the prenatal morphogenesis of the mandibular canal also reported that mandibles had larger cross-sectional bone
originating from three separate canals innervating different areas when bifid canals were present. Shen et al. (2014)
tooth groups and incomplete fusion of the distinct canals assessed the course and location of 170 bifid canals found in
(Chavez-Lomeli 1996). 616 hemimandibles using CBCT or multislice CT. Among the
When examining panoramic radiographs, caution must be bifid canals, 95.9 % were located superior to the main mandib-
used to avoid misinterpreting contiguous anatomical struc- ular canal, and the same percentage of bifid canals exhibited a
tures such as the mylohyoid groove, the mylohyoid crest forward course. A frequency of 91.1 % of bifid canals did not
(internal oblique ridge), and other radiologic osteosclerotic rejoin the main mandibular canal. Bifid canals were predomi-
areas or radiolucencies such as bifid mandibular canals nantly located in the retromolar (40 %), ramus (27.7 %), and
(Sanchis et al. 2003). In contrast, CBCT provides high- molar areas (17.1 %). The remaining bifid canals were found in
resolution three-dimensional images that can detect acces- the premolar area (11.8 %) or near the mental foramen (3.5 %).
M1
BiMC
periapical
lesion
MC
MC
M2
M3
BiMC
M3
M3
BiMC
M3
MC
BiMC
MC
MC
MC
lesion
MC
MeF
M3
BiMC
MC
buccal lingual
Table 16.5 (continued)
Author(s) Study material N Incidence of BMC Types Comments
Kuczynski et al. 3024 patients (panoramic – 1.98 % (patients) 83.3 % (Langlais I), –
(2014) radiography) (mean age 30 16.7 % (Langlais
years) II),
0 % (Langlais III or
IV)
Murat et al. (2014) 225 patients 450 sides 36.8 % (patients) N = 111 Mean diameters:
(CBCT) 22.8 % (sides) 38.7 % forward Forward canal:
(mean age 43.9 years, range canal 1.5 ± 0.4 mm
13–79 years) 36.0 % retromolar Retromolar canal:
canal 1.6 ± 0.7 mm
17.1 % dental canal Dental canal:
5.4 % buccolingual 2.0 ± 1.1 mm
canal Buccolingual canal:
2.7 % superior canal 1.5 ± 0.7 mm
Superior canal:
0.7 ± 0.2 mm
Neves et al. (2014) 127 patients (CBCT and 254 sides 7.4 % (panoramic Based on CBCT, –
panoramic radiography) radiography) 80 % of bifid
(mean age: 41.9 years, 9.8 % (CBCT) mandibular canals
range 18–61 years) were located
posterior to the
lower third molar
and 20 % on the
mandibular body
Shen et al. (2014) 308 Taiwanese patients 616 sides 41.2 % (patients) – Location of bifid
(CBCT or multislice CT) 27.6 % (sides) canals:
(mean age 51 years, range 27.7 % ramus area
12–85 years) 40.0 % retromolar
area
17.1 % molar area
11.8 % premolar
area
3.5 % mental
foramen area
348 16 Mandibular Canal
Fig. 16.26 Illustration of the classification of bifid mandibular canals based on Nortje et al. (1977)
Bifid Mandibular Canal 349
Fig. 16.27 Illustration of the classification of bifid mandibular canals based on Naitoh et al. (2009)
350 16 Mandibular Canal
Mandibular Canal and Third Molars 1. Darkening of the root where it crosses the mandibular
canal
The intimate relationship of the roots of the third molar 2. Bifid root apex representing intimacy of the apical peri-
with the mandibular canal as well as its crown when the odontal membrane
tooth is deeply impacted place the IAN and IAA at a high 3. Narrowing of the root implying perforation or grooving
risk of injury during surgical extractions (Figs. 16.28, by the mandibular canal
16.29, 16.30, 16.31, 16.32, 16.33, 16.34, 16.35, 16.36, 4. Deflected or hooked roots around the mandibular canal
16.37, 16.38, 16.39, 16.40, 16.41, 16.42, 16.43, 16.44, 5. Diversion or bending of the mandibular canal in the
16.45, 16.46, 16.47, and 16.48). Weighing the risks of region of the root apices
prophylactic tooth removal against complications when 6. Narrowing of the mandibular canal
leaving the third molar in place remains a highly debated 7. Interruption or obliteration of either of the radiopaque
topic in dentistry as well as in oral surgery. It is beyond white (cortical) lines of the mandibular canal
the scope of this anatomical textbook to address the ques-
tion, and the reader is encouraged to consult the pertinent Friedland et al. (2008) added two other signs to this list
literature. However, we will focus on anatomical perspec- including (I) superimposition of third molar root to mandibu-
tives and risks of surgical removal of the mandibular third lar canal and (II) direct contact of root with superior border
molar related to the mandibular canal. Other anatomical of mandibular canal.
aspects such as damage to the lingual nerve, perforation Using panoramic radiography, Rood and Shehab (1990)
of the submandibular fossa, and tooth displacement into reported that three (#1, 5, and 7 in list above) of the seven
adjacent anatomical spaces are discussed in the corre- classic radiographic signs indicated a higher risk of IAN
sponding chapters. injury, implicating close proximity of IAN to the lower third
Among 149 evaluated cases with postsurgical IAN molar. In a case-control study, Blaeser et al. (2003) identified
impairment, third molar removal was the predominant cause the same factors (#1, 5, and 7) as predictive of IAN injury. In
(63.1 %). Implant surgery (10.7 %), mandibular block anes- a larger case-control study by Kim et al. (2012), the follow-
thesia (10.1 %), dentoalveolar surgery (7.4 %), endodontic ing factors were found to be significantly associated with
treatment (6.7 %), and unknown (2.0 %) were the other rea- IAN deficits: older age, deep impaction, darkening, deflec-
sons (Hillerup 2007). tion, or narrowing of roots, bifid apices of roots, as well as
According to a recent literature review, the risk of IAN narrowing of the mandibular canal.
deficits after third molar surgery ranges between 0.26 and It has been shown that panoramic radiography does not
8.4 % (Leung and Cheung 2011). The authors identified the provide sufficiently reliable images to predict nerve lesions
following significant risk factors: increased age, unerupted (Hasegawa et al. 2013). As a consequence, three-dimen-
tooth, deep impaction, specific radiographic signs, intraop- sional imaging (CT, CBCT) is recommended when pan-
erative exposure of the IAN, and lingual split technique. In a oramic radiographs point to a close relationship between the
large prospective study involving 3236 patients who under- mandibular canal and the third molar (Friedland et al. 2008;
went surgical removal of impacted mandibular third molars, Eyrich et al. 2011; Lübbers et al. 2011; Hasegawa et al.
significant risk factors for IAN deficits included the patient’s 2013). In contrast, Ghaeminia et al. (2009) found no superi-
age (26–30 years), horizontal tooth impaction, close radio- ority of CBCT versus panoramic radiography in a prospec-
graphic proximity of mandibular canal, and treatment by tive study of consecutive patients comparing both
trainee surgeons (Jerjes et al. 2010). radiographic modalities in predicting exposure of the
A study comprising 3595 patients with removal of IAN. However, the authors emphasized that CBCT is well
4338 lower third molars found that the only significant suited to elucidate the 3D relationship between the tooth and
factor related to the risk of IAN damage was depth of the mandibular canal. Similarly, Guerrero et al. (2014)
tooth impaction (Cheung et al. 2010). In a 4-year study reported that CBCT was not better than panoramic radiogra-
assessing clinical incidents in conjunction with removal phy in predicting postoperative complications for moderate-
of 11,599 lower third molars in 6803 patients, the inci- risk cases of impacted third mandibular molars. Nonetheless,
dences of temporary and permanent IAN injuries were CBCT images can accurately confirm the number of roots
0.44 % and 0.24 %, respectively (Nguyen et al. 2014). and root morphology of the third molar compared to pan-
Important risk factors included increasing age (≥ 25 oramic radiography.
years), surgery performed under general anesthesia, and Harada et al. (2013) assessed the correlation of radio-
mesioangular impactions. graphic signs on panoramic radiographs and anatomic
Radiologic signs suggesting an intimate, anatomical rela- features of thinning of the cortical plates and closeness of
tionship between third molars and the mandibular canal the root of the third molar to the mandibular canal on
include (Rood and Shehab 1990; Blaeser et al. 2003; Kim CBCT images. Darkening of the root and interruption of
et al. 2012) (Fig. 16.49): the white (cortical) line of the mandibular canal in pan-
Mandibular Canal and Third Molars 351
oramic radiographs were found to predict lingual cortical associations. Recent CT studies reported that cases with
plate thinning and close proximity between the third absence of cortication of the mandibular canal and a
molar root and the mandibular canal. In a similar study, dumbbell-shaped canal present a high risk of IAN injury
Shahidi et al. (2013) assessed panoramic radiography during third molar removal (Ueda et al. 2012; Shiratori
signs validated with CBCT scans to predict proximity of et al. 2013).
the third molar roots to the mandibular canal. Loss of cor- The location of the mandibular canal relative to the third
tical line (odds ratio, OR 5.75), root dilaceration (OR molar roots as detected with 3D imaging is summarized in
5.28), and root darkening (OR 4.92) yielded the highest Table 16.6.
MC
M2
M3
MC
M2
M3
M2
M3
MC
lingual
buccal
MC
MC
Fig. 16.32 Sagittal CBCT image of the right mandible showing the
mandibular canal projected over the roots of the impacted third molar in
a 23-year-old female. MC mandibular canal, M2 mandibular second
molar, M3 mandibular third molar
Fig. 16.30 The coronal CBCT section demonstrates that the mandibu-
lar canal courses along the lingual aspect of the third molar. MC man-
dibular canal, M2 mandibular second molar, M3 mandibular third molar
M3
MC
buccal buccal
lingual
lingual MC
MC
Fig. 16.31 The axial CBCT image (inferior view) shows the narrow- Fig. 16.33 The coronal CBCT image confirms that the mandibular
ing of the mandibular canal on the lingual aspect of the roots of the third canal courses between the buccal and lingual roots of the impacted third
molar. MC mandibular canal molar. MC mandibular canal, M3 mandibular third molar
Mandibular Canal and Third Molars 353
M3al
NVB
M3al
buccal lingual
M3
lingual
buccal
MC
MC
Fig. 16.37 The mandibular canal also projects onto the roots of the
third molar as demonstrated in the sagittal CBCT image. MC mandibu-
lar canal, M2 mandibular second molar, M3 mandibular third molar
Mandibular Canal and Third Molars 355
anterior
MC
lingual
buccal root
root of M3
of M3
MC
Fig. 16.40 The patient declined complete extraction of the third molar
to avoid neurosensory disturbances of the inferior alveolar nerve. The
postsurgical panoramic radiograph shows the situation after coronec-
tomy of the right mandibular third molar
posterior
Fig. 16.39 The axial CBCT view demonstrates that the mandibular
canal passes between the buccal and lingual root portions of the third
molar. MC mandibular canal, M3 mandibular third molar
356 16 Mandibular Canal
lingual buccal
MC
MC
MC
buccal
MC lingual
MC
Fig. 16.42 The sagittal CBCT section demonstrates the course of the
mandibular canal at the level of the cementoenamel junction (note that
the crown is affected by replacement resorption). MC mandibular canal
Fig. 16.44 The axial CBCT view demonstrates the intimate relation-
ship between the mandibular canal and the roots of the third molar. MC
mandibular canal
Mandibular Canal and Third Molars 357
M3
CEJ
buccal
MC
lingual
Fig. 16.47 The coronal CBCT (buccolingual view) exhibits that the
mandibular canal is located buccal to the third molar close to the level
of the cementoenamel junction (a cystic radiolucency can also be seen
MC on the buccal aspect of the crown of the third molar). CEJ cementoe-
namel junction, MC mandibular canal, M3 mandibular third molar
M3
MC
MC
lingual
buccal
MC
Fig. 16.46 The sagittal CBCT (mesiodistal view) of the lower left
molar region demonstrates the proximity (double arrow) of the man-
dibular canal to the retromolar bone crest. MC mandibular canal, M3
mandibular third molar
Fig. 16.48 The axial CBCT exhibits the course of the mandibular
canal buccal to the two roots of the third molar. MC mandibular canal
358 16 Mandibular Canal
a b c d
e f g
Fig. 16.49 Illustration of radiographic signs indicating a close rela- root apices, (c) narrowing of root apices, (d) deflection of root apices,
tionship of the roots of the mandibular third molar and the mandibular (e) bending of mandibular canal, (f) narrowing of mandibular canal, (g)
canal (based on Kim et al. 2012). (a) Darkening of root apices, (b) bifid interruption of superior border of mandibular canal
Mandibular Canal and Third Molars 359
Table 16.6 Location of the mandibular canal (MC) relative to the roots of mandibular third molars
Inter- Intra-
Buccal Inferior Lingual radicular radicular
Authors Study material N location location location location location Comments
Khan et al. 48 patients 93 teeth 30.4 % 21.7 % 43.5 % – – In 4.3 % bifid
(2011) (CT) course of MC
(age range 19–50
years)
Lübbers et al. 472 patients 707 teeth 52.8 % – 37.3 % 8.2 % 1.7 % In 69.7 % direct
(2011) (CT) contact of tooth
(age NA) with MC
In 45.1 % with
narrowing of
MC
Yamada et al. 96 patients 112 teeth 40.2 % 36.6 % 23.2 % – – In 57.5 % direct
(2011) (CBCT) contact of tooth
(age range 16–77 with MC
years)
Neves et al. 33 patients 63 teeth 12.7 % 15.9 % 34.9 % 36.5 % – –
(2012) (CT)
(mean age
26.4 years, range
16–55 years)
Harada et al. 307 patients 290 teeth 27.2 % 41.7 % 23.4 % 7.6 % – –
(2013) (CBCT)
(mean age
36.4 years, range
19–82 years)
Shiratori et al. 115 patients 169 teeth 46.7 % 31.4 %* 21.3 % 0.6 % – *In 6 cases with
(2013) (CT) inferior location,
(mean age the MC coursed
32.5 years, range from buccal to
18–71 years) lingual in 3
cases and from
lingual to buccal
in 3 cases
Schneider et al. 699 patients 1197 teeth 29.0 % 39.2 % 23.8 % 7.4 % 0.6 % –
(2014) (CBCT)
(mean age
28.4 ± 12.1 years,
range 8–89 years)
360 16 Mandibular Canal
Mandibular Canal and Dental Implants imaging when conventional radiography has failed to dem-
onstrate relevant anatomical boundaries (Harris et al. 2012).
One of the more serious complications of dental implantology Givol et al. (2013) evaluated 92 cases with neurosensory
is injury to the IAN with altered sensation and/or persistent deficiency related to dental implants that resulted in liability
pain following placement of dental implants in the posterior claims. In most cases (76 %) treatment planning was based
mandible (Figs. 16.50, 16.51, 16.52, 16.53, and 16.54). The on conventional radiography. However, preoperative CT and
prevalence of such a complication has been reported as high as short dental implants were not a guarantee for avoiding IAN
13 % (Bartling et al. 1999; Alhassani and AlGhamdi 2010). injury. In a split-side cadaver study, CBCT-based implant
Causes of sensitivity alteration include damage to the IAN by drills violated the IAN (4.5 %) significantly less compared to
the implant drill or pressure/compression by the implant body treatment planning with periapical radiography (31.8 %), and
(Park et al. 2012). Hemorrhage or bone infracture may also the authors recommended CBCT as the principal imaging
impinge on the IAN (Juodzbalys et al. 2013). In the posterior modality for pre-implant assessment of the posterior mandi-
mandible with large spongy compartments or in cases with ble (Murat et al. 2014).
immediate implant placement following tooth extraction, the Park et al. (2012) described two cases with paresthesia
IAN is also at risk when the clinician attempts to achieve pri- following implant placement without radiographic evidence
mary implant stability in more apical areas. The additional of direct injury to the IAN. Corticosteroid medication was
hazard of damaging bifid mandibular canals in potential posi- prescribed for several weeks but the symptoms persisted.
tions of dental implant placement has been rarely addressed After removal of the implants, the paresthesia disappeared.
(Shen et al. 2014). In the region of the mental foramen (Chap. The authors concluded that if the IAN courses close to the
18), flap elevation, mental nerve compression by retraction dental implant and is not protected by the roof of the canal,
instruments, and periosteal release incisions may also cause compression of the cancellous bone by the implant is
postsurgical sensitivity changes. transmitted to the nerve resulting in paresthesia.
Proper treatment planning including three-dimensional Decompression by removing the implant appears the only
radiography is one of the most important steps to avoid way to relieve the symptoms (Park et al. 2012). In another
neural complications in dental implantology. The recently case report, an implant was found to compress an accessory
published EAO guidelines for the use of diagnostic i maging (bifid) mandibular canal above the main canal. Symptoms
in implant dentistry recommend to apply cross-sectional resided after implant removal (Maqbool et al. 2013).
M2
iM1
iM1
MeF
MC
Fig. 16.51 The sagittal CBCT image demonstrates that the implant in
the first molar site projects over the mandibular canal. iM1 implant
in location of first molar, MC mandibular canal
Mandibular Canal and Dental Implants 361
Fig. 16.54 The area of the sensory loss in the lower left jaw due to
surgical damage during implant bed preparation/implant insertion to
Fig. 16.53 The removed implant the inferior alveolar nerve
362 16 Mandibular Canal
Mandibular Canal and Endodontic Treatment (Fanibunda et al. 1998; Poveda et al. 2006; Gonzalez et al.
2010) (Figs. 16.55, 16.56, 16.57, 16.58, 16.59, 16.60, and
Conventional root canal treatment in the posterior mandible 16.61). A rare incidence is the displacement of a separated
has been associated with the possibility of IAN damage endodontic instrument into the mandibular canal (Gandhi
(Mohammadi 2010). Retrospective analyses of patients et al. 2011). Pogrel (2007) retrospectively reviewed 61
referred with IAN impairment demonstrated an endodontic cases with damage to the IAN after root canal therapy. He
cause between 2.1 % and 6.7 % of cases (Hillerup 2007; suggested that early surgical exploration and debridement
Tay and Zuniga 2007). Main causes of endodontic IAN might reverse the side effects (pressure, neurotoxicity) of
damage include mechanical nerve injury by over-instru- endodontic agents on the IAN.
mentation, excessive preparation with disruption of the api- A serious complication of endodontic treatment is the
cal constriction resulting in extrusion of irrigants, inadvertent injection of calcium hydroxide paste into the infe-
medicaments and obturation materials (chemical, thermal, rior alveolar artery with subsequent retrograde intravascular
and/or mechanical damage), and extrusion of debris and displacement, tissue necrosis, and chronic pain (Lindgren
bacteria from the root canal as a result of infectious damage et al. 2002; Sharma et al. 2008; Wilbrand et al. 2011).
M3
BiMC
MC
MC
MeF
Fig. 16.55 Sagittal CBCT image of the mandible of a 62-year-old dibular canal and caused severe pain and paresthesia. MC mandibular
male demonstrating that calcium hydroxide paste (arrowheads) was canal, MeF mental foramen, M3 third molar, BiMC bifid mandibular
overfilled in the bifid mandibular canal during root canal treatment of a canal
mandibular right third molar. The material ascended into the main man-
Mandibular Canal and Endodontic Treatment 363
M3 M3
BiMC
MC
MC
BiMC
MC
Fig. 16.56 Sagittal CBCT detailed image confirms that the calcium
hydroxide material is located within the bifid mandibular canal superior
to the main mandibular canal. MC mandibular canal, M3 third molar,
BiMC bifid mandibular canal (with white material calcium hydroxide)
Fig. 16.58 Extraoral view exhibiting the area of the neurosensory dis-
turbances (paresthesia, hyperesthesia) in the region of the right lower
lip, chin, and anterior cheek Fig. 16.59 Sagittal CBCT image of right mandibular second molar
showing root canal filling material extending into the mandibular canal
in a 21-year-old male
364 16 Mandibular Canal
Fig. 16.60 The axial CBCT view confirms that the foreign material
extruded into the mandibular canal
a b
MeF
MIC MC
MC
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Retromolar Canal
17
Löfgren (1957) was the first to describe the retromolar that arose from cross-marriage of Europeans and Argentine
foramen after studying mandibles from Nordic graveyards. aborigines.”
The first detailed analysis about the retromolar canal was With three-dimensional radiography becoming more pop-
published by Schejtman et al. in 1967. They evaluated the ular and more available, the interest in the retromolar canal
nature of the content of the mandibular retromolar canal as has augmented considerably, detailing its origin, course, and
well as the origin and fate of its elements in 18 human dimensions. The retromolar canal normally arises from the
heads from Argentina preserved in formaldehyde. They mandibular canal posterior to the third molar or, if the wis-
reported a canal in 13 of the heads (72 %), in five of which dom tooth is absent, distal to the second molar (Figs. 17.1
(27 %) it was bilateral. They further wrote: “The retromolar and 17.2). The canal passes upward to the retromolar fora-
canal originates from the inferior dental canal and, after men located in the retromolar fossa (von Arx et al. 2011a)
describing a recurrent path, it ends either in the retromolar (Fig. 17.3). Occasionally, a soft tissue bundle is seen emerg-
foramen or in surrounding foramina. The elements occupy- ing from the bone surface distal to the third molar after flap
ing it are derived from their inferior dental homologues. elevation for mandibular wisdom tooth removal (Figs. 17.4
The most frequently found components, in decreasing and 17.5). Histology has demonstrated that the retromolar
order, were a myelinated nerve, one or more arterioles and canal contains a neurovascular structure, yet the clinical sig-
one or more venules. After leaving the body of the mandi- nificance remains unclear (von Arx et al. 2011a). Various
ble, these elements are distributed mostly upon the tempo- explanations have been proposed for the existence of the ret-
ral tendon, the buccinator muscle, the most posterior zone romolar canal and its obvious nerve and vessels. Some
of the alveolar process, and the third mandibular molar. The authors have classified the retromolar canal as one of four
different paths which the retromolar mandibular canal may different types of bifid mandibular canals in the posterior
describe could be considered as a trait of discontinuous body of the mandible (Naitoh et al. 2009; Orhan et al. 2011),
variation, useful to typify ethnological material such as is the other three being the dental, forward, and buccolingual
studied in this paper, coming from a mestizo population canals (Chap. 16).
RMC MC
M3
MC RMF
STB M3
Fig. 17.4 Intraoperative view after flap elevation for the removal of the
lower right third molar in a 27-year-old female. A soft tissue bundle is
visible emerging from the retromolar foramen. M3 third molar, RMF
retromolar foramen, STB soft tissue bundle
M3
RMC
M2
M3al
Fig. 17.2 Axial CBCT image showing the retromolar canal posterior
STB
to the crown of the mandibular third molar. M3 third molar, RMC retro-
molar canal
CP
Fig. 17.5 Intraoperative view after removal of the lower right third
molar in a 24-year-old male. The soft tissue bundle exiting the retromo-
CM lar foramen has been preserved. M3al empty alveolus after removal of
RMF third molar, M2 second molar, STB soft tissue bundle
La
M2
Fig. 17.3 Superior view of the left retromolar area with a retromolar
foramen in a dry mandible. CM condyle of mandible, CP coronoid pro-
cess, La lingula, M2 second molar, RMF retromolar foramen
Presence of Retromolar Canal 371
Presence of Retromolar Canal Sawyer and Kiely (1991) described a significant positive
correlation of an accessory mandibular foramen with a retro-
The frequency of the retromolar canal commonly reported molar foramen regarding same-side occurrence. This rela-
in bilateral CBCT studies ranges from 5.0 to 16.1 % per tionship was also reported by Ossenberg (1987). In certain
side and from 8.5 to 28.1 % per patient (Table 17.1). study samples, a retromolar foramen was approximately
Figures reported in dry skull studies, however, show a twice as common in skulls with an accessory mandibular
much higher variation with regard to the frequency of ret- foramen as in sides without the trait. The incidence of a tem-
romolar canals/foramina compared to CBCT studies. Data poral crest may be related to the occurrence of a retromolar
of five regional lineages published by Ossenberg (1987) foramen, but a morphological association has not yet been
showed a trend of higher incidence of the retromolar fora- investigated.
men in recent descendants than in ancestral populations, A possible relationship between the dimensions of the ret-
but without significant difference. Interestingly, the ratio romolar trigone and the presence of the retromolar foramen
of bilateral to unilateral retromolar foramina was higher was evaluated by Bilecenoglu and Tuncer (2006) in 40 dry
in populations with a high frequency of foramina, but human mandibles. Neither the transverse width (mean
high-frequency populations tended to have the foramen 7.0 mm) nor the sagittal length (mean 9.4 mm) of the retro-
more often on the left. Five of nine samples tested by molar trigone was correlated with the presence of a retromo-
Ossenberg (1987) demonstrated a marginal preponder- lar foramen.
ance of retromolar foramina in males without reaching a Superiority of CBCT over panoramic radiography in
statistical significance. Also Pyle et al. (1999) found a identification of the retromolar canal has been shown by von
higher rate of retromolar foramina in male skulls (9.6 %) Arx et al. (2011b) (Figs. 17.6 and 17.7). While CBCT dem-
than in female skulls (6.1 %) but without a statistical sig- onstrated 31 canals in 121 sides, only 7 of these 31 canals
nificant difference. In the CBCT study by von Arx et al. were visible on the panoramic radiographs. Similarly,
(2011b), females (28.1 %) presented a retromolar canal Muinelo-Lorenzo et al. (2014) evaluated the visualization of
more often than males (22.8 %), but again without reach- retromolar canals in panoramic radiography versus CBCT. Of
ing statistical significance. 40 retromolar canals observed with CBCT, only 13 were
Regarding age profile, Ossenberg (1987) reported a peak identified with panoramic radiographs. Kaufman et al.
incidence in the adolescent cohort. The CBCT study by von (2000) presented a case with bilateral retromolar canals dis-
Arx et al. (2011b) demonstrated a higher occurrence of a ret- cernible on preoperative CT scans before implant provision,
romolar canal in individuals < 20 years of age (25 %) than in but those canals could not be identified on a panoramic
patients > 40 years of age (15.6 %), but the difference was not radiograph taken at the same time. Similarly, Han and Park
statistically significant. One may speculate that the retromo- (2013) described two cases with visualization of the retro-
lar foramen might be related to the adolescent growth spurt molar canals in CBCT scans but not with panoramic radio-
and to the eruption of the third molars due to an increased graphs. CBCT was also found to be superior compared to CT
neurovascular requirement. In a recent study including the and panoramic radiography in detailing the canal structures
largest study sample published to date (680 patients with of bilateral retromolar canals in a Japanese cadaveric sample
bilateral CBCT) neither demographic factors (gender, age) (Fukami et al. 2012). In a radiographic study comparing
nor the spatial resolution of the CBCT had a statistically sig- CBCT and CT, three retromolar canals were equally detected
nificant impact on the frequency of the retromolar canal (Filo and visible using both radiographic imaging techniques
et al. 2015). (Naitoh et al. 2010).
372 17 Retromolar Canal
MF
MF
MC
RMC
MC
M3
MC M3
MC
Fig. 17.7 The retromolar canal is clearly visible in the sagittal CBCT
Fig. 17.6 The absence of a retromolar canal is noted in this panoramic image of this same patient. MC mandibular canal, MF mandibular fora-
radiograph of the mandibular retromolar area in a 46-year-old male. men, M3 deeply impacted third molar, RMC retromolar canal
MC mandibular canal, MF mandibular foramen, M3 deeply impacted
third molar
374 17 Retromolar Canal
Course and Types of Retromolar Canals retromolar fossa to the radicular portion of the third molar
was by far the most frequent type of retromolar canal in the
Various courses and types of the mandibular retromolar study by Patil et al. (2013).
canal have been described (Ossenberg 1986; Narayana et al. The angle between the mandibular canal and the retromo-
2002; von Arx et al. 2011b; Patil et al. 2013; Kawai et al. lar canal at the bifurcation was measured by Orhan et al.
2014) (Figs. 17.8, 17.9, 17.10, and 17.11) and morphological (2011). The superior angle measured on average 128° on the
patterns can be summarized. The retromolar canal: right side and 134° on the left side, whereas the inferior
angle was 48.2° on the right side and 40.4° on the left side.
• Branches from the mandibular canal behind the third However, frequencies between sides did not differ
molar and courses upward to the retromolar fossa in a significantly.
more or less straight direction (subtype gives off anterior In a survey of 242 dry mandibles, the foramen had a
canal to the molars) smooth opening facing upward and backward (Narayana
• Branches from the mandibular canal behind the third et al. 2002). The authors speculated that the geometry of the
molar, continues initially in an anterior direction, and then opening indicated the entry of the neurovascular bundle from
curves backward and upward to the retromolar fossa (sub- the posterior aspect, thus potentially escaping the inferior
type gives off anterior canal to the molars) alveolar nerve block.
• Branches from the mandibular foramen and continues A recent study on temporal crest canals (TCC) in Japanese
anteriorly in a more or less horizontal direction to open on cadaveric mandibles using CBCT and dissection showed a
the anterior face of the ascending ramus or upper part of frequency of four TCC in 48 mandibles (8.3 %) and five TCC
the retromolar fossa in 90 observation areas (5.6 %) (Kawai et al. 2014). Three
• Does not originate from the mandibular canal but courses TCC started at the mandibular foramen and bifurcated from
from the retromolar fossa downward and anteriorly to the the mandibular canal in the ramus to exit the anterior bone
radicular portion of the third molar surface below the coronoid process. The other two TCC
originated from a separate foramen above the mandibular
The so-called temporal crest canal arises from a double or foramen, coursed anteriorly, and had the foramen on the
accessory mandibular foramen above and typically anterior anteromedial surface inferior to the coronoid process (Kawai
to the mandibular foramen and passing onto the anterior/ et al. 2014). Han et al. (2014) evaluated the presence of TCC
anteromedial face of the ascending ramus below the coro- in 446 patients who had undergone CBCT scanning. Six
noid process or in the upper part of the retromolar fossa. TCC were present in four of 446 patients (0.9 %). All TCC
Data about the course of the retromolar canal is limited were observed in males. All posterior foramina were located
(Table 17.2). Conflicting data were reported by three studies superior to the mandibular foramina on the medial aspect of
with two studies showing a straight upward canal to be the the ramus. One TCC was only slightly curved and uniformly
most frequent trajectory (Narayana et al. 2002; von Arx et al. wide, while the other 5 TCC were noticeably curved and
2011b). In contrast, a retromolar canal descending from the narrowing.
a b
Fig. 17.8 Illustration of retromolar canal: (a) vertical type, (b) vertical type with anterior branch
Course and Types of Retromolar Canals 375
a b
Fig. 17.9 Illustration of retromolar canal: (a) curved type, (b) curved type with anterior branch
a b
Fig. 17.10 Illustration of retromolar canal: (a) horizontal type, (b) aberrant type
376 17 Retromolar Canal
a b
Fig. 17.11 Illustration of temporal crest canal: (a) higher location, (b) lower location
Size and Height of Retromolar Canal 1.6 mm at the origin and 1.0 mm at the opening, which is
similar to the values reported by von Arx et al. (2011b)
The reported mean height of the retromolar canal based on (0.99 mm) and by Filo et al. (2015) (1.03 mm). In both
data from CBCT studies ranges from 8.4 to 14.8 mm and studies, the diameter of the retromolar canal was measured
the mean diameter from 0.99 to 1.6 mm (Table 17.3) 3 mm below the bone surface. Ossenberg (1987) measured
(Fig. 17.12). The mean diameter of the retromolar canal the actual retromolar foramen in 2500 mandibles with sizes
appears to be dependent on the type (Patil et al. 2013). ranging from 0.5 to 3 mm, but no mean value was
Straight or curved canals (type “A”) had a mean diameter of provided.
Table 17.3 Mean length (mm) and diameter (mm) of retromolar canal (RMC) or retromolar foramen (RMF)
Mean diameter of Mean diameter of
Author(s) Study material N Mean length of RMC RMC RMF
Ossenberg (1987) 2500 mandibles from NA – – 0.5–3.0 (mean NA)
museum collections
Narayana et al. (2002) 6 dry mandibles, 9 canals (> 5 mm) 8.7–20.3 (mean NA) 1.5–4.35 (mean NA)
injection of radiopaque
dye in RMF, then
radiography
Naitoh et al. (2009) 122 patients (CBCT) 24 canals 14.8 (7.2–24.5) – –
(mean age
50.8 ± 15.1 years, range
17–78 years)
Orhan et al. (2011) 242 patients (CBCT) 75 canals 13.5 (right 13.4, left – –
(mean age 36.7 years, 13.5); no significant
range 17–83 years) difference for gender
or sides
von Arx et al. (2011b) 100 patients (CBCT) 31 canals 11.3 ± 2.36 (7.4–18.2) 0.99 ± 0.31 (0.5–1.8) –
(mean age 36.1 years, (males had higher No significant
range 16–83 years) values than females, difference for age or
p = 0.025) gender
Patil et al. (2013) 171 patients (CBCT) 34 canals of type – At origin: 1.6 (0.8–3.6) –
(mean age 38 years, “A” At exit: 1.0 (0.2–2.3)
range 15–79 years) 137 sites with a – Not measured but –
total of 207 canals all < 1 mm
of type “B”
1 canal of type – At origin: 3.0 –
“C” At exit: 2.0
Orhan et al. (2013) 63 children (CBCT) 14 canals 11.4 (right 11.3, left – –
(mean age 12.3 years, 11.4); no significant
range 7–16 years) difference for gender
or sides
Han and Hwang 446 patients (CBCT) 45 canals – 1.13 ± 0.38 mm –
(2014) (age range 15–70 years) (0.6–2.0 mm)
Muinelo-Lorenzo et al. 225 patients (CBCT) 40 canals Length: 6.9 ± 2.8 mm 1.6 ± 0.7 mm 1.6 ± 0.6 mm
(2014) (mean age 43.9 years, Height: 8.4 ± 3.4 mm
range 13–79 years)
Filo et al. (2015) 680 patients (CBCT) 216 canals Height: 10.2 ± 2.6 mm 1.03 ± 0.27 mm –
(mean age 29.9 years,
range 8.7–89.6 years)
378 17 Retromolar Canal
Table 17.4 Distance (mm) from retromolar foramen (RMF) or retromolar canal (RMC) to adjacent anatomical structures
Author(s) Study material N Distance from RMF to
Bilecenoglu and Tuncer (2006) 40 dry mandibles 12 canals Distal aspect of 2nd molar (n = 4):
11.9 ± 6.71 mm (9.5–24.3 mm)
Distal aspect of 3rd molar (n = 8):
4.23 ± 2.30 mm (2.4–8.2 mm)
von Arx et al. (2011b) 100 patients (CBCT) (mean age 31 canals Distal aspect of 2nd molar:
36.1 years, range 16–83 years) 15.2 ± 2.39 mm (12.3–22.2 mm)
Measurements were taken from
midpoint of RMF); younger individuals
had longer distances than older
individuals (p = 0.062)
Patil et al. (2013) 171 patients (CBCT) (mean age 38 34 canals Distal alveolar crest of 3rd molar:
years, range 15–79 years) of type “A” 7.0 mm (0.8–15.7 mm)
137 sites with a total of Distal alveolar crest of 3rd molar:
207 canals of type “B” 7.1 mm (1.0–18.3 mm)
1 canal of type “C” Distal alveolar crest of 3rd molar:
14.3 mm
Han and Hwang (2014) 446 patients (CBCT) (age range 45 canals Distal aspect of 2nd molar:
15–70 years) 14.08 ± 3.85 mm (8.5–24 mm)
Filo et al. (2015) 680 patients (CBCT) (mean age 216 canals Distal aspect of 2nd molar:
29.9 years, range 8.7–89.6 years) 15.1 ± 2.83 mm (2.8–24.8 mm)
Neurovascular Content of Retromolar Canal 379
Neurovascular Content of Retromolar Canal In a 35-year-old female patient, routine surgical removal
of a third mandibular right molar was performed, when a soft
Scarce but consistent information is available regarding the tissue formation thought to be a neurovascular bundle was
elements of the mandibular retromolar canal. Some studies incidentally found posterior to the osteotomy site. The soft
have histologically evaluated the neurostructural elements tissue bundle was ligated, retrieved, and subjected to a histo-
within the canal (Schejtman et al. 1967), while others have logical examination. The specimen (7 × 4 × 2 mm) included
analyzed the soft tissue bundle emerging from the retromolar striated muscle fibers, thin myelinated nerve fibers, numer-
foramen (von Arx et al. 2011a) (Figs. 17.13, 17.14, 17.15, ous venules, and a muscular artery having a lumen of 120 ×
17.16, and 17.17). 130 μm (Bilecenoglu and Tuncer 2006).
Regarding the most frequently found components of the In a 19-year-old female patient referred for removal of her
canal, a histological study of 18 cadaveric heads reported in wisdom teeth, the panoramic radiograph showed bilateral
decreasing order, a myelinated nerve, one or more arterioles, retromolar canals in the mandible. The patient consented to
and one or more venules (Schejtman et al. 1967). perform cone beam computed tomography and to take a
380 17 Retromolar Canal
biopsy from the soft tissue bundle exiting the retromolar arteries of various sizes without a clear positional relation-
foramen during the surgical removal of her lower right wis- ship. Regarding the radiographic techniques, CBCT was
dom tooth. The histology showed multiple myelinated nerve superior in detailing the retromolar canal compared to CT
fibers grouped into smaller (diameter 40–60 μm) and larger and panoramic radiography.
(diameter 80–180 μm) nerve fascicles that were encircled by Dissection of five Japanese cadaveric mandibles present-
a dense collagen capsule (perineurium). The nerve fascicles ing transcrestal canals in CBCT revealed histologically the
ran parallel to blood vessels (arteries, venules, and capillary presence of nerves and vessels (Kawai et al. 2014).
vessels). The maximal size of the largest arteries was 600 μm. Using magnetic resonance imaging of six fresh frozen
Numerous adipocytes were present between the nerve fasci- cadaveric mandibles with subsequent cryomicrotome sec-
cles and blood vessels (von Arx et al. 2011a). tioning, the inferior alveolar nerve (IAN) and its branches
Fukami et al. (2012) investigated a Japanese cadaveric were investigated (Ikeda et al. 1996). The authors reported
mandible and its bilateral retromolar canals using panoramic that the retromolar branch separated from the IAN at the
radiography, CT, CBCT, and histology. The latter showed mandibular foramen, had a 2- to 5-mm course parallel to the
that the retromolar canal contained several nerve bundles and IAN, and then turned upward posterior to the third molar.
RMF
MF RMC
RMC
M3 M3
MC
MC
RMCb
MC
MC
BV
STB
BV NF
APC NF NF
RMF NF
NF
APC
APC
third molar Fig. 17.16 Histology of the excised soft tissue bundle from the retro-
molar foramen demonstrates multiple nerve fascicles with blood ves-
sels and numerous adipocytes (HE staining) (Histology by Prof. Dr.
D. Bosshardt, University of Bern, Switzerland) (Copyright von Arx
et al. 2011a). APC adipocytes, BV blood vessels, NF nerve fascicles
BV
Fig. 17.15 The intraoperative view after flap elevation for removal of P
the lower right third molar shows a soft tissue bundle emerging from the NF
retromolar foramen (Copyright von Arx et al. 2011a). RMF retromolar
P P
foramen, STB soft tissue bundle
APC NF
P
NF
APC P
APC
Fig. 17.17 Higher magnification of Fig. 17.16 shows that each nerve
fascicle is surrounded by a thick perineurium (Copyright von Arx et al.
2011a). APC adipocytes, BV blood vessels, NF nerve fascicles, P
perineurium
382 17 Retromolar Canal
Clinical Relevance of Retromolar Canal mandible via the retromolar foramen. As such, the mandibu-
lar nerve bypasses the normal course through the mandibular
The retromolar canal may carry an aberrant branch of the foramen and may escape anesthesia during routine mandibu-
long buccal nerve, as described in three case reports (Singh lar block administration (Narayana et al. 2002; Blanton and
1981; Jablonski et al. 1985; Kodera and Hashimoto 1995). Jeske 2003).
Such an anatomic variation is clinically relevant for surgical In summary, the presence of a retromolar canal may be
procedures in the retromolar area such as removal of third the underlying cause of anesthesia failure in the posterior
molars, sagittal split osteotomy, bone harvesting in retromo- mandible and of the buccal mucosa. It was suggested to
lar and ramus areas, and removal of cysts and tumors as well employ a higher anesthetic technique (Gow Gates) or to give
as for intraoral dental anesthesia. additional local anesthesia in the retromolar fossa (Blanton
Singh (1981) observed a narrow soft tissue bundle exiting and Jeske 2003; Boronat and Penarrocha 2006). Damage to
a small foramen in the retromolar fossa after flap elevation the neurovascular structure of the retromolar canal or exit-
for surgical removal of a lower wisdom tooth. The structure ing/entering the retromolar foramen may result in marked
then ran laterally from the foramen for about 20 mm, before bleeding, temporary or permanent sensitivity changes of the
passing under the reflected flap in an anteroinferior direction. supplied areas, or traumatic neuroma formation. Further, the
The soft tissue bundle was subsequently damaged, and a retromolar foramen may present an entry point, and the ret-
small biopsy was excised for histologic analysis confirming romolar canal may act as a route of infection or tumor metas-
the presence of a 0.5-mm-wide nerve with mainly myelin- tases (Fanibunda and Matthews 2000; Bilecenoglu and
ated nerve fibers. The postsurgical follow-up revealed pares- Tuncer 2006).
thesia of the ipsilateral vestibular sulcus and gingiva
extending from the retromolar to the canine area.
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Mental Foramen
18
The mental foramen is the end point of the mental canal localized during a surgical procedure in this area (Figs. 18.1
emerging from the mandibular canal. As such, it conducts and 18.2). On the other hand, the prominent location of the
neurovascular structures from the body of the mandible to its mental foramen also holds the risk of damaging the mental
lateral surface. The mental foramen is used as a landmark to nerve with subsequent dysesthesia, temporary or permanent
divide the hemimandible into anterior and posterior parts. sensitivity changes, and forensic issues (von Arx 2013).
The zone between bilateral mental foramina is also known as In contrast to other foramina of the maxillary bones, the
the interforaminal region, a term widely used in dental mental foramen is normally visible on conventional and pan-
implantology with respect to the placement of implants in oramic radiographs (Shibli et al. 2012) (Figs. 18.3 and 18.4).
the anterior mandible. In the vertical dimension, the mental Using three-dimensional radiography, such as CBCT, the
foramen lies between the tooth-bearing alveolar process position of the mental foramen can be accurately determined
(upper portion) and the basal body of the mandible (lower as well as its relationship to adjacent roots, to retained teeth,
portion) (Solar et al. 1994). In cases with severe vertical or to bone lesions. Further, distances from the mental fora-
bone atrophy, the mental foramen may be at risk for surgical men to neighboring structures can be measured accurately
damage due to its proximity along the superior border of the using CBCT (Figs. 18.5 and 18.6). A recent review found
mandibular body. that CBCT imaging is the optimal imaging technology to
Since the mental foramen is prominently located on the determine the accurate location of the mental foramen
external surface of the mandible, it is normally easily (Aminoshariae et al. 2014).
MeF
STB
Fig. 18.1 Intraoperative view after flap elevation in the right mandible Fig. 18.2 Intraoperative view after placement of one dental implant
showing a soft tissue bundle exiting the mental foramen in a 45-year- anterior and two implants posterior to the mental foramen
old female. MeF mental foramen, STB soft tissue bundle
MC
MC
MeF MeF
MC
MC
MeF MeF
18 Mental Foramen 387
PM1
PM 2
MeF
MeF
Fig. 18.5 Sagittal CBCT image showing the distance (yellow line) MeC
between the mental foramen and the adjacent root of the right mandibu-
lar first premolar in the mesiodistal plane of a 55-year-old female. MeF
mental foramen, PM1 first premolar
Fig. 18.6 Coronal CBCT image showing the distance (yellow line)
between the mental foramen and the adjacent root of the right mandibu-
lar second premolar in the buccolingual plane. MeC mental canal, MeF
mental foramen, PM2 second premolar
388 18 Mental Foramen
Position of Mental Foramen With regard to the topographical position of the mental
foramen to adjacent teeth, the location may be determined in
The mental foramen is located on the lateral surface of the the sagittal plane (mesiodistal orientation) as well as in the
mandible, usually in the area of the premolars (Fig. 18.7). vertical plane (craniocaudal orientation). Within the axial
Within the buccal cortex, the opening of the mental foramen plane (mediolateral orientation), the mental foramen is
is commonly directed posterosuperiorly (Fig. 18.8). In the always located lateral to the adjacent roots, unless a tooth is
vertical plane, the mental foramen is located approximately malpositioned with its root penetrating the buccal cortex.
in the middle third of the mandible in a dentate adult, in the When documenting the position of the mental foramen, most
lower third of the mandible in a child, and in the upper third studies and textbooks refer to the sagittal plane. The majority
of the mandible in edentulous patients. In individuals who of cadaveric and radiographic studies have reported the men-
have been edentulous for several years, the mental foramen tal foramen be located immediately below the second premo-
may even be located along the superior aspect of the mandi- lar (18–77.6 %) or in the area below between the first and
ble due to a complete resorption of the alveolar process second premolars (6–59.8 %) (Table 18.1). Some studies
(Figs. 18.9, 18.10, 18.11, and 18.12). In a study evaluating have reported a relatively high frequency (28.5–32 %) of the
panoramic radiographs of 173 edentulous patients, the men- mental foramen located in the area below between the sec-
tal foramen was located at the crest of the ridge in 7.2 % of ond premolar and mesial root of first molar (Moiseiwitsch
females and in 6.7 % of males (Güler et al. 2005). In such 1998; Cutright et al. 2003; Gupta 2008).
situations, the clinician is advised to use extreme caution Shah et al. (2010) presented a case with bilateral location
when performing crestal incisions in the premolar area of the mental foramen below the mesial root of the first
(Figs. 18.13, 18.14, and 18.15). Sofat et al. (2013) calculated molar. In contrast, more anterior locations of the mental fora-
the vertical bone loss above the mental foramen comparing a men below the first premolar (up to 18.7 %) or in the area
ratio of bone height measurements taken in panoramic radio- below the canine and first premolar (up to 4.6 %) are less
graphs of 30 dentate and of 60 edentulous patients. In the common. Even more rare is a position of the mental foramen
dentulous sample, the ratio between the distance from the immediately below the mesial root of the first molar (up to
crestal bone level to the inferior mandibular border and the 4.5 % incidence). The wide variation of possible locations of
distance from the inferior margin of the mental foramen to the mental foramen in the sagittal plane calls for a careful
the inferior mandibular border was 2.9 ± 0.28 in males and and individual radiographic assessment prior to any anes-
3.1 ± 0.42 in females. Hence, the foramen was located in the thetic, endodontic, or surgical intervention in the canine to
upper part of the lower third of the body of the mandible. the first molar area of the mandible.
Applying the same ratios to edentulous patients, the mean Comparing right and left sides of the same individual,
bone loss over the mental foramen was calculated as the mental foramen is often symmetrically located, with
3.6 ± 2.29 mm in males and 6.6 ± 2.86 mm in females. percentages of complete symmetry reported from 44 to
In a radiographic study evaluating the distances from the 79 % (Al Khateeb 2007; Chkoura and El Wady 2013; Chu
mental foramen to the alveolar ridge in children and adoles- et al. 2014). Santini and Alayan (2012) compared the posi-
cents, significant differences were reported for three age tion of the mental foramen in 76 Chinese, in 46 European,
groups with the shortest mean distance (11.7 mm) in 6- to and in 33 Indian adult dry skulls. In Chinese skulls, the
12-year-old children and the longest mean distance mental foramen was most frequently in line with the long
(13.2 mm) in 16–18-year-old adolescents (Orhan et al. 2013). axis of the second premolar, whereas in the European and
Some studies have assessed the proximity of the mental Indian skulls, it was commonly located between the first
foramen to the adjacent premolar root apices. Ozturk et al. and second premolars. The comparison of prenatal (54
(2012) obtained a mean distance of 1.81 mm (range fetuses between 17 and 32 weeks of gestation) and postna-
0–4.5 mm) in CT scans of 52 adult dry skulls. In CBCT tal samples (94 panoramic radiographs of children aged
scans of 168 patients, the mean distance from the mental 4–12 years) showed that the mental foramen moves in a
foramen to the nearest root surface was 5.0 mm (range 0.3– posterior direction during the development of the mandible
9.8 mm) (von Arx et al. 2013). A similar mean distance of (Balcioglu et al. 2011).
4.0 mm (range 2.1–12.5 mm) was reported by Kalender et al. Only scarce information is available regarding the vertical
(2012) who assessed CBCT scans of 193 patients. Carruth position of the mental foramen relative to adjacent root api-
et al. (2015) assessed the distance between the center of the ces. In a study evaluating panoramic radiographs of 860
mental foramen and a horizontal line through the apex of the patients (mean age 24 ± 7 years, range 12–77 years), the
second premolar using sagittal CBCT scans. The calculated mental foramen was found above/at/below the level of the
mean distance was 2.8 ± 2.86 mm. premolar apices in 3.7 %/18.6 %/77.7 %, respectively (Al
Position of Mental Foramen 389
Khateeb 2007). With advancing age, the authors observed a measured from 15.5 to 16.6 mm (Moiseiwitsch 1998; Neiva
more frequently inferior position of the mental foramen. A et al. 2004; Guo et al. 2009).
mental foramen radiographically projected over the apex of In edentulous patients, the missing teeth cannot be uti-
an adjacent root may mimic a periapical lesion (Figs. 18.16, lized as a reference for locating the mental foramen, and
18.17, 18.18, and 18.19). intra- or extraoral palpation of the mental foramen may also
Measurements of the distance from the mental foramen to be inaccurate. Therefore, two cadaver studies have assessed
the midline of the symphysis have yielded mean values rang- the position of the mental foramen in relation to the cheilion
ing from 22 to 28 mm (Table 18.2). In the vertical plane, (corner of the mouth) (Song et al. 2007; Guo et al. 2009).
mean distances from the mental foramen to the lower border These authors reported that the mental foramen was located
of the mandible have been reported to be 12–16.5 mm and to on average 20.4–24 mm inferior and 3.3–3.6 mm medial to
the upper border 12–20.4 mm (Fig. 18.20). Due to crestal/ the cheilion. However, extraoral soft tissue reference points,
periodontal bone loss, some authors have suggested to use such as the cheilion, may be dependent on ethnicity, and the
the cementoenamel junction of adjacent teeth rather than the values given above should not be used as standard dimen-
crestal bone level as a reference, with mean distances sions for any race.
PM2
PM 2 PM 1
MeF
AMF
Fig. 18.7 Decorticated left mandible of dry skull showing the location
of the mental foramen close to the apex of the second premolar. MeF
mental foramen, PM2 second premolar
MeF
MC MeF
MeF
Fig. 18.9 Sagittal CBCT image showing the location of the mental
foramen along the mandibular body due to a complete resorption of the
edentulous alveolar process in a 79-year-old female. MC mandibular
canal, MeF mental foramen
MeF
MeF
MeF
AMF
MeF
MeF crestal
MeF incision
STB
vestibular
release
incision
Fig. 18.14 The coronal CBCT section demonstrates the close proxim-
ity of the mental foramen with the crest of the alveolar process. MeF
mental foramen
Table 18.1 Location of mental foramen in sagittal plane related to adjacent teeth
Author(s) Study material N Location of mental foramen (in %)
Below Below Below Below Below Below Below
C* between C PM1 between PM2 between M1
and PM1 PM1 and PM2 und M1
PM2
Shankland (1994) 68 mandibles 136 – – – 6 77.6 11.9 4.5
(Indians)
Al Jasser and 397 panoramic 794 – 0.6 5.3 42.7 45.3 5.2 0.9
Nwoku (1998) radiographs (Saudis)
(mean age 28.8 years,
14–64 years)
Moiseiwitsch 55 cadavers (white 100 – 1 5 41 18 31 4
(1998) North Americans)
Cutright et al. 76 cadavers (Whites) NA – – 7 32 51 10 –
(2003) 78 cadavers (Blacks) NA – – – 14 53 32 1
Neiva et al. (2004) 22 cadavers 44 – – – 58 42 – –
(Caucasians)
Hwang et al. 30 cadavers (Koreans) 60 – – 13.3 16.7 63.3 6.7 % –
(2005)
(continued)
392 18 Mental Foramen
MC
MC
*
Fig. 18.17 The panoramic radiograph demonstrates that the mental foramen projects over the apex of the left mandibular second premolar (arrow)
and mimics a periapical lesion (compare also with the somewhat lower location of the mental foramen [arrowhead] on the patient’s right side)
12.0 -
20.4 mm 22.0 -
28.0 mm
12.0 -
16.5 mm
MeF Fig. 18.20 Reported mean values for the linear distances of the mental
foramen to the midline, superior, and inferior borders of the mandible
(see text)
MeC
Fig. 18.19 The coronal CBCT section confirms the absence of a peri-
apical lesion at the root canal-filled second premolar. The radiolucency
seen on the panoramic radiograph corresponds to the mental foramen.
MeC mental canal, MeF mental foramen
Table 18.2 Distances (mm) from mental foramen (MF) to midline, upper and lower borders of mandible
MF to lower MF to upper
MF to midline border of border of MF to cementoenamel
Author(s) Study material N of mandible mandible mandible junction of closest tooth
Phillips et al. (1990) 75 mandibles 150 – Right: 13.9a
(10.9–16.4)
Left: 14.5a
(11.7–15.8)
Moiseiwitsch (1998) 55 skulls (white North 100 – – – 16 (8–21)
Americans)
Cutright et al. (2003) 76 skulls (Whites) 78 – 22a – – –
skulls (Blacks) (20.1–23.5)
Neiva et al. (2004) 22 skulls (Caucasians) 44 27.6 ± 2.3 12 ± 1.7 (9–15) – 15.5 ± 2.4 (12–22)
(22–31)
Smajilagi and 20 mandibles – Right: Right: – –
Dilberovi (2004) 25.7 ± 1.89 13.3 ± 1.1
Left: Left:
24.8 ± 1.99 14.6 ± 1.33
Position of Mental Foramen 395
Size of Mental Foramen mental foramen has an oblique and funnel-shape opening
within the thick buccal cortex.
Cadaveric and radiographic studies have assessed the size of An interesting and new aspect has been recently docu-
the mental foramen (Table 18.3). Mean mesiodistal length of mented by measuring the size of the MF with ultrasonogra-
the foramen measures 2.3–4.6 mm, and mean vertical height phy in 20 patients with persisting neurosensory dysfunction
is 1.76–3.7 mm, indicating that the mental foramen has an (NSD) with a duration ≥ 1 year and following unilateral
oval shape with a greater sagittal than vertical dimension removal of third molars (Moystad et al. 2015). Control sides
(Figs. 18.21 and 18.22). The large discrepancies for mea- presented a larger mean size of the MF (2.5 mm) compared
surements among different studies may be explained by vari- to NSD sides (2.1 mm). The authors speculated that damage
ous methods of size assessment. Additionally, accurate to the IAN may lead to a degeneration of the mental nerve
measurement of the size of the foramen is difficult since the and eventually to a size reduction of the mental foramen.
1.8 - 3.7 mm
2.3 -
4.6 mm
Fig. 18.21 Reported mean values in the literature for the width and
height of the mental foramen (see text)
Radiographic Visibility of Mental Foramen (Table 18.4) (Ramadhan et al. 2010; von Arx 2013; Ahmed
et al. 2015; Iwanaga et al. 2015) (Figs. 18.27, 18.28, 18.29,
In a study comparing panoramic radiography and CBCT in and 18.30). The presence of AMF appears to be dependent
100 children (mean age 12.3 years), the mental foramen was on ethnicity. A study evaluating skulls of 81 different popu-
seen in 44.5 % of panoramic radiographs, although none lations reported the highest frequency of AMF in skulls from
with good visibility, and in 100 % of CBCT scans with good Central Asia (up to 32 %) and in skulls from sub-Saharan
visibility in 98.5 % of the cases (Cantekin et al. 2014). In Africa (up to 29 %) (Hanihara and Ishida 2001). In contrast,
another study assessing 412 panoramic radiographs, the the frequency of AMF in skulls from Eastern Europe was
mental foramen was visible in 84.2 % (Jalili et al. 2012). below 5 %. Another study found AMF in 9 % of skulls of
After tracing the mental foramen on 75 adult dry skulls with pre-Columbian Nazca Indians, but only in 1.4 % of skulls of
wires, panoramic radiographs visualized the mental foramen twentieth-century Caucasian Americans (Sawyer et al.
with 100 % frequency and periapical radiographs in 75 % of 1998).
cases (Phillips et al. 1992a, b). The reasons for failure of Recent radiographic studies using CBCT (Naitoh et al.
visualization in periapical radiographs included the location 2009, 2011; Oliveira-Santos et al. 2011; Kalender et al.
of the mental foramen off the film, masking the mental fora- 2012) or CT (Haktanir et al. 2010; Sisman et al. 2012)
men by a root, or multiple radiolucencies. reported a 1.3–7.4 % frequency of AMF per hemimandible
Bou Serhal et al. (2002) compared panoramic radiogra- and a 2–11.9 % frequency per patient.
phy, CT, and intraoperative measurements regarding the dis- Only little information has been presented regarding the
tance from the alveolar crest to the mental foramen in 22 distribution of the nerve exiting the AMF (Toh et al. 1992;
sites scheduled for implant placement. While panoramic Mamatha et al. 2013; Iwanaga et al. 2015). It appears that the
radiography overestimated the distance by a mean of 0.6 mm, innervation pattern of nerves (AMN) leaving the AMF is
CT underestimated the distance by a mean of 0.3 mm com- dependent upon the positions of the MF and the AMF,
pared to the measurements taken during surgery. Also, pan- because the fibers of the AMN supplement some areas where
oramic radiography showed more intraobserver variation the MN is not distributed (Iwanaga et al. 2015).
(−2.62 to 1.86 mm) compared to CT (−0.11 to 0.82 mm). Prevalent locations of AMF with respect to the proper
The authors therefore recommended the use of cross- mental foramen differ widely among studies. Mean sizes of
sectional imaging for preoperative planning in the mental AMF range between 0.93 and 1.95 mm, hence are consider-
foramen area. ably smaller than the actual mental foramen. When the size
Pyun et al. (2013) compared panoramic radiographs and of an AMF exceeds half the size of the true mental foramen,
CT scans of 100 patients (mean age 48.4 ± 11.8 years) to it was suggested to use the term double mental foramen
assess a possible correlation of the linguobuccal trajectory of (Oliveira-Santos et al. 2011; von Arx et al. 2014). Usually,
the mandibular canal and the position of the mental foramen. two-dimensional radiography fails to show AMF (Imada
Based on their findings, the position of the mental foramen in et al. 2014). The number of AMF detection in a sample of
panoramic radiographs was affected by the horizontal course 127 cases was significantly higher using CBCT (7.4 %) com-
of the mental foramen canal. A significant change in direc- pared to panoramic radiography (1.2 %) (Neves et al. 2014).
tion of the mandibular canal was observed below the first With regard to the soft tissue bundle exiting AMF, it usu-
molar irrespective of the anteroposterior position of the men- ally contains myelinated nerve fibers accompanied by small
tal foramen. blood vessels and adipocytes (von Arx et al. 2014). Damage
to an accessory mental nerve can result in temporary or per-
manent sensitivity change with the distribution area of the
Number of Mental Foramina soft tissue consistent with damage to the mental nerve, but to
a comparatively smaller area (Concepcion and Rankow
In general, there is one single mental foramen on each side of 2000; von Arx et al. 2014).
the mandible. In very few patients, the mental foramen has An AMF to be considered as such should have a separate
been reported to be absent or hypoplastic (Manikandhan canal emerging from the mandibular canal or branching from
et al. 2010; da Silva et al. 2011; Oliveira-Santos et al. 2011; the mental canal (Fuakami et al. 2011; Kalender et al. 2012).
Lauhr et al. 2015) (Figs. 18.23, 18.24, 18.25, and 18.26). The further distant accessory foramina are located from the
Interestingly, no sensory deficits were reported in those mental foramen, the less likely they communicate with the
patients (da Silva et al. 2011; Lauhr et al. 2015). mandibular or mental canals and thus should not be referred
A more frequent finding are double or multiple mental to as AMF, but rather, they should be denoted as “additional
foramina, also termed accessory mental foramina (AMF) buccal foramina” (Fuakami et al. 2011; von Arx et al. 2014).
Number of Mental Foramina 399
Fig. 18.23 A 3D reconstructed CBCT image showing a hypoplastic Fig. 18.24 A mental foramen (arrowhead) of typical size is present on
mental foramen (arrow) on the right side in 71-year-old female the left side of the mandible
a b
MeF MeF
Fig. 18.26 The axial CBCT image (inferior view) demonstrates the
different sizes of the bilateral mental foramina. MeF mental foramen
Table 18.4 Frequency, size (mm), distances (mm) and position of accessory mental foramina (AMF)
Mean size and
Author(s) Study material N Frequency distances Comments
Shankland (1994) 68 mandibles (Indians) 136 6.6 % – –
Sawyer et al. (1998) Skulls (from twentieth 468 (Indians) Indians: 1.5 % – –
century): 234 Indians, 332 (African African Americans:
166 African Americans) 5.7 %
Americans, 255 white 510 (white Americans) White Americans:
Americans. 50 100 (Nazca Indians) 1.4 %
pre-Columbian skulls Nazca Indians: 9 %
of Nazca Indians
Agthong et al. 110 skulls (Asians) 220 1.8 % – –
(2005)
Katakami et al. 16 patients (CBCT) 17 AFM – Horizontal size: 1.6 41 % posterior to MF
(2008) (mean age NA) (0.7–2.6) 29 % inferior to MF
Vertical size: 1.2 12 % posteroinferior to
(0.5–2.2) MF
Median horizontal
distance to MF: 2.0
(0–7.4)
Median vertical
distance to MF: 0.5
(0–3.6)
Naitoh et al. (2009) 157 patients 314 Patients: 7 % Size: 1.9 ± 0.6 60 % posteroinferior to
(Japanese) (CBCT) Sides: 4.1 % (1.1–2.9) MF
(mean age Area: 11× unilateral AMF 2×
51.5 ± 14.9 years, 1.7 mm2 ± 1.5 mm2 unilateral with 2 AMF
range 17–77 years) Distance to MF: each
6.3 ± 1.5 (4.5–9.6)
Haktanir et al. 100 patients (Turks) 200 Patients: 4 % Size: 1.3 (0.7–2.0) 3× unilateral AMF
(2010) (multi-detector CT) Sides: 2.5 % Distance to midline: 1× bilateral AMF
(mean age 27.2 (24.5–30.4)
43.4 ± 15.3 years, Distance to alveolar
range 17–73 years) crest: 13.4
(9.4–16.6)
Naitoh et al. (2011) 365 patients 730 Patients: 7.7 % Area: 1.5 mm2 23× unilateral AMF
(Japanese) (CBCT and Sides: 4.1 % ± 0.9 mm2 7× unilateral with 2 AMF
panoramic (0.3–3.9 mm2) each
radiography) (mean Distance to MF: 48.6 % of AMF (or AMF
age 51.7 ± 15.1 years, 6.4 ± 3.3 (1.1–13.6) canal) were seen on
range 17–83 years) panoramic radiographs
Number of Mental Foramina 401
PM2 PM1 C
AMF
AMF
ABF
MeF
MeF
PM2 PM1 C
AMF MeF
MC
Fig. 18.30 The intraoperative view after flap elevation for apical sur-
Fig. 18.29 The axial CBCT image demonstrates that the accessory gery of the second premolar shows the accessory mental foramen. AMF
mental foramen and the mental foramen are separated by a bone spic- accessory mental foramen, C root of mandibular canine, MeF mental
ule. AMF accessory mental foramen, MC mandibular canal, MeC men- foramen, PM1 root of mandibular first premolar, PM2 root of mandibu-
tal canal, MeF mental foramen, MIC mandibular incisive canal lar second premolar
Mental Canal and “Anterior Loop” 403
Mental Canal and “Anterior Loop” An anterior loop of the mental canal is highly relevant
clinically when performing surgical procedures in the inter-
The bony canal that branches from the mandibular canal and foraminal region, in particular when installing endosseous
courses toward the mental foramen is called the mental canal implants (Wismeijer et al. 1997; Liang et al. 2008). When
(Fig. 18.31). The length and diameter of the mental canal implants are placed between the mental foramina, it is impor-
was determined by dissection of 80 cadaveric hemimandi- tant that they are separated as much as possible for biome-
bles of Chinese origin (Xu et al. 2015). The mean length of chanical reasons (Ritter et al. 2012). The most posterior
the mental canal was 4.01 ± 1.20 mm (range 2.20–8.04 mm). implant should thus be placed as close to the mental foramen
The mean diameter of the mental canal amounted to or to the anterior loop as possible. Therefore, the anterior
2.60 ± 0.60 mm (range 1.65–4.06 mm). In the vertical plane, loop has gained wide interest in the field of implant dentistry
the mental canal commonly coursed upward, meaning that (Rosenquist 1996). Many cadaveric or radiographic studies
the origin of the mental canal from the mandibular canal was have assessed the presence and the extent of the anterior loop
located below the level of the mental foramen. In CT, this (Table 18.5). The frequency of an anterior loop ranges from
distance was calculated to be on average 2.54 ± 0.53 mm 13.3 to 100 % with a mean mesial extent up to 7 mm.
(range 1–3.8 mm) (Forni et al. 2012) and in cadaveric heads However, the two studies reporting 88 % and 100 % fre-
4.5 ± 1.9 mm (Hwang et al. 2005). Ozturk et al (2012) mea- quency, respectively, used mechanical devices (tubes,
sured the distance from the superior margin of the mental probes) inserted via the mental foramen into the mental canal
foramen to the superior border of the mandibular canal at the to evaluate the presence of an anterior loop and to measure
lowest point of the mandibular canal. The mean distance was the mesial extent of the loop (Arzouman et al. 1993; Neiva
5.36 mm (range 0–9 mm). et al. 2004). Both methods, however, carry the risk of overes-
In the horizontal plane, three different courses have been timation of the presence and mesial extent of the anterior
described (Kieser et al. 2002): a course in an anterior direc- loop since the tube or probe may have mistakenly be
tion, a perpendicular course, and a curved course with a advanced into the mandibular incisive canal (Chap. 21).
posterior direction toward the terminal portion of the canal. From a clinical point of view, manipulation of the mental
The latter anatomical configuration of the mental canal is canal is not recommended due to the hazard of neurovascular
also called “anterior loop.” The course of the mental canal damage. However, a three-dimensional radiographic assess-
appears to be ethnically influenced. In skulls of Caucasians, ment is suggested for preoperative analysis of an existing
a posterior course of the mental canal prevailed (in 86.7 %), anterior loop. In a study comparing cadaveric dissection and
whereas in Blacks, a perpendicular course (in 45.8 %) was CBCT, Uchida et al. (2009) demonstrated a high concor-
the most frequent course (Kieser et al. 2002). The emerging dance of the radiographically determined mesial extent of
pattern of the mental canal was also evaluated in 52 adult the anterior loop with corresponding anatomical configura-
dry skulls by Ozturk et al. (2012). A sharp turn was tion. In contrast, panoramic radiographs were found provid-
observed in 53.2 %, a soft curved exit in 29.8 %, and a ing inaccurate results regarding identification of the anterior
straight path in 17 %. loop of the mental canal (Kuzmanovic et al. 2003).
MIC MC
MC
MeC
MeF
Fig. 18.31 Axial CBCT scan showing the anterior loop of the mental
canal (dotted line) in a 68-year-old female. MC mandibular canal, MIC
mandibular incisive canal, MeC mental canal, MeF mental foramen
404 18 Mental Foramen
Table 18.5 Frequency and extent (mm) of “anterior loop” of mental canal
Author(s) Study material N Loop (in %) Mesial extent of loop
Arzouman et al. (1993) 25 mandibles (probing of mental – 100 % 6.95
canal)
25 mandibles (panoramic – – 2.75 (without radiopaque
radiography) marker)
4.64 (with radiopaque
marker)
Bavitz et al. (1993) 24 cadavers (anatomical 47 sides (24 dentate, 23 – Dentate: 0.2 ± 0.3
dissection) edentulous) Edentulous: 0 ± 0
Li et al. (2013) 68 Chinese patients (CT) (mean 136 sides 83.1 % (sides) 2.09 ± 1.34 (0–5.31)
age 40 years, range 21–61 years) Males: 2.42 ± 1.38
(0–5.31)
Females: 1.77 ± 1.22
(0–4.39)
Gender difference was
significant
von Arx et al. (2013) 142 patients (CBCT) (mean age: 167 sides 69.1 % All: 1.6 (0–5.6)
39.7 years, range 10–86 years) Only cases with loop: 2.3
(0.9–5.6)
The mesial extension
was > 4 mm in 4.2 %
Xu et al. (2015) 40 cadaveric mandibles 80 sides – 3.54 ± 0.70 (1.92–6.31)
(dissection)
406 18 Mental Foramen
Mental Nerve An indirect damage to the mental nerve may also occur,
albeit rarely, following a stretching injury to that nerve due to
The mental nerve carries afferent sensory fibers and is one of implant placement into a large mandibular incisive canal
the two terminal branches of the inferior alveolar nerve, the engaging the mandibular incisive nerve (Uchida et al. 2007)
other one being the mandibular incisive nerve. The mental (Chap. 21).
nerve normally has three to four mental, labial, and gingival The fine lower labial branches of the mental nerve are
branches supplying the skin of the lower lip, the corner of the particularly vulnerable when performing relatively minor
mouth, and the chin, as well as the vestibular gingiva and surgical procedures, e.g., excision of benign soft tissue
mucosa from the second premolar to the midline of the sym- lesions, on the inner aspect of the lower lips because they run
physis (Figs. 18.32 and 18.33). Since the individual branches close to the mucosal surface. Alantar et al. (2000) suggested
of the mental nerve can be separately followed into the man- that injuries to the lower labial branches could be prevented
dibular canal, loss of sensitivity is dependent upon which if the incisions are made horizontally on the dorsal aspect of
branch of the mental nerve has been mechanically or chemi- the lower lip at an angle of approximately 36 degrees with
cally damaged (Hu et al. 2007). Thus, disturbance of the respect to the long axis of the lip when, for example, per-
mental nerve may cause selective sensitivity loss due to its forming biopsies of the minor salivary glands or excising
segmentation. mucosal nodules. The same authors also suggested a
Won et al. (2014) studied the innervation pattern of the U-shaped incision below the mucogingival line and parallel
mental nerve in ten cadaveric specimens using Sihler’s stain- to the course of the lower labial branches for bone harvesting
ing method and dissection. In five cadavers, overlapping ter- procedures in the symphysis, actually avoiding vestibular
ritories were observed for the branches of the mental nerve, release incisions.
whereas in the other five specimens, the branches were dis- On the other hand, Alsaad et al. (2003) reported that there
tributed individually without overlap. In six cases, the is no safe anatomical space for minor surgical procedures
branches of the mental nerve anastomosed with the long buc- applied to the inner mucosal aspect of the lower lip if avoid-
cal nerve of CN V and in some cases even anastomosed with ance of cutaneous numbness is an important consideration.
the marginal mandibular and cervical branches of the facial Based on their cadaveric lip dissection study, they suggested
nerve (CN V) near the mental foramen. an oblique mucosal incision 1.5 cm lateral to the midline in
To avoid surgical damage to the mental nerve and its an inferolateral direction to avoid damaging the vertical and
branches, caution must be exercised when performing oblique lower labial branches. However, the reported inci-
mucosal incisions. Adequate distances must be observed dence (3–4 %) of sensory deficits following minor labial sali-
and flaps should be raised carefully. When approaching the vary gland surgery is generally low (Richards et al. 1992;
mental foramen, one should use gauze attached to a hemo- Marx et al. 1998).
stat rather than periosteal elevators to detach the soft tis- Pogrel et al. (1997) described an anatomical variation of
sues from the bone. Further, the neurovascular bundle the mental nerve that reenters the labial plate anteriorly to
emerging from the mental foramen should be protected supply the lower incisors. In 15 % of 20 evaluated hemi-
with gauze during drilling procedures in the surrounding mandibles, unequivocal evidence of nerve fibers of the men-
areas. The use of rotary instruments close to the mental tal nerve reentering the anterior labial bone cortex was
nerve must be considered a high-risk procedure. demonstrated with half of the cases showing substantial mid-
Alternatively, utilization of Piezosurgery-driven instru- line crossover. The authors concluded that the mental nerve
ments should be considered. No soft tissue retractors or may act as an “accessory” nerve to the lower incisors in
periosteal elevators should be positioned on the soft tissue some patients and may require additional labial infiltration in
bundle exiting the mental foramen. crossover situations.
Mental Nerve 407
lower lip
lower lip
FA
3 ILA
1 2
DLI
DAO MeN
2 3
DLI 1
4
MeF
MeN
FA
Fig. 18.32 Dissection of the left cadaveric mandibular body depicting
MeA
the mental nerve consisting of three branches (the depressor anguli oris
muscle overlying the mental nerve has been partially resected and
folded anteriorly). DAO depressor anguli oris muscle, MeF mental fora-
men, MeN mental nerve (with three branches)
Fig. 18.33 Dissection of the left cadaveric mandibular body showing
the mental nerve consisting of four branches (the depressor anguli oris
muscle overlying the mental nerve has been resected). DLI depressor
labii inferioris muscle, FA facial artery, ILA inferior labial artery, MeA
mental artery, MeN mental nerve (with four branches)
408 18 Mental Foramen
Clinical Relevance of the Mental Foramen bone removal is necessary immediately adjacent to the men-
and Related Structures tal foramen and nerve.
Occasionally, accessory mental foramina are detected
The area of the mental foramen is of particular interest to pre- or intraoperatively. The soft tissue bundle exiting sup-
clinicians performing anesthesia, endodontics, and implant plementary mandibular buccal foramina, such as double or
surgery in the premolar region (Greenstein and Tarnow accessory mental foramina, often contains sensory nerves,
2006). Block anesthesia of the mental nerve is relatively easy and caution must be exercised during surgery in the vicinity
and safe with only minimal risk of intraneural or intravascu- to avoid sensory deficits. The risk of postsurgical numbness
lar injection. Though the mental foramen may be located appears to be higher in cases presenting a double mental
close to adjacent root apices, the inadvertent extrusion of foramen compared to cases with an accessory mental fora-
infected debris into the mental foramen or direct damage by men or with so-called additional buccal foramina.
over-instrumentation is not to be expected. More likely is the The “anterior loop” of the mental canal remains the most
indirect irritation of the mental nerve by irrigation solutions, debatable anatomical structure in the premolar area since
especially sodium hypochlorite (NaOCl), or by extrusion of some authors claim that the mandibular incisive canal, i.e.,
medicaments (calcium hydroxide) and obturation materials the anterior continuation of the mandibular canal, is mistak-
(Mohammadi 2010). enly interpreted as the anterior loop. Others have shown that
An unusual case of lower lip paresthesia following place- even with CBCT, the loop is not always clearly discernible.
ment of an extensive pin-retained amalgam restoration in a As a consequence, it has been suggested to maintain a safety
mandibular second premolar was reported by Abbott (1997). zone of at least 5 mm mesial to the mental foramen thus
Radiographs indicated that the mental foramen was close to avoiding potential damage to the anterior loop of the mental
the apex of this tooth, and it was assumed that postoperative canal when present.
pulpitis and periapical inflammation had caused the pares-
thesia through the effects of pressure on the mental nerve.
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Lingual and Mylohyoid Nerves
19
Lingual Nerve medial ridge of the retromolar triangle (Fig. 19.3). At the
level of the posterior root of the third molar, the lingual
The lingual nerve arises from the posterior trunk of the nerve usually is covered only by the gingival mucoperios-
mandibular nerve at a mean distance of 13.5–14.3 mm teum. At the upper border of the mylohyoid line, the lin-
below the foramen ovale (Table 19.1) (Fig. 19.1). The lin- gual nerve continues horizontally on the superior surface
gual nerve is the largest branch of the mandibular nerve of the mylohyoid muscle and courses in close relation to
with a mean diameter ranging between 2.03 and 3.62 mm the upper pole of the submandibular gland, giving off
(Table 19.2). The lingual nerve courses lateral to the tensor fibers to the submandibular ganglion. In the close vicinity
veli palatini and medial to the lateral pterygoid muscle of the upper surface of the posterior portion of the mylohy-
(Fig. 19.2). Approximately at the lower border of the lat- oid muscle, the submandibular duct crosses over the lin-
eral pterygoid muscle, the lingual nerve is joined by the gual nerve. After passing along the lingual bone plate of
chorda tympani at a mean distance of 8.4–11.4 mm infe- the mandibular body, the lingual nerve turns medially
rior to the origin of the lingual nerve or at a mean distance toward the tongue usually at the level of the first or second
of 15.1 mm below the foramen ovale, respectively mandibular molar (Fig. 19.4) (Klepacek and Skulec 1994;
(Table 19.1). The lingual nerve then crosses the medial Chan et al. 2010; Boffano et al. 2012; Benninger et al.
pterygoid muscle on its anterolateral surface, passes below 2013). The lingual nerve carries general sensory fibers as
the mandibular attachment of the pterygomandibular well as gustatory and secretomotor fibers via chorda tym-
raphe, and eventually approaches the lingual bone surface pani of CN VII to the tongue, floor of the mouth, and sub-
posterior to the third molar, in an area also described as the lingual and submandibular glands
MN
MA
MA
LN
IAN ChT
IAA
LN
IAA
IAN
LN
MHN
CP
MA
LPM
LN
R
LN
MPM
IAN MPM
RMTmr
LN
MPM MPM
RMT
MPM M3
LN
Border
UP Communications of Lingual Nerve
of tongue
Fig. 19.5 Pattern of origin of lingual nerve from mandibular nerve mandibular foramen, (c) furcation in the lower half of the distance
(Based on Kim et al. 2004). (a) Furcation above sigmoid notch, (b) between sigmoid notch and mandibular foramen, (d) plexiform branch-
furcation in the upper half of the distance between sigmoid notch and ing pattern
Position of Lingual Nerve Relative to Mandible 417
from the mylohyoid nerve at the level of the intermediate gual nerve deep to the lateral pterygoid muscle above the
digastric tendon to join the lingual nerve. The authors specu- upper edge of the medial pterygoid muscle. In 19 %, the
lated that such a communicating branch might help in func- junction was located in the superior half of the medial ptery-
tional recovery following lingual nerve damage. goid muscle. The mean diameter of the chorda tympani was
0.68 ± 0.1 mm.
Chorda Tympani
Position of Lingual Nerve Relative
The chorda tympani conveys secretomotor fibers and taste to Mandible
afferents via the lingual nerve to the submandibular and sub-
lingual glands and the tongue, respectively (Fig. 19.6) (Zur Since the lingual nerve is at risk of iatrogenic injury during
et al. 2004). According to McManus et al. (2011), the chorda various surgical procedures (mainly third molar removal) or
tympani may have additional sensory and secretomotor func- mandibular block anesthesia, it has gained considerable atten-
tions. The chorda tympani originates from the facial nerve tion among dentists and oral and maxillofacial surgeons.
(CN VII) within the temporal bone and passes anterosuperi- Because there are no clear intraoral landmarks to identify the
orly in the posterior canaliculus to enter the middle ear. After trajectory of the lingual nerve along the posterior mandible,
crossing the middle ear, the chorda tympani exits through the cadaveric and radiographic studies have evaluated the position
petrotympanic fissure, aka, Glaserian fissure, fissura spheno- of the lingual nerve relative to the posterior mandible (Figs. 19.7
petrosa, into the infratemporal fossa where it joins the lin- and 19.8) (Table 19.3). A significant number of lingual nerves
gual nerve at an angle of between 24° and 28° (Bartsch et al. may be located above the alveolar bone in the gingival tissues
1991; McManus et al. 2012). The extraosseous portion of the (up to 17.6 %) or may contact the bone in the third molar area
chorda tympani is about 1.3–3 times longer than the intraos- (up to 62 %) (Table 19.3). Consequently, there is no doubt that
seous part with the latter showing greater individual varia- the lingual nerve is highly vulnerable in this region. The sur-
tions due to the individual distinctions in the structure of the geon cannot rely on the lingual plate to act as a protective bar-
temporal bone (Bartsch et al. 1991). Erdogmus et al. (2008) rier to the lingual nerve during third molar extraction, since the
assessed the chorda tympani in 42 sides of 21 adult male lingual nerve may lie above the bone in this area (Kiesselbach
cadaveric heads. In 81 %, the chorda tympani joined the lin- and Chamberlain 1984; McGeachie 2002).
TGG
MN
FN
LN
ChT
FN
LN
2.3 mm
8.3 mm
25–62 %
0.6 mm 9.3 mm
Fig. 19.7 Reported minimum and maximum mean values for the verti-
cal and horizontal position of the lingual nerve (represented by the yel-
low circle) relative to the lingual alveolar crest and lingual bone plate,
respectively Fig. 19.8 Reported range of percentages for the lingual nerve (repre-
sented by the yellow circle) in direct contact with the lingual bone plate
A very high and exposed location of the lingual nerve at incision. A recent literature review reported an incidence of
or above bone level in the retromolar area was found to be temporary LN deficit after third molar surgery ranging from
significantly correlated with the atrophy of the mandibular 0 to 23 % and of permanent LN damage varying between 0
crest Hölzle and Wolff (2001). In contrast, Pogrel et al. and 8 % (Boffano et al. 2012).
(1995) reported no statistical relationship of the nerve posi-
tion with the presence or absence of posterior teeth. They
speculated that only little resorption of the lingual plate Risk Factors of Lingual Nerve Injury
occurs in the retromolar trigone region when posterior teeth
are lost. Pogrel et al. (1995) emphasized in their study com- Brann et al. (1999) evaluated postsurgical neural deficits
prising lingual nerve dissections in 20 cadaveric heads that after removal of 718 lower third molars. Lingual nerve dam-
no bilateral relationship of nerve position was evident. As an age was five times more frequent when the teeth were
example, one specimen displayed a lingual nerve that was at removed under general rather than local anesthesia. The find-
the level of the bone crest on one side, yet it was positioned ing could not be explained in terms of surgical difficulty,
11 mm inferior to the crest on the other side. They concluded preoperative pathology, age, or anatomical position.
that the position of the nerve in a specific location on one Valmaseda-Castellon et al. (2000) assessed the risk factors for
side did not predict the contralateral position. lingual nerve damage in 1117 consecutive surgical removals
of lower third molars. Lingual flap retraction, vertical sec-
tioning of the tooth, surgeon inexperience, lingual angulation
Risk of Lingual Nerve Injury of the tooth, and prolonged operating time significantly
increased the risk of nerve damage.
The removal of mandibular third molars is the most fre- Renton and McGurk (2001) investigated risk factors for
quently performed procedure by oral and maxillofacial sur- temporary and permanent lingual nerve injury after extraction
geons (Bouloux et al. 2007), and it is the most common of mandibular third molars based on 2134 consecutive cases.
surgical procedure associated with lingual nerve deficit The incidence of temporary and permanent lingual nerve
(Boffano et al. 2012) (Table 19.4) (Fig. 19.9). Hölzle and injury was 1 and 0.3 %, respectively, per tooth. Factors that
Wolff (2001) assessed the position of the lingual nerve rela- predicted temporary and permanent lingual nerve injury by
tive to the typical distal release incision for third molar univariate analysis were age, depth of application, difficulty of
removal in 34 cadaveric heads. The mean distance between operation, surgeon, and surgical technique used. Independent
the lingual nerve and the incision line was 4.41 ± 1.44 mm. In risk factors identified by multivariate analysis for temporary
one specimen, the lingual nerve was sectioned by the release lingual nerve injury were perforation of the lingual plate,
Risk Factors of Lingual Nerve Injury 419
Table 19.3 Distances (mm) between lingual nerve (LN) and posterior mandible
Study Region of
Author(s) material N interest Vertical distance Horizontal distance Other Comments
Kiesselbach 34 adult 34 sides Third molar *2.28 ± 1.96 0.59 ± 0.9 (0–3) 62 % of LN *Measured from
and cadaveric (2 mm above contacted the lingual crest
Chamberlain heads crest – 7 mm lingual plate;
(1984) below crest) 17.6 % of LN were
at or above the
alveolar crest
256 patients 256 Third molar – – 4.5 % of LN were Intraoperative
with third sides found above the assessment after
molar alveolar bone crest careful exposure of the
extraction LN
(age NA)
Pogrel et al. 20 cadaveric 40 sides Retromolar *8.32 ± 4.05 3.45 ± 1.48 (1–7) 5 % of LN were *Measured from point
(1995) heads pad (closest “oblique” found above crest “A” defined as the
distance to LN of lingual plate and transition site from the
was 4.45 ± 1.48) 2.5 % at the crest horizontal to the
vertical portion of the
ramus
Miloro et al. 10 20 sides Third molar *2.75 ± 0.97 2.53 ± 0.67 (0–4.4) 25 % of LN *Measured from
(1997) volunteers (0.5–4.6) contacted the lingual crest
(MRI) (mean lingual plate;
age 10 % of LN were at
24.7 years, or above the
range 21–35 alveolar crest
years)
Behnia et al. 430 fresh 669 Third molar *3.01 ± 0.42 2.06 ± 1.10 (0–3.2) 14.05 % of LN *Measured from
(2000) cadaveric sides (1.7–4.0) located above lingual crest
heads lingual crest,
0.15 % in
retromolar pad and
85.8 % near or
below the lingual
crest;
22.3 % of all LN
directly contacted
the lingual bone
plate
Hölzle and 34 adult 68 sides Retromolar 7.83 ± 1.65 0.86 ± 1.0 (0–4) In 8.8 %, the LN Measured from point
Wolff (2001) cadaveric area (4.5–14) was at or above the “A” defined as the
heads alveolar crest; transition site from the
57.5 % of LN horizontal to the
contacted the vertical portion of the
lingual plate ramus
Kim et al. 16 adult 32 sides Retromolar 7.8 (3.5–14.2) – – Measured from lingual
(2004) Korean area crest (none of the LN
cadaveric Distal aspect 9.5 (5.1–16.1) ran above the crest)
heads of Third
molar
Mesial aspect 15.5 (8.7–19.9)
of Third
molar
Karakas et al. 11 adult 21 sides Third molar 9.5 ± 5.2 4.1 ± 1.9 – Radiographs were
(2007) cadaveric taken after dissection
heads and marking the nerves
(continued)
420 19 Lingual and Mylohyoid Nerves
permanent deficits (Hillerup and Jensen 2006). The same bundle traumatization by a sharp needle tip, movement of the
authors evaluated 42 lingual nerve injuries following man- needle itself, extra- or intraneural hemorrhage from trauma
dibular block anesthesia. They found no difference in the to blood vessels, or the neurotoxic properties of the local
severity of nerve injury with or without the experience of an anesthetic (Pogrel et al. 1995; Smith and Lung 2006; Morris
“electric shock” felt by the patient during administration of et al. 2010). The prognosis of nerve injuries after dental
the anesthesia. They concluded that “electric shock” per se is injection is generally good, regardless of the presence or
probably of minor relevance for the etiology of injection absence of electric shock sensation. Spontaneous complete
injuries. Neither was the injected volume nor repeat injec- recovery from the altered sensation occurs within 8 weeks in
tions associated with the severity of nerve injury. 85–94 % of cases. However, patients with paresthesia lasting
A recent study on 1000 mandibular block anesthesias beyond 8 weeks after the initial injury have less chance of
reported a temporary disturbance of the lingual nerve in six full recovery (Smith and Lung 2006). Lingual nerve micro-
cases only (van der Sleen et al. 2015). There was no long- surgery may improve sensory function in those patients
term injury to the lingual nerve caused by administering (Ziccardi and Zuniga 2007). A more diverse strategy of man-
local anesthetics. agement of neural injuries has been described by Renton and
It is unknown whether it takes an intrafascicular injection Yilmaz (2012) including reassurance, counseling, cognitive
to produce an injection injury or whether injection in close behavior therapy, systemic and topical medication, and
proximity to a nerve may cause neurotoxic damage (Hillerup exploratory surgery.
and Jensen 2006). In a study evaluating 248 cases of pares-
thesia after dental local anesthetic administration, most cases
involved mandibular block anesthesia (94.5 %), and the lin- Clinical Relevance of Lingual Nerve
gual nerve was affected in 89 % of the examined cases
(Garisto et al. 2010). A similar predilection of the lingual General and special (taste) sensation of the tongue and ante-
nerve (79.1 %) was reported by Gaffen and Haas (2009) in a rior floor of the mouth is only achieved with a functional
study assessing 182 cases with nonsurgical paresthesia fol- lingual nerve. As such, the lingual nerve is associated with
lowing intraoral local anesthesia. many aspects of daily life, and injuries can markedly distress
According to Pogrel et al. (2003), the most plausible the quality of life of affected patients because of the negative
explanation for predilection of the lingual nerve to develop impact on speech, taste, swallowing, ability to maintain food
paresthesia after a mandibular block is the fact that it often is and liquid competence, social interactions, the playing of
unifascicular at the level of the lingula contrasted by the mul- wind musical instruments, and pain perception. Lingual
tifascicular inferior alveolar nerve. The authors speculated nerve damage can cause drooling, tongue biting, a burning
that a unifascicular nerve may be injured more easily than sensation of the tongue, burns on the tongue from hot food
one with multiple fascicles and may further demonstrate less and drinks, pain, change in speech pattern, and/or a change
power of spontaneous recovery. They also reported that the in taste perception of food and drink (Pichler and Beirne
pattern of lingual nerve injury always affected the full distri- 2001). In addition, chronic pain has been observed as a fre-
bution of the nerve and did not appear to indicate damage to quent symptom after local anesthesia-induced nerve injury
just one or two fascicles (Pogrel et al. 2003). (Renton et al. 2010).
The proximity of the needle relative to the lingual nerve Significant life changes including adverse effects on
was evaluated in sham mandibular block anesthesia per- employment, relationship changes, and depression have also
formed in 44 cadaveric heads with subsequent dissection been reported as long-term consequences of lingual nerve
(Morris et al. 2010). In 4.5 % of the simulated injections, the deficits (Pogrel et al. 2011). Most lingual nerve injuries
needle penetrated the lingual nerve. The average minimum result in sensory changes that are temporary and recover
distance between the needle and the lingual nerve was spontaneously with time (Bagheri et al. 2010; Cheung et al.
0.73 ± 0.70 mm (range 0–3.0 mm), and in every case the nee- 2010; Renton et al. 2012). However, lingual sensory impair-
dle passed the lingual nerve at a distance smaller than the ment remains a clinical problem in oral and maxillofacial
diameter of the nerve. The authors concluded that the surgery and has important medical and legal implications.
assessed proximity of the lingual nerve to the path of needle The latter aspect is not only addressing the doctor’s embar-
placement during a standard landmark-based mandibular rassment of causing damage but it also relates to an increased
block injection and the large degree of anatomic variability focus on patient complaints, litigation, and malpractice suits
in the nerve position makes lingual nerve injury difficult if (Hillerup 2007; Boffano et al. 2012).
not impossible to avoid. The (surgical) removal of mandibular third molars
Several mechanisms have been proposed to explain lin- remains the most frequent cause of injury to the lingual
gual nerve damage during the administration of anesthesia nerve as well as to the inferior alveolar nerve. From an ana-
with a mandibular block injection including neurovascular tomical perspective, it is the proximity of these nerves to the
Mylohyoid Nerve 423
Mylohyoid Nerve
SML
IAN
MHN
MHM
MF
M3
MHG La
branching pattern of the mylohyoid nerve. Branches to the study compared two groups each with 14 voluntary adults
anterior belly of the digastric muscle and to the mylohyoid regarding pain scoring using a visual analog scale. In group A,
muscle as well as fibers to the submandibular gland were local infiltrations were administered for ipsilateral mylohyoid
observed in all specimens. Periosteal branches to the medial and buccal nerves. In group B, inferior alveolar and buccal
cortex of the mandible were seen with a frequency of 80 %, nerve blocks were performed. The authors concluded that anes-
thin connecting branches to the lingual nerve in 30 % of the thesia of the mylohyoid nerve represents an alternative for anes-
specimens, and cutaneous branches in 70 % of the cases. thesia regarding implant placement in the posterior mandible.
The diameter of the mylohyoid nerve was evaluated in
five fresh adult cadaveric heads at the level of the mylohy-
oid muscle (Tubbs et al. 2007). The mean diameter at this Literature
location was 1.0 mm (range 0.75–1.2 mm). The same
authors also suggested considering the mylohyoid nerve for Altug HA, Sencimen M, Varol A, Kocabiyik N, Dogan N, Gulses
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placement at the edentulous posterior mandibular ridge. J Oral
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Bagheri SC, Meyer RA, Khan HA, Kuhmichel A, Steed
MB. Retrospective review of microsurgical repair of 222 lingual
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chorda tympani from the tympanic cavity and its course until its entry
It is well documented that the mylohyoid nerve provides into the lingual nerve (in German). Anat Anz. 1991;173:243–6.
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Anterior Mandible
20
The anterior mandible is generally defined as the part of the the visibility of the lower incisor teeth, drooling, and den-
mandible rostral to the mental foramina, and hence, it is also ture instability (Zide and McCarthy 1989; Noia et al. 2012;
called the interforaminal region (Fig. 20.1). The latter term is Hur et al. 2013).
widely used in dental implantology, and it was introduced in In a dissection study of 20 Korean cadaveric heads, the
the early phase of modern implant dentistry reflecting the upper fibers of the mentalis muscle were intermingled with
concept of implant-borne removable, and later fixed, full the inferior margin of the orbicularis oris muscle in all speci-
mandibular prostheses (Almog et al. 2007) (Fig. 20.2). mens, and lateral fibers of the mentalis muscle joined the
Another term frequently used to describe the anterior man- depressor labii inferioris muscle (Hur et al. 2013). Fibers of
dible is “symphysis.” By definition, the word “symphysis” in the mentalis muscle may also blend with the ipsilateral lower
anatomy means the fibrocartilaginous fusion of two bones. bundle of buccinator muscle fibers (D’Andrea and Barbaix
As such, it is a misnomer for the anterior mandible since the 2006). The junction of the mentalis and orbicularis oris mus-
mandible consists of a single bone, but embryologically cles forms the labiomental fold. If a significant overlap
forms from two halves that fuse and ossify early in life occurs, the fold is indistinct. If the orbicularis oris is narrow,
(Nyström and Ranta 2003). The symphysis has also been the fold is high (Garfein and Zide 2008). Fat tissue is nor-
defined as the area bounded by distal imaginary vertical lines mally present deep to the mentalis and orbicularis oris mus-
through the lower canine teeth (Goodday 2013). cles, and volume loss of deep fat contributes to the aging
The chin (l: mentum) denotes the lower and most anterior process (Rohrich and Pessa 2009).
portion of the mandible, and it is often the most forward skel- The blood supply to the anterior mandible is primarily
etal part of the head (pogonion = most anterior point of the from three sources (Romanos et al. 2012) including the infe-
chin in midsagittal plane) (Fig. 20.3). The chin is the area rior alveolar artery, submental artery from facial artery, and
where autogenous block grafts are frequently harvested or sublingual artery from lingual artery (Chaps. 21 and 22).
genioplastic surgeries and osteosynthesis of mandibular Similarly, the sensory innervation of the anterior mandible
fractures are performed (Alatel and Al Majid 2012; Goodday has multiple origins including the mandibular incisive (aka
2013; Park et al. 2013). Usually, a bony and bilateral mental incisive nerve or incisive branch of the inferior alveolar
protuberance is present at the anterior lower border of the nerve), mental, mylohyoid, and lingual nerves (Chaps. 18,
mandible. Above the chin is a slight concavity called the 19, 21, and 22). The main sensory nerve of the anterior man-
incisive fossa (Fig. 20.4). This area provides attachment for dible is the (mandibular) incisive nerve as the continuation of
the bilateral mentalis muscle. the inferior alveolar nerve, supplying the mandibular ante-
Dissection of 14 cadaveric hemifaces found the origin of rior teeth (Wadu et al. 1997). In dentate subjects, small ter-
the mentalis muscle being located on average 18 mm above minal branches of the incisive nerve were found to cross the
the inferior border of the mandible (Hazani et al. 2013). midline to contribute to the innervation of the contralateral
The fan-shaped muscle descends into the skin of the chin incisors, whereas in edentulous subjects, such cross-
(Figs. 20.5, 20.6, 20.7, and 20.8), and it belongs to the innervation was not observed (Wadu et al. 1997). Damage to
lower group of the muscles of facial expression. It is inner- the mandibular incisive nerve, for example, during harvest-
vated by the lower branches of the facial nerve (CN VII). ing of bone block grafts from the chin region, often results in
The mentalis muscle provides the major vertical support of sensitivity changes to the anterior teeth (see below).
the lower lip and elevates the chin (Rubens and West 1989). Pogrel et al. (1997) reported that branches of the mental
Absence or malfunction of the mentalis muscle results in nerve might reenter the labial bone plate of the anterior
mandible to supply the lower ipsi- and contralateral inci- innervation appears to occur in mandibular central and lat-
sors, explaining the phenomenon of crossover innervation. eral incisors. They observed in a study with 38 subjects that
On the lingual aspect, terminal branches from the mylohy- the bilateral inferior alveolar nerve block success rates were
oid and lingual nerves may enter the lingual foramina in the significantly higher for the central and lateral incisors when
midline region (Madeira et al. 1978; Wilson et al. 1984; compared with the success rates of the unilateral inferior
Varol et al. 2009). Yonchak et al. (2001) reported that cross- alveolar nerve block.
IFo
IFo
MeF
SYM MeF
Fig. 20.4 Anterior view of an
edentulous dry mandible with
relevant anatomical features. IFo MeP MeP
incisive fossa, MeF mental
foramen, MeP mental
protuberance, SYM symphysis
432 20 Anterior Mandible
ILA
DLI
MeM IFo
MeN
IAN
MIN
er
ular bord
MeP Mandib
OO
DLI
MeN DAO
MeM MeM
Alveolar Ridge 433
Alveolar Ridge
OO
MeM MeM
Fig. 20.10 Recession of the facial gingiva (arrow) at the right man-
Fig. 20.9 Axial CBCT scan demonstrating that the anterior mandible dibular central incisor in a 23-year-old female
is the thinnest region (arrow) with regard to the width of the mandibular
alveolar process (44-year-old male)
a b
Dimensions of the Anterior Mandible ble ranges from 0.99 to 3.19 mm and from 1.24 to 2.80 mm,
respectively, depending on the site and level of measurement.
The buccolingual dimensions of the anterior mandible are sum- Lee et al. (2014) assessed CT images taken in 973 Korean
marized in Table 20.1. While the anterior mandible is narrow in patients (mean age 41.2 years). The mean interforaminal dis-
the crest area (3.6 mm in edentulous sites versus 6.4 mm in den- tance was 55.4 ± 5.13 mm. Root apices of anterior mandibular
tate sites), it is clearly larger in the lower half of the anterior body teeth were located on average 22.2 ± 3.84 mm above the infe-
(11.5–12.8 mm in dentate mandibles) (Fig. 20.12). The mean rior mandibular border and 5.2 ± 1.70 mm posterior to the
thickness of the buccal and lingual plates in the anterior mandi- labial cortical plate.
Genial Tubercles
The genial tubercles are often distributed as right and left pro-
tuberances and superior and inferior tubercles located at the
6.4 mm lower lingual aspect of the anterior mandible (Figs. 20.13,
20.14, and 20.15). The genial tubercles serve as points of
attachment for the genioglossus muscle (upper tubercles) and
for the geniohyoid muscle (lower tubercles) (Baldissera and
Silveira 2002). The genial tubercles may become relatively
prominent owing to a combination of calcification in the ten-
dinous insertion of the geniohyoid and genioglossus muscles
and atrophy of the mandible (van Leeuwen et al. 2014). These
authors also assessed 16 case reports describing isolated frac-
tures of the genial tubercles not associated with fractures of
the mandible. All patients (mean age 69 years) wore lower
dentures and displayed edentulous and atrophied mandibles.
Buccal Lingual
Mintz et al. (1995) assessed the location of the genial tuber-
1.24– cles relative to the mandibular incisor teeth in 41 dry skulls.
0.99–
2.80 mm The mean vertical distance from the tubercles to the apices of
3.19 mm
the central incisors was 6.45 ± 3.3 mm (range 1–14 mm). The
mean width and height of the tubercles was 5.95 mm (range
MIC
3–8 mm) and 4.8 mm (3–7 mm), respectively. All genial
tubercles were located below the central incisor apices.
11.5–12.8 mm Silverstein et al. (2000) evaluated the genial tubercles in
ten cadaveric heads following sagittal sectioning. The mean
thickness of the mandible at the level of the genial tubercles
was 12.6 ± 1.84 mm (range 9–15 mm). The mean distance
from the genial tubercle to the inferior border of the mandi-
ble was 14.2 ± 2.2 mm (range 12–18 mm). The width of the
genioglossus muscle measured at 2 mm from the tip of the
genial tubercles was 13.8 ± 0.79 mm (range 13–15 mm).
Yin et al. (2007) compared anatomical and CT measure-
Fig. 20.12 Cross section of the anterior mandible of a dry skull at the
ments of the superior genial tubercles in 40 Chinese adult
level of the lateral incisor showing relevant bone dimensions. MIC
mandibular incisive canal human skulls. The mean width and height were 6.98 ± 1.35 mm
and 5.82 ± 0.71 mm based on measurements derived from
cadaveric specimens and 7.01 ± 1.13 mm and 6.17 ± 0.71 mm
derived from CT measurements. The mean distance from the
inferior mandibular border to the lower margin of the genial
tubercles was 11.1 ± 2.05 mm anatomically and 10.4 ± 1.55 mm
radiographically. Anatomic and CT measurements were found
to be correlated.
A case report of an unusual oversized genial tubercle caus-
ing pain and discomfort in a 70-year-old female was presented
by Rubira et al. (2010). The length of the projection from the
lingual base to the tip of the bony spine measured 18 mm.
Genial Tubercles 437
MLFsu LiT
GTsu GTsu
LiT
MLFsu
GTsu GTsu
GTin GTin
MLFin
LLF LLF
MLF
GT GT
Fig. 20.13 Lingual view of a dry mandible showing the genial tuber-
cles. GTsu superior genial tubercle, GTin inferior genial tubercle, Fig. 20.15 Occlusal view of a dry mandible showing genial tubercles
MLFsu superior median lingual foramen, MLFin inferior median lin- with normal size. GT genial tubercle, MLF median lingual foramen,
gual foramen LLF lateral lingual foramen
438 20 Anterior Mandible
M2
MHR
MLFsu
Bone Harvesting from Symphysis The mean volume of a single block graft extending bilaterally
was 3.49 ± 0.77 cm3. The average dimension of the block graft
Mandibular cortical grafts are the gold standard in the resto- was 38.8 × 11.1 × 7.8 mm.
ration of intraoral osseous volume (Aalam and Nowzari Verdugo et al. (2010) measured the volume of one-piece
2007). The anterior mandible (chin region) provides a pri- bone grafts harvested from the chin in ten patients. The mean
mary site for intraoral harvesting of autogenous block grafts volume was 2.3 ± 0.4 mL (range 1.7–2.8 mL). The same
(Figs. 20.18 and 20.19). Convenient surgical access, proxim- authors also performed tomographic calculations from cross-
ity of donor and recipient sites, availability of larger quanti- sectional images in 40 patients to determine the volume of
ties of cortical and cancellous bone compared with other bone grafts that can be safely harvested from the chin. The
intraoral donor sites, minimal resorption, and no hospitaliza- mean volume was 1.4 ± 0.6 mL (range 0.5–2.7 mL). Yates
tion are the main advantages of this procedure (von Arx et al. (2013) harvested rectangular bone blocks on each side
2009). The chin region can provide adequate bone to aug- of the mandible in 59 cadaveric heads. The mean surface
ment an area previously occupied by up to six teeth (Cranin area per block was 359 mm2 (length × height) with a mean
et al. 2001). Several studies have assessed the volume of depth of 7.8 mm.
bone available for harvest from the anterior mandible while Di Bari et al. (2013) calculated the available bone volume
respecting safety margins with respect to adjacent structures in the anterior mandible observing 5-mm minimum distances
such as the apices of anterior mandibular teeth, mental to the mental foramina, apices of anterior teeth and inferior
foramina, lingual plate, and inferior border of the mandible. border of mandible, and leaving the lingual plate intact.
Montazem et al. (2000) quantified the amount of bone and CBCT scans of 100 patients were evaluated morphometri-
maximum graft size in 16 adult cadaveric heads. The mean cally. The overall mean graft volume was 2.87 mL with a
volume of a unilateral bone graft was 4.84 mL derived with mean cortical volume of 0.71 ± 0.23 mL and a mean cancel-
water displacement volumetry and 4.71 mL based on the vol- lous volume of 2.16 ± 0.76 mL. Brockhoff et al. (2014)
ume of a donor site impression. The average size of a unilat- assessed the graft volume obtained from the symphysis in 59
eral corticocancellous block graft measured 20.9 × 9.9 × 6.9 mm. cadavers. The mean volume of the block grafts was 1.29 mL
Yavuz et al. (2009) calculated the graft dimensions in 15 adult in dentate specimens and 1.35 mL in edentulous specimens.
patients using three-dimensional reconstruction of CT data. The difference was not statistically significant.
Fig. 20.18 Intraoperative view of two large autogenous bone blocks Fig. 20.19 The two block grafts measured approximately 18 mm in
harvested from the anterior mandible in a 67-year-old female. The left length and 10 mm in height. Holes for placement of fixation screws can
block has already been removed be seen
440 20 Anterior Mandible
MIN
MIN MIN
Fig. 20.20 Illustration showing the neural supply of the anterior man-
dibular teeth by the mandibular incisive nerve. Possible damage to its
branches depends on the size of the block graft (dotted rectangles).
MeN mental nerve, MIN mandibular incisive nerve
Fig. 20.22 Limiting the mucosal incision (red line) to the distal aspects
of the canines avoids damage to the branches of the mental nerve and
maintains sensitivity of the labial and mental soft tissues
Clinical Relevance of the Anterior Mandible 441
Noia et al. (2012) evaluated soft tissue changes in 30 localization of vital anatomical structures is essential.
patients (mean age 45 years) following chin bone graft har- Anatomical landmarks include the mental foramina, the
vesting. The comparison of preoperative and 6-month postop- mandibular incisive canal, and lingual foramina and their
erative lateral cephalograms showed a statistically significant neurovascular contents. Potential risks of interference may
change in the vertical position of the inferior vermilion border result in neurosensory disturbances and/or hemorrhage
increasing relative to the occlusal plane from 9.7 to 11.0 mm (Mraiwa et al. 2003). The anterior mandible is also a com-
resulting also in more exposure of the lower incisor teeth aug- mon site of mandibular bone fractures, mainly located in the
menting from 1.9 to 3.6 mm. However, according to the parasymphyseal regions (Goodday 2013).
authors, these changes were not directly related to the harvest- Many clinicians consider the placement of dental
ing procedure but rather to a failure in correctly repositioning implants in the (edentulous) anterior mandible a relatively
the mentalis muscles leading to a labial ptosis condition. low-risk procedure (Miller et al. 2011). However, such
A rare complication of bone block harvesting from the assumption is deceptive, and without proper training and
chin was reported by Cordaro et al. (2004). While the lingual treatment planning, severe and sometimes even life-threat-
cortex appeared to be intact at the time of surgery, a CT scan ening complications may occur (Chap. 22). The introduc-
taken 6 months later demonstrated a fractured and lingually tion of CBCT scanning allows visualization, routine
displaced fragment of lingual bone, probably due to the trac- examination, and documentation of nearby anatomical
tion of the genioglossus and geniohyoid muscles. The patient structures.
reported neither pain nor functional impairment, and no Due to the powerful bilateral mentalis muscles, there is
treatment was provided. a certain risk for wound dehiscence when using submar-
ginal or mucosal incisions for flap elevation in the anterior
mandible (Figs. 20.23 and 20.24). The clinician is advised
Clinical Relevance of the Anterior Mandible to pay attention to the flap design and the incision sites
but also to accomplish tension-free primary wound
Since the anterior mandible is a frequent area of surgical closure.
interventions, such as implant placement, bone harvesting,
or genioplasties, consideration and precise radiographic
Fig. 20.23 Slight wound dehiscence 10 days after block harvesting in Fig. 20.24 Marked wound dehiscence 7 days after apical surgery of all
the anterior mandible of a 27-year-old male four mandibular incisors in a 60-year-old male
442 20 Anterior Mandible
Yavuz MS, Buyukkurt MC, Tozoglu S, Dagsuyu IM, Kantarci Yonchak T, Reader A, Beck M, Meyers WJ. Anesthetic efficacy of uni-
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bone grafts by three-dimensional computed tomography. Dent innervation in anterior teeth. Oral Surg Oral Med Oral Pathol Oral
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Mandibular Incisive Canal
21
The mandibular incisive canal (Figs. 21.1, 21.2, and 21.3) is canal and its neurovascular bundle are rarely addressed in
the extension of the mandibular canal that continues beyond anatomical and surgical textbooks. It is even more interest-
the mental canal into the interforaminal region (Mraiwa et al. ing that the placement of dental implants in the interforami-
2003b). The latter region is defined as the anterior part of the nal region is considered a safe and low-risk procedure, and
mandible between both mental foramina. Since the mandibu- clinicians new to implant dentistry are encouraged to per-
lar incisive canal carries sensory fibers to the anterior teeth form their first implant surgeries in the anterior mandible.
via the mandibular incisive nerve, any damage to these struc- In fact, modern dental implantology has the longest docu-
tures results in temporary or permanent sensory loss in the mentation of implants inserted in the interforaminal region to
anterior teeth. support ball- or bar-retained overdentures. Also the concept
Surgical interventions in the anterior mandible are fre- of implant-borne, full-arch fixed dentures was first intro-
quent and include placement of dental implants, genioplasty, duced in the anterior mandible. Although this area appears to
and bone harvesting from the symphysis, as well as other be a safe zone for implant placement, case reports describing
types of oral surgery such as apical surgery, removal of teeth, sensory loss or perforation of the lingual plate with life-
root fragments or bone lesions, and bone fracture repair with threatening hemorrhage following implant bed preparation
osteosynthesis techniques. Although surgery is often per- demand careful reconsideration of anterior mandibular anat-
formed in the anterior mandible, the mandibular incisive omy (Abarca et al. 2006).
MC
MIC MeF
MIC
Chin
Buccal Lingual
Fig. 21.1 Reformatted sagittal CBCT image of the left mandible
showing the mandibular incisive canal in a 68-year-old female. MeF
mental foramen, MC mandibular canal, MIC mandibular incisive canal
Fig. 21.2 The sagittal CBCT image at the level of the implant in the
left canine position demonstrates the relatively buccal position of the
mandibular incisive canal. MIC mandibular incisive canal
Chin
MIC MIC
MeF MeF
* GT
Fig. 21.3 Both mandibular incisive canals are clearly visible on the
axial CBCT image. GT genial tubercle, MeF mental foramen, MIC
mandibular incisive canal, * apical part of dental implant
Presence of the Mandibular Incisive Canal 447
Presence of the Mandibular Incisive Canal labyrinth of intertrabecular spaces containing neurovascular
bundles that may diminish observational effectiveness
The frequency of a mandibular incisive canal shows large (Polland et al. 2001).
variations among the applied methods of evaluation but also A recent dissection study of 40 Chinese cadaveric man-
within a specific method (Table 21.1). Macroscopic anatomi- dibles demonstrated that the wall of the mandibular incisive
cal dissection of cadavers in three studies reported complete canal was formed in 80 % of the cases by a very thin layer of
expression of the mandibular incisive canal in all individuals compact bone or partially by spongy bone. The remaining
(Mardinger et al. 2000; de Andrade et al. 2001; Uchida et al. 20 % of the specimens displayed a canal coursing through
2007) while presence of this canal was reported to be 96 % in spongy bone only (Xu et al. 2015). Thus, indistinct wall mor-
another study (Mraiwa et al. 2003a). A survey evaluating the phology may result in limited spatial and contrast resolution
presence of the canal with regard to the dental status found a hindering visibility of the canal as it narrows and approaches
mandibular incisive canal in 92 % of dentate subjects but the midline (Apostolakis and Brown 2013).
only in 31 % of edentulous mandibles (Obradovic et al. The mandibular incisive canal displays bilateral conti-
1993). The radiographic visibility of the mandibular incisive nuity in some cases. Wang et al. (2001) presented a case
canal is largely dependent on the imaging technique utilized report of mandibular incisive canals that appeared to be
for assessment (Figs. 21.4 and 21.5). Conventional radiogra- bilaterally continuous based on periapical radiographs. As
phy displayed limited capability in visualization of the canal the canals coursed in a steep upward trajectory toward the
based on a comparative study utilizing periapical radiographs midline, two horizontal anastomoses were observed in the
taken from cadaveric specimens (Mardinger et al. 2000). In interdental areas between lateral and central incisors sug-
this study, the mandibular incisive canal was observed in gesting cross-innervation. Similar anastomoses between
only 56 % of cases that were confirmed to possess a canal right and left mandibular incisive canals were reported in a
based on subsequent anatomical dissection. However, the MRI study of 64 patients (Krasny et al. 2012a). An anasto-
same authors showed a statistically significant correlation mosis in the symphyseal region was observed in 70 % of the
between the anatomic structure of the canal borders (com- patients (plexus-like in 26 %). The same authors reported in
plete, partial, or no cortical border) and its radiographic another MRI study that a double unilateral mandibular inci-
detectability in periapical radiographs. sive canal was seen in 6.3 % of cases (Krasny et al. 2012b).
In a survey comparing panoramic radiographs with Some authors have reported the use of immersion endos-
CBCT, the canal was visualized in 83.1 % of cases utilizing copy for intraoperative visualization of the mandibular inci-
CBCT compared to only 11.2 % occurrence based on pan- sive nerve (Beltran et al. 2011; Cantin et al. 2012). Jacobs
oramic radiographs (Pires et al. 2012). In general, CT (93 %) et al. (2007) utilized high-resolution magnetic resonance
and CBCT (49.5–100 %) demonstrated effective identifica- imaging to study the content of the mandibular incisive
tion of the canal, but good visibility of the canal was limited canal. Their observations indicated that the canal contained a
to only 7.5–39.6 % of the cases (Jacobs et al. 2002; Parnia true neurovascular bundle with nerve structures with a sen-
et al. 2012). The incisive mandibular canal can occur as a sory modality.
448 21 Mandibular Incisive Canal
MeF MeF
MC
MC
MIC MIC
Fig. 21.4 Section of a panoramic radiograph showing bilateral mandibular incisive canals in a 61-year-old male. MC mandibular canal, MeF
mental foramen, MIC mandibular incisive canal
Length and Diameter of the Mandibular Incisive Canal 449
Length of
Author(s) Study material N MIC Diameter of MIC at specific sites
At origin of canal In premolar area In canine area In incisor area Site not specified
Bavitz et al. (1993) 24 cadavers (anatomical 47 – – 1.3 ± 0.4 (0.5–2) – – –
dissection) at 2 mm mesial to
MF
Mardinger et al. 20 cadaveric mandibles 46 – Dissection: Dissection: Dissection: Dissection: –
(2000) and 6 hemimandibles 2.09 ± 0.42 (1–2.9) 1.69 ± 0.38 (1.2–2.8) 1.25 ± 0.24 (0.7–1.7) 0.98 ± 0.22 (0.5–1.5)
(periapical radiographs Radiograph: Radiograph: Radiograph: N/A Radiograph: N/A
and anatomical 2.14 ± 0.73 (0.9–3.4) 1.73 ± 0.4 (0.7–2.1)
dissection)
de Andrade et al. 12 human mandibles 23 Right: – – – – –
(2001) (anatomical dissection) 20.6 ± 2.99
Left:
1.5 ± 2.06
Jacobs et al. (2002) 230 patients (CT) 460 – – – – – 1.1 ± 0.3 (0.5–2.3)
(mean age 55 years,
range 18–80 years)
Mraiwa et al. 50 dry mandibles 100 – – – – – 1.8 ± 0.5 (0.6–3.4)
(2003a) (anatomical dissection)
Uchida et al. (2007) 38 cadavers (anatomical 75 – 3.1 ± 1.2 (1–6.6) – – – At 3 mm:
dissection) 2.0 ± 1.0 (0.5–6)
At 5 mm:
1.7 ± 0.8 (0.5–4.9)
Uchida et al. (2009) 4 cadavers (CBCT and 7 – CBCT: 2.2 ± 0.4 – – – –
anatomical dissection) Anatomical
dissection: 2.2 ± 0.4
71 cadavers (anatomical 140 – 2.8 ± 1.0 (1.0–6.6) – – – –
dissection)
Makris et al. (2010) 100 patients (CBCT) 200 15.1 ± 5.68 – – – – –
(mean age 54.9 years,
range 10–80 years)
Krasny et al. 64 patients with MRI 58 right side Right: – – – – –
(2012a) (mean age 43.7 years, 57 left side 20.7 ± 3.6
range 15–76 years) Left:
21.0 ± 3.3
Parnia et al. (2012) 96 patients (CBCT) 192 – – – – – 1.47 ± 0.5
(mean age 46.6 years, Right: 1.49 ± 0.7
range 20–77 years) Left: 1.44 ± 0.48
(measured at 4
points each 2 mm
apart)
21 Mandibular Incisive Canal
Pires et al. (2012) 89 patients (panoramic 89 All: 7 ± 3.8 – – – – 0.4 × 0.4–4.6 × 3.2
radiography and CBCT) Right:
(mean age 7.1 ± 4.0
59 ± 14.9 years) Left: 6.6 ± 3.7
Romanos et al. 1045 patients 28 10.7 ± 4.95 – – – – 1.48 ± 0.57
(2012) (panoramic
radiography) (mean age
37 years, range 18–65
years)
Apostolakis and 102 patients (CBCT) 204 All: – 1.4 (0.4–2.4) 1.2 (0.4–2.2) 0.95 (0.3–1.9) –
Brown (2013) (mean age 53 years, 8.9 ± 5.83
range 20–89 years) (0–24.6)
Right: 9 ± 6.1
(0–23.3)
Left: 8.8 ± 5.6
(0–24.6)
Borges Rosa et al. 326 patients (CBCT) 652 9.11 ± 3.00 – – – – 1.48 ± 0.66
Length and Diameter of the Mandibular Incisive Canal
Distances from the Mandibular Incisive while others have found a linear (Pires et al. 2012) or an
Canal to Adjacent Structures upward direction of the canal (Pommer et al. 2008).
With regard to the distance between the buccal bone plate
From a surgical perspective, an understanding of the precise and the canal, it increased from the lateral to the central areas
location of the mandibular incisive canal with respect to con- in all surveys that recorded measurements at several sites
tiguous structures is absolutely necessary to avoid damage to (Pommer et al. 2008; Makris et al. 2010; Pires et al. 2012;
the canal and its neurovascular content (Figs. 21.6, 21.7, Apostolakis and Brown 2013). The values ranged from 1.9 to
21.8, 21.9, and 21.10). The mean distance between the canal 4.8 mm with the greatest distance measured in the incisor
and the adjacent root tips ranges between 4.6 and 12.18 mm area. These data indicate a lingual direction of the mandibu-
depending on the tooth, but it is usually greatest among the lar incisive canal within the anterior mandibular body.
incisors since these teeth possess the shortest roots (de The mean distance between the mandibular incisive canal
Andrade et al. 2001; Pommer et al. 2008; Pires et al. 2012; and the lingual bone plate was more consistent compared to
Apostolakis and Brown 2013) (Table 21.3). the distance relative to the buccal bone plate and ranged from
The mean distance between the canal and the lower bor- 4.4 to 6.43 mm (Makris et al. 2010; Parnia et al. 2012; Pires
der of the mandible is 7.2–14 mm, again with variations et al. 2012; Apostolakis and Brown 2013; Vu et al. 2015).
depending on the site of measurement along the canal. Some Overall, the canal was located closer to the bony buccal plate
authors have reported increasing values toward the midline compared to the lingual aspect, and the clinician is advised to
indicating a downward course of the canal (Mraiwa et al. exercise caution when performing an osteotomy in the ves-
2003a; Makris et al. 2010; Apostolakis and Brown 2013), tibular aspect of the anterior mandible (see below).
4 2
Fig. 21.6 Mean values reported in the literature for distances from
the mandibular incisive canal to the adjacent anatomical structures. 1
root apices, 4.6–10.9 mm; 2 surface of buccal plate, 1.9–4.8 mm; 3
inferior mandibular border, 7.2–14 mm; 4 surface of lingual plate,
4.4–5.7 mm
Distances from the Mandibular Incisive Canal to Adjacent Structures 453
MIC
Chin
GT
MeF
MIC
PM1
C
Fig. 21.9 Buccolingual CBCT section at the level of the right man-
dibular canine. MIC mandibular incisive canal
MC
MeF MIC
MIC
MeF
Fig. 21.8 Reformatted coronal-sagittal view along the course of the
right mandibular incisive canal showing an ascending bone canal MIC
(arrowheads) between the canine and the first premolar. C canine, MC MIC
mandibular canal, MeF mental foramen, MIC mandibular incisive
canal, PM1 first premolar
Course of the Mandibular Incisive Canal dible 6 mm mesial to the mental foramen in 85 % of the
cases and 12 mm mesial to the mental foramen in 60 % of
In a study evaluating 326 patients with CBCT, the canal cases (Makris et al. 2010). The data of the same authors
showed a downward path in 51.3 %, a linear path in 38.3 %, showed that the canal was directed slightly down- and
and an upward path in 10.4 % (Borges Rosa et al. 2013). inward as it approached the midline of the mandible. An
When the course of the canal was assessed with respect to extraosseous course of the mandibular incisive canal was
the buccolingual dimension, a lingual path was followed in recently reported (de Souza et al. 2013). In a 49-year-old
71.6 % and a buccal path in 28.9 %. With regard to the buc- female patient, the canal had a normal trajectory for 4 mm
colingual location of the mandibular incisive canal, it was beyond the mental foramen but extended to the buccal cor-
predominantly found in the buccal part of the anterior man- tex in the canine area and exteriorized.
Table 21.3 Distances (mm) from mandibular incisive canal (MIC) to adjacent anatomical structures
Distance from MIC Distance from Distance from
Distance from MIC to inferior MIC to buccal MIC to lingual
Author(s) Study material N to root tip mandibular border bone plate bone plate
Bavitz et al. (1993) 24 cadavers 47 – – 1.9 mm ±0.7 –
(anatomical (0–3 mm) at
dissection) 2 mm mesial to
MF
de Andrade et al. 12 human mandibles 23 Right canine: Right side: Right side: –
(2001) (anatomical 5.7 ± 2.76 10.8 ± 2.45 2.7 ± 0.65
dissection) Left canine: Left side: Left side:
6.1 ± 2.02 10.4 ± 1.62 (sites 2.6 ± 0.67 (sites
Right lateral not specified) not specified)
incisor: 7.4 ± 3.69
Left lateral incisor:
8.0 ± 3.33
Jacobs et al (2002) 230 patients (CT) 460 – 7.6 ± 2.2 (2.2–15.9) – –
(mean age 55 years, (sites not specified)
range 18–80 years)
Mraiwa et al. 50 cadavers 100 – Canine: 9.7 ± 1.8 – –
(2003a) Lateral incisor:
7.2 ± 2.1
Pommer et al. 50 patients (CT) 100 First premolar: First premolar: First premolar: –
(2008) (mean age 5.6 ± 2.4 10.7 ± 1.9 3.4 ± 1.1
47.2 years, range Canine: 5.2 ± 2.4 Canine: 10.3 ± 2.2 Canine: 4.2 ± 1.5
25–71 years) Lateral incisor: Lateral incisor: Lateral incisor:
6.6 ± 2.4 11.1 ± 2.5 4.2 ± 1.5
Central incisor: Central incisor: Central incisor:
5.3 ± 2.2 14.0 ± 2.8 4.4 ± 1.4
Makris et al. 100 patients (CBCT) 200 – At 6 mm mesial to At 6 mm mesial At 6 mm mesial
(2010) (mean age MF: 11.2 ± 1.76 to MF: 3.6 ± 1.03 to MF: 5.7 ± 1.7
54.9 years, range At 12 mm mesial to At 12 mm mesial At 12 mm mesial
10–80 years) MF: 9.5 ± 1.6 to MF: 4.7 ± 1.7 to MF: 5.3 ± 1.6
Parnia et al. (2012) 96 patients (CBCT) 192 – All: 8.7 ± 1.43 All: 3.5 ± 1.17 All: 4.5 ± 1.4
(mean age Right: 8.9 ± 1.68 Right: 3.4 ± 1.26 Right: 4.6 ± 1.51
46.6 years, range Left: 8.6 ± 1.51 Left: 3.5 ± 1.25 Left: 4.4 ± 1.51
20–77 years) (measured at 4 (measured at 4 (measured at 4
points each 2 mm points each 2 mm points each 2 mm
apart) apart) apart)
Pires et al. (2012) 89 patients 178 At origin: 4.6 ± 2.2 All: 10.2 ± 2.4 At origin: At origin:
(panoramic At terminal portion: At origin: 10.4 ± 2.3 2.2 ± 1.1 4.7 ± 2.1
radiography and 6.1 ± 3.1 At terminal portion: At terminal At terminal
CBCT) (mean age 10.1 ± 2.5 portion: 3.3 ± 1.7 portion: 5.2 ± 2
59 ± 14.9 years)
Course of the Mandibular Incisive Canal 455
Mandibular Incisive Nerve anterior mandible may also produce pressure on the mental
nerve, causing numbness of the mucocutaneous areas
The mandibular incisive nerve is one of the two terminal (Mardinger et al. 2000).
branches of the inferior alveolar nerve (Fig. 21.11). The The fact that the incisive canal terminates at the level of
mandibular incisive nerve, also called incisive bundle or the lateral incisors might partially explain the ongoing discus-
incisive plexus, supplies sensory innervation to the ipsilat- sion concerning the neurovascular supply of the incisor teeth
eral first premolar, canine, lateral, and central incisors. This (Jacobs et al. 2002). Pogrel et al. (1997) demonstrated in ten
nerve may course forward from its ramification where the cadaveric heads that branches of the mental nerve reentered
mental nerve branches from the inferior alveolar nerve, in a the labial plate to supply the lower incisors in 15 % of the
well-defined corticalized bone canal or in loose, trabecular specimens supporting the concept of crossover innervation
spongy bone. The mandibular incisive nerve may be dam- from the contralateral mental nerve. Histologically, the neu-
aged by direct trauma during an osteotomy or by hematoma rovascular bundle of the mandibular incisive canal was
formation following osteotomy or bone injury. A hematoma described as a nerve consisting of fascicles of myelinated
spreading in a posterior direction within the mandibular nerve fibers surrounded by perineurium and a distinct epineu-
incisive canal or within the cancellous compartment of the rium with accompanying blood vessels (Jacobs et al. 2007).
MIN IAN
MeN
IAN
Clinical Relevance of the Mandibular Incisive Kütük et al. (2013) retrospectively evaluated ten patients
Canal and Nerve with neuropathic pain following placement of a total of 19
implants in the anterior mandible. None of the patients had
According to Rosenquist (1996) two complications may dysesthesia or paresthesia but patients complained of burn-
occur when an implant is placed in contact with the man- ing, tingling, or throbbing pain. CBCT scans showed that 15
dibular incisive canal (Figs. 21.12, 21.13, 21.14, 21.15, and implants had perforated the mandibular incisive canal, and
21.16). First, the implant may fail to integrate due to the four implants were less than 1 mm from the canal. In 30 % of
migration of soft tissue around the implant, as seen when the cases, the neuropathy was permanent. Lee et al. (2012)
implants are placed in contact with the nerve of the nasopala- presented a case with brisk, pulsatile bleeding from the man-
tine canal in the maxilla. Second, edema of the epineurium dibular incisive canal during implant surgery in the anterior
caused by trauma to the anterior nerve plexus may spread to mandible.
the ramification resulting in neurosensory dysfunction of the Considerably more sensory deficits have been reported
main branch of the nerve. after bone harvesting from the chin area of the mandible
Kohavi and Bar-Ziv (1996) reported a patient complaining compared to other intraoral bone donor sites (von Arx 2009).
of severe pain after placement of two implants in the lateral Since the procedure of chin bone harvesting usually involves
incisor areas of the mandible. Cross-sectional CT images the removal of large bone blocks, the mandibular incisive
revealed that implants perforated (right side) and contacted nerve is likely to be damaged with subsequent sensitivity
(left side) the mandibular incisive canal. The implants were changes in the anterior teeth (von Arx et al. 2005, 2007).
subsequently removed and the patient reported 6 months later Recent articles (Pommer et al. 2008; Apostolakis and Brown
some improvement of the altered sensation. Liang et al. (2008) 2013) have shown that general recommendations of safety
described a severe case of permanent pain and sensitivity margins concerning symphyseal bone harvesting appear to
change on the right side following placement of four 15-mm be unreliable due to the large variations in the dimensions
long interforaminal implants. Postsurgical radiography and course of the mandibular incisive canal. The safest
showed overlap of the most distal right implant with the ante- approach appears to be an individual preoperative three-
rior loop, and both implants on the right side were subse- dimensional radiographic analysis of the donor site to avoid
quently removed and replaced with two shorter 10-mm postsurgical neurological complications.
implants. However, the pain did not subside and CBCT images The detailed analysis of 50 cases with CT by Pommer
showed the distal implant was in contact with the mandibular et al. (2008) showed that observing safety margins of 5 mm
incisive canal. would endanger the content of the mandibular incisive canal
Romanos and Greenstein (2009) described an edentulous in 57 % of the evaluated cases. Applying new safety margins
case utilizing four dental implants in the anterior mandible. including a maximum harvest depth of 4 mm and at least
The preoperative CT and panoramic radiograph showed a 8 mm below the root apices of the adjacent teeth may mark-
3-mm-wide mandibular incisive canal extending toward the edly reduce the risk of altered postoperative tooth sensitivity
midline on the right side. Upon preparation of the implant bed (Pommer et al. 2008). By extending the distance from 5 to
in the right canine site, the patient experienced substantial pain 8 mm between the tooth apices and the upper bone cut of the
and bleeding. No implant was placed and a collagen sponge harvest site, nerve damage can be avoided in over 75 % of
was applied for hemorrhage control. Healing was uneventful, cases regardless of the depth of the harvest defect (Pommer
and no sensory disturbances of the lip or mucosa were reported. et al. 2008). The symphysis was found to be a safe donor site
Considering the few neurological complications described in 56 % of the evaluated patients to harvest a graft of 10 mm
in the literature comparing numerous implants inserted in the diameter and in 90 % for a graft of 6 mm diameter (Pommer
anterior mandible, the risk of traumatic nerve injury appears et al. 2008). The remaining 10 % of cases were not suitable
to be minimal (Walton 2000). In edentulous subjects, the for chin bone harvesting. Regarding the depth of bone blocks,
mandibular incisive canal may still be present, though thin- the same authors also recommended leaving the lingual cor-
ner and shorter, but its neurovascular content may have tex intact (monocortical graft) to reduce the risk of bleeding
degenerated as a consequence of tooth loss, explaining the in the anterior floor of the mouth (Chap. 22). If a maximum
very low hazard of neural damage observed in this area. of 4 mm is not exceeded, neural damage may be avoided in
However, Jacobs et al. (2002) noted that nerve degeneration almost half of the patients (irrespective of the distance from
may be delayed following tooth loss and a time delay should the apices). Since the thickness of the cortical bone measures
be applied prior to canal evaluation to account for this dis- on average 2 mm in that area (Park et al. 2004), a bone block
crepancy. They also commented that as long as the influence of 4-mm depth ideally would consist half of the cortical bone
of edentulism on the appearance of the mandibular incisive that ensures volume stability and half of the cancellous bone
canal remained unresolved, any surgical procedure might that favors integration of bone graft and promotes new bone
traumatize the neurovascular incisive bundle. formation (Pommer et al. 2008).
458 21 Mandibular Incisive Canal
MeF
MIC
MIC
MIC
MIC
MeF
MeF
MC
GT
MIC Fig. 21.14 Axial CBCT image showing bilateral mandibular incisive
canals in a 59-year-old female scheduled for implant placement in the
anterior mandible. GT genial tubercle, MC mandibular canal, MeF
mental foramen, MIC mandibular incisive canal
Fig. 21.13 The coronal view of the posterior implant demonstrates the
proximity of the implant tip to the mandibular incisive canal. MIC man-
dibular incisive canal
Clinical Relevance of the Mandibular Incisive Canal and Nerve 459
AC MIC
Fig. 21.15 The coronal CBCT image demonstrates the close position
of the mandibular incisive canal to the alveolar crest. AC alveolar crest,
MIC mandibular incisive canal
MIC
MeF
MeF
interforaminal region: a second attempt introducing cone beam Vu DD, Brockhoff HC, Yates DM, Finn R, Phillips C. Course of the
computed tomography. J Oral Maxillofac Surg. 2009;67:744–50. mandibular incisive canal and its impact on harvesting symphysis
von Arx T, Häfliger J, Chappuis V. Neurosensory disturbances follow- bone grafts. J Oral Maxillofac Surg. 2015;73:258e1–12.
ing bone harvesting in the symphysis. A prospective clinical study. Walton JN. Altered sensation associated with implants in the anterior
Clin Oral Implants Res. 2005;16:432–9. mandible: a prospective study. J Prosthet Dent. 2000;83:443–9.
von Arx T, Chappuis V, Kälin C, Bornstein MM. Laser Doppler flowm- Wang PD, Serman NJ, Kaufman E. Continuous radiographic visualiza-
etry for assessment of anterior mandibular teeth in conjunction with tion of the mandibular nutrient canals. Dentomaxillofac Radiol.
bone harvesting in the symphysis: a clinical pilot study. Int J Oral 2001;30:131–2.
Maxillofac Implants. 2007;22:383–9. Xu Y, Suo N, Tian X, Li F, Zhong G, Liu X, Bao Y, Song T, Tian
von Arx T. Intraoral bone harvesting. In: Buser D, editor. 20 years H. Anatomic study on mental canal and incisive nerve canal in inter-
of guided bone regeneration. Chicago: Quintessence; 2009. foraminal region in Chinese population. Surg Radiol Anat.
p. 97–121. 2015;37:585–9.
Lingual Foramina and Canals
22
Lingual foramina (Figs. 22.1, 22.2, 22.3, and 22.4) have not (or midline) lingual foramina (MLF) are located precisely at
attracted great interest in anatomical text except the lingual the anatomical midline of the lingual aspect of the mandible
foramina located in the midline of the mandible. With the close to the genial tubercles (Figs. 22.6, 22.7, 22.8, 22.9,
introduction and wider accessibility of three-dimensional radi- 22.10, and 22.11). Lingual foramina located up to the poste-
ography, lingual foramina other than the midline type have rior margin of the canine are referred to as paramedian lingual
been documented and studied. Several case reports of severe foramina, while positioned distal to the canine are called pos-
and near-fatal hemorrhage in the floor of the mouth following terior lingual foramina (von Arx et al. 2011). Many authors
implant placement in the mandible have contributed to the denote all lingual foramina that are not located in the midline
evaluation of lingual areas of the mandible, thus confirming as lateral lingual foramina (LLF) (Figs. 22.12, 22.13, 22.14,
the importance of these small anatomical structures. 22.15, 22.16, and 22.17). The presence of a MLF is a frequent
Lingual foramina are mainly classified based on their loca- finding irrespective of the applied study method, whereas
tion on the inner aspect of the mandible (Fig. 22.5). Median LLF occurrence is much less by comparison (Table 22.1).
LLF LLF
MLFsu
GT
GT GT
Fig. 22.2 Occlusal view of the anterior mandible showing lateral lin-
gual foramina located between the central and lateral incisors in the
crestal area. GT genial tubercle, LLF lateral lingual foramen
MLFin
GT
LLF
MLF
MLFsu
GT
MLFin
Fig. 22.6 Sagittal CBCT cut through the midline of the mandible
showing two median lingual foramina and corresponding canals supe-
rior and inferior to the genial tubercle in a 69-year-old female. GT
genial tubercle, MLFin inferior median lingual foramen, MLFsu supe-
rior median lingual foramen
22 Lingual Foramina and Canals 465
MLCsu
MLCsu
MLCmi
MLCin
MLCin Fig. 22.9 The coronal CBCT image demonstrates three median lingual
canals. MLCin inferior median lingual canal, MLCmi middle median
lingual canal, MLCsu superior median lingual canal
Fig. 22.7 The coronal CBCT image exhibits two median lingual
canals surrounded by relatively compact bone. MLCin inferior median
lingual canal, MLCsu superior median lingual canal
MLFsu
MLFmi
MLFin
GT
MLFmi
MLFin
Fig. 22.8 Three median lingual foramina and corresponding canals are
visible in the sagittal CBCT image of a 19-year-old male. GT genial
tubercle, MLFin inferior median lingual foramen, MLFmi middle
median lingual foramen, MLFsu superior median lingual foramen
466 22 Lingual Foramina and Canals
LI
LLF
LLC
MLFsu
MLFmi
MLFin
Fig. 22.11 The midline sagittal CBCT section shows three lingual Fig. 22.13 The sagittal CBCT image through the upper right lateral
canals originating from three median lingual foramina. MLFin inferior lingual foramen demonstrates the close relationship of its descending
median lingual foramen, MLFmi middle median lingual foramen, canal to the root of the lower right mandibular incisor. LI lateral incisor,
MLFsu superior median lingual foramen LLC lateral lingual canal, LLF lateral lingual foramen
LLF LLF
MLF
GT
LLF LLF
PM1
PM1
Root
MHR
remnant
MHR
LLF LLF
LLF
SMF
LLF
Fig. 22.15 The sagittal CBCT view demonstrates the two inferiorly
Fig. 22.14 A 3D rendering of CBCT images of the lower left mandible located lingual foramina and a root remnant. LLF lateral lingual fora-
presenting two lateral lingual foramina located in the inferior portion of men, PM1 first premolar
the mandible in a 67-year-old male. LLF lateral lingual foramen, MHR
mylohyoid ridge, PM1 first premolar, SMF submandibular fossa
PM 1
MHR
SMF
LLF
LLF
Fig. 22.17 The coronal CBCT image at the level of the missing second
molar shows the more posterior of the two lateral lingual foramina and
its canal (note the lingual undercut). LLF lateral lingual foramen, MHR
mylohyoid ridge, SMF submandibular fossa
Fig. 22.16 The coronal CBCT image at the level of the first premolar
shows the more anterior of the two lateral lingual foramina and its canal
located close to the lower mandibular border. LLF lateral lingual fora-
men, PM1 first premolar
Table 22.1 Frequency and location of lingual foramina (LF)
468
Tagaya et al. (2009) 200 patients (CT) (mean age 54.9 years, range 200 patients 100 % (95 % had a MLF above, 49.5 % 80 % (36 % unilateral –
24–86) 400 sides at and 57 % below the mental spine) 44 % bilateral)
Makris et al. (2010) 100 patients (CBCT) (mean age 54.9 years, 100 patients 81 % (82.7 % superior and 17.3 % – –
range 10–80 years) inferior position)
Naitoh et al. (2010) 28 patients (mean age 54.5 years, range 21–74 56 sides (CT) 98.2 %* 50 % (sides)* *Refer to lingual bony canals
years) 56 sides (CBCT) 100 %* (47.3 % superior, 40 % 50 % (sides)* *Refer to lingual bony canals
inferior, 12.7 % close to mandibular
border)
Lingual Foramina and Canals
22
Author(s) Study material N Median LF (MLF) Lateral LF (LLF) Comments
Scaravilli et al. (2010) 114 patients (CT) (mean age 44.7 years, range 114 patients 90.4 % – –
13–75 years)
Babiuc et al. (2011) 36 patients (CBCT) (mean age 46 years, range 36 sites 100 % – –
25–70 years)
von Arx et al. (2011) 179 patients (CBCT) (mean age 42.7 years, 1054 sites 96.2 % 9.7 % (paramedian) –
range 11–87 years) 14.2 % (posterior)
Jalili et al (2012) 412 patients (panoramic radiography) (age 412 patients 6.1 % – –
range 7–78 years)
Parnia et al. (2012) 96 patients (CBCT) (mean age 46.6 years, 96 patients 49 % (29.2 % good visibility) – –
range 20–77 years)
Lingual Foramina and Canals
Przystanska and Bruska 397 dry mandibles 299 adult Superior MLF *Adults: 44 % (sides) *Authors used the term
(2012) mandibles Adults: 86 % Children: 28 % (sides) “accessory foramen lateral to
18 child Children: 78 % Fetuses: 17.5 % (sides) genial tubercle”
mandibles Fetuses: 31 %
80 fetus Inferior MLF:
mandibles Adults: 60 %
Children: 50 %
Fetuses: 11 %
Romanos et al. (2012b) 299 patients (CBCT) (mean age 45.4 years, 299 patients 47.5 %* 38.8 %* *Authors assessed bony
range 13–93 years) lingual canals rather than
foramina up to the first
premolar area
Sheikhi et al. (2012) 102 patients (CBCT) (mean age 52.4 years, 102 patients 100 % – –
range 21–91 years)
Choi et al. (2013) 20 human (Korean) cadaveric mandibles 20 mandibles 100 % 50 % –
(micro-CT)
Cantekin et al. (2014) 100 children and adolescents (mean age 100 panoramic 61 % (good visibility in 6 %) – –
12.3 ± 3.7 years) radiographs
100 CBCT 100 % (good visibility in 45 %) – –
Kilic et al. (2014) 200 patients (CT) (mean age 53.2 years) 200 patients 96.5 % Right side: 35 % –
Left side: 34 %
Sahman et al. (2014) 500 patients (CBCT) (mean age 500 patients – 24.8 %* *Lateral lingual canals
41.2 ± 15 years, range 20–84 years)
Sekerci et al. (2014) 500 patients (CBCT) (mean age 500 patients 95.2 % – Only LF included ≥0.25 mm
30.3 ± 12.5 years, range 19–64 years)
469
470 22 Lingual Foramina and Canals
Frequency and Location of the Lingual cases (Tepper et al. 2001). A slightly higher frequency of 44 %
Foramina for bilateral LLF was reported in CT images of 200 patients
(Tagaya et al. 2009). However, no information was provided in
The most frequently evaluated lingual foramina are the MLF both studies when the LLF were symmetrically located.
with many cadaver and dry mandible studies showing that it Krenkel et al. (1985) specifically evaluated lingual foram-
is a highly consistent finding (Table 22.1). The MLF can ina located in the crestal portion of 100 macerated and den-
often be differentiated into a superior, middle, and inferior tate mandibles. These foramina were found between the
lingual foramen depending on their vertical location in rela- central and lateral incisors in 81 % of right sides and in 83 %
tion to the bilateral superior and inferior mental spines or of left sides. The LLF was also found between the lateral
collectively known as the genial tubercles (Fig. 22.18). incisors and canines (6–14 %) and between the canines and
Accordingly, these foramina are called supraspinous, inter- first premolars (8–12 %). The authors concluded that the
spinous, and infraspinous foramina. Normally, the number of location of these lingual foramina in the immediate vicinity
MLF ranges from one to three, but some authors have of tooth sockets and close to the alveolar crest makes them a
described up to four median lingual foramina (Katakami severe hazard of damaging the entering arterial branches.
et al. 2009; Choi et al. 2013). The majority of studies describe A different approach to assess lingual foramina irrespective
two MLF as the most common finding (Table 22.2). If only a of size, called “accessory foramina on the medial mandibular
single median lingual foramen is present, it is usually located surface,” was conducted in 80 dry human mandibles by
superior to the mental spine. In mandibles having two foram- Fanibunda and Matthews (2000). Evaluation was carried out
ina, the larger was located above the genial tubercles. The using a microscope (magnification 9–20×). The authors con-
majority of mandibles (15/16) with three MLF showed two sidered only those foramina that showed a communication
of the three foramina located below the genial tubercles with the underlying cancellous bone determined by shining a
(Rosano et al. 2009). light from an optical fiber through the foramen or by passing a
LLF have been evaluated less frequently than MLF, and human hair through it. The median number of lingual foram-
they have also been observed in fewer cadaver and patient ina per mandible was 55 (range 22–494). The medial facing
mandibles. The LLF frequency generally reported in the lit- wall of the mandibular foramen was the commonest dedicated
erature ranges between 6 and 80 % (Table 22.1). Two CBCT site (98.3 %) followed by foramina on either side of the genial
studies have assessed the location of LLF with regard to tooth tubercles (71.9 %), the digastric fossa (71.9 %), and the mid-
sectors (thus, 16 sectors). Katakami et al. 2009 observed rela- line foramen above the genial tubercles (64 %). Given the dif-
tively high frequencies of LLF in the first premolar area ferent methodology of this study, the results cannot be
(36 %) but also in the central incisor area and canine field compared directly to the data presented in Table 22.1.
(each 19.4 %). None of the LLF was located above the man- Two studies evaluated MLF/LLF in prenatal mandibles.
dibular canal. In a similarly designed study, von Arx et al. In a study using CBCT, eight of nine fetal mandibles exhib-
(2011) described occurrences of 22.6 % and 20.3 % for LLF ited bilateral lingual foramina positioned adjacent with the
in the areas of the first and second premolars, respectively. deciduous canine crypt or just posterior to it (Shiozaki et al.
The high frequency of LLF below the first premolar was 2014). The lingual canals connected to the mandibular inci-
confirmed in a cadaver study in which 45.7 % of the sides of dry sive canal distributed to the frontal area or to the dental crypt
cadaveric skulls presented a significant lingual foramen in that close to the lingual foramen. Another study evaluated 397
region (Yoshida et al. 2005). Also Tagaya et al. (2009) reported dry mandibles (299 adults, 18 children, 80 fetuses) and found
that of 160 LLF observed in 200 patients with CT, 88 % were no significant differences in the distribution regarding loca-
positioned in the area lingual of the mental foramen, while the tion of midline and lateral lingual foramina (Przystanska and
remaining 12 % were located just mesial to the same area. Bruska 2012). However, lower occurrence was observed in
Regarding bilateral occurrence of LLF, a CT study with 70 fetal mandibles, in particular for midline lingual foramina,
patients demonstrated bilateral lingual canals in 29.7 % of the due to the incomplete ossification of the symphyseal region.
Frequency and Location of the Lingual Foramina 471
MLFsu
LLF
LLF
GT
GT
MLFmi
MLFin
Radiographic Detection of the Lingual Size and Distances of the Lingual Foramina
Foramina
The mean size of MLF reported in the literature irrespec-
In an experimental study of 15 dry mandibles examined with tive of their location with regard to the genial tubercles
periapical radiography and CT using wires to demarcate the ranges between 0.6 and 1.17 mm (Table 22.3). The small-
genial tubercles and the midline lingual foramen, it was dem- est diameter measured 0.1 mm and the largest 2.29 mm.
onstrated that the radiopaque region around the lingual fora- All studies evaluating the size of the superior and inferior
men is caused by the corticated walls of the canal originating MLF reported higher mean values for the superior MLF
from the midline lingual foramen and not related to the genial (0.75–1.12 mm) compared to the inferior MLF (0.58–
tubercles (Baldissera and Silveira 2002). The genial tubercles 0.9 mm). Only few studies have documented the size of
may produce a radiopacity without a definite form in the LLF that ranged between 0.59 and 1.23 mm. A CBCT
vicinity of the lingual foramen, but the characteristic radi- study measuring the horizontal and vertical size of MLF
opaque halo represents the dense bony walls of the lingual and LLF found that height was greater than the width
canal (McDonnell et al. 1994). When the radiographic tube is in MLF, while this ratio was reversed in LLF (von Arx
not oriented parallel to the long axis of the lingual canal, con- et al. 2011).
ventional radiographs usually fail to show the MLF. This may Regarding dimensions from MLF or LLF to adjacent
explain the difficulty of radiologic depiction of the bony canal anatomical structures, most studies have measured the dis-
using periapical radiographs (Vandewalle et al. 2006). tances to the lower border of the mandible (Table 22.4).
Cantekin et al. (2014) compared CBCT and panoramic radi- The mean distance from the superior MLF to the lower
ography in 100 children and adolescents (mean age 12.3 years) border of the mandible ranged between 12 and 18.4 mm.
for the detection of MFL. While CBCT images always showed The same distance for the inferior MLF ranged between
the lingual foramen, with good visibility in 45 %, the foramen 2.2 and 7 mm. Only two studies have assessed the distance
was only seen in 61 % of the panoramic radiographs, while good from the MLF to the alveolar crest since measurements
visibility was recorded in just 6 % of the cases. Naitoh et al. and comparisons are impeded by periodontal disease or
(2010) compared CBCT and multislice CT in the detection of bone atrophy. The mean distances from the superior MLF
lingual canals in 28 patients. The mean time lag between the to the alveolar crest measured 14.2 mm (Babiuc et al.
two radiographic modalities was 30.1 months (range 6.7– 2011) and 14.4 mm (Sheikhi et al. 2012). With respect to
58.8 months). A lateral lingual bony canal on 28 sides was LLF, mean distances to the lower border of the mandible
observed in both CBCT and CT images, whereas CBCT (n = 55) ranged from 5.3 to 11.5 mm. Differentiating between LLF
showed only one median lingual bony canal more than mul- located in the incisor/canine areas and in the premolar-
tislice CT (n = 54). The authors concluded that the depiction of molar areas, dimensions from the foramina to the lower
fine anatomic features of the mandible associated with neuro- mandibular border were 11.5 mm and 7.1 mm, respectively
vascular structures is consistent between CBCT and CT images. (von Arx et al. 2011).
Size and Distances of the Lingual Foramina 473
(continued)
Table 22.4 (continued)
476
von Arx et al. (2011) 179 patients (CBCT) (mean age 217 LF Distance from MLF to lower border of Distance from paramedian LLF to –
42.7 years, range 11–87 years) mandible: 10.0 ± 4.88 (1.3–17.3) lower border of mandible:
11.5 ± 8.19 (0.3–28.9)
Distance from posterior LLF to
lower border of mandible:
7.1 ± 4.20 (2.9–29.4)
Parnia et al. (2012) 96 patients (CBCT) (mean age NA Distance from MLF to lower border of – –
46.6 years, range 20–77 years) mandible: 8.9 ± 2.99
Przystanska and Bruska 299 dry adult mandibles 265 LF* – Distance from LLF to midline of *Authors used the term
(2012) mandible: “accessory foramen
Right side: 15.2 lateral to genial tubercle”
Left side: 15.4
Sheikhi et al. (2012) 102 patients (CBCT) (mean age 205 MLF Distance from superior MLF to lower – –
52.4 years, range 21–91 years) border of mandible: 14.1 ± 2.49
Distance from superior MLF to alveolar
crest: 14.4 ± 4.82
Distance from inferior MLF to lower
border of mandible: 4.27 ± 2.65
Distance from inferior MLF to alveolar
crest: 24.3 ± 5.0
Choi et al. (2013) 20 human (Korean) cadaveric 47 MLF Distance from superior MLF to lower – –
mandibles border of mandible: 12.7 ± 2.35 (9.0–17.2)
Distance from inferior MLF to lower
border of mandible: 6.5 ± 2.98 (1.5–11.7)
Kilic et al. (2014) 200 patients (CT) (mean age 236 MLF Distance from MLF to lower border of Distance from LLF to lower *Median values (not
53.2 years) 159 LLF mandible: *13.0 ± 4.29 (1–19) border of mandible: means)
Right side: *7.0 ± 4.06 (2–22)
Left side: *7.0 ± 5.49 (3–35)
Distance from LLF to midline:
Right side: 13.2 (median)
±6.25 (1.2–23)
Left side: 13.1 (median)
±NA (1.5–22.2)
Sekerci et al. (2014) 500 patients (CBCT) (mean age NA Distance from superior MLF to lower Distance from paramedian LLF to
30.3 ± 12.5 years, range 19–64 border of mandible: 18.4 ± 4.02 (7.8–25.5) lower border of mandible:
22
Canals of Lingual Foramina showed an anastomosis with the mandibular incisive canal
(35.5 %), with the mandibular canal in the area of the mental
Several studies have evaluated the canals originating from foramen (61.3 %), or with the posterior portion of the man-
the lingual foramina with respect to trajectory, length, and dibular canal (3.2 %). A detailed evaluation of the frequency,
connections within the mandibular body (Figs. 22.19, 22.20, course, and anastomosis of lingual bony canals was per-
22.21, 22.22, 22.23, and 22.24). Trikeriotis et al. (2008) formed by von Arx et al. (2011) using CBCT. MLF always
evaluated the linguobuccal communications of lingual presented bony canals with 8.1 % connecting with the man-
canals in 50 patients using CT. Such connections were dibular incisive canal. In the remaining 91.9 % of canals
observed in 14 cases (28 %), and two different types were originating from MLF, no anastomosis was visible in CBCT
described. Type I characterized the lingual canal originating images. In contrast, 62.8 % of LLF showed a radiographi-
from a lateral lingual foramen and connecting with the man- cally visible anastomosis with the mandibular incisive canal
dibular incisive canal and, as such, communicating with the (64.5 %), with the mandibular canal (28.9 %), and with an
buccal bone plate through the mental canal and mental fora- adjacent tooth apex (5 %). The majority of canals originat-
men (24 % of patients). Type II comprised the median (mid- ing from LLF showed a forward direction (76.9 %). In
line) lingual canal traversing the symphysis to the buccal 22.3 % the canal entered the lingual plate perpendicularly,
bone plate (4 % of patients). and only one canal (0.8 %) exhibited a posterior trajectory.
A detailed analysis with spiral CT of 132 midline lingual A recent CBCT study of 500 patients revealed lateral lin-
bony canals was performed by Liang et al. (2006) who gual vascular canals (LLVC) in 24.8 % of the cases (Sahman
showed that 53 % of the canals originated from a lingual et al. 2014). The majority of LLVC (83 %) were observed in
foramen above or at the level of the genial tubercles. The the premolar areas. In 98.2 %, the LLVC communicated
mean length of these canals was 4.1 mm with 77.8 % of them with the mandibular incisive canal and in only 1.8 % with
showing a downward pattern. The remaining 47 % of the the mandibular canal.
detected canals initiated from a lingual foramen below the A study evaluating 20 cadaveric mandibles with micro-
genial tubercles. The mean length of the inferior canals was CT and 3D reconstructions differentiated the course of lin-
3.8 mm with 91.9 % having an upward direction. Overall, the gual canals originating from superior and inferior midline
superior and inferior canals extended toward the buccal bone lingual foramina (Choi et al. 2013). Upper lingual canals
for an average of 37 % of the bone width. most frequently traveled downward (68 %), whereas lower
A detailed analysis of midline lingual foramina and their lingual canals showed an equal occurrence of upward (37 %)
canals with CBCT imaging in 36 patients showed that 62 % and horizontal (37 %) courses. According to Tepper et al.
of the canals had a descending course, 17.3 % had a horizon- (2001), lingual canals originating from LLF always exhibit
tal course, and 20.7 % had an upward trajectory (Babiuc an intraosseous course in the ventral direction and are located
et al. 2011). Bifurcations occurred in 12.1 % of the identified in the lingual portion of the mandible over their entire length.
canals. Regarding the penetration depth in the sagittal plane, A recent study evaluating CBCT scans taken of 120 dry
19.4 % of the canals were only located in the lingual third of mandibles found in some instances an anastomosis between
the symphysis, 52.8 % reached the middle third, and 27.8 % superior and inferior MLF canals resulting in a continuous
spread to the buccal third. No information was provided canal between the midline foramina (Oettle et al. 2015).
whether the canals communicated with the buccal bone sur- The authors postulated the lingual canals followed this cir-
face. In the axial plane, only 9.2 % of the canals were ori- cular pathway to run toward a capillary bed contained
ented anteriorly, whereas slight deviations to the right within the cancellous bone of the mandible providing nutri-
(54.5 %) or to the left (36.3 %) were more common. ents to the mandible. Such an area might explain excessive
In a CBCT study of 181 patients with 154 lingual foram- bleeding during implant drilling or harvesting of bone
ina, Katakami et al. (2009) reported 31 lingual canals that blocks from the chin.
478 22 Lingual Foramina and Canals
MLF su
MLFsu
GT
MLF in
GT
MLFin Fig. 22.21 Sagittal CBCT image showing two median lingual canals
forming what appears to be an anastomotic loop within the body of the
anterior mandible in an 85-year-old male. White spot is a metal marker
Fig. 22.19 Sagittal CBCT image showing two median foramina and of a diagnostic splint. GT genial tubercle, MLFin inferior median lin-
corresponding canals with the lower canal connecting to the buccal gual foramen, MLFsu superior median lingual foramen
bone surface (linguobuccal communication). GT genial tubercle,
MLFin inferior median lingual foramen, MLFsu superior median lin-
gual foramen
MIC
MLFin
MLFin
LLF
Fig. 22.20 Axial CBCT image at the level of the lower median fora- Fig. 22.22 The axial CBCT section (inferior view) shows that the
men exhibits the canal connecting to the buccal bone surface forming a canal originating from the inferior median lingual foramen connects to
linguobuccal communication. LLF lateral lingual foramen, MLFin infe- the buccal aspect of the mandible. MIC mandibular incisive canal,
rior median lingual foramen MLFin inferior median lingual foramen
Canals of Lingual Foramina 479
MIC MIC
MeC
MeF
LLF
MeF MeC
MC
MC
LLF
Fig. 22.23 Axial CBCT image (inferior view) of the right mandible Fig. 22.24 Axial CBCT image (inferior view) of the left mandible
showing a lateral lingual canal connecting to the mental canal at the demonstrating a lingual canal connecting to the mandibular incisive
level of the bifurcation of the mandibular incisive canal in a 42-year-old canal. LLF lateral lingual foramen, MC mandibular canal, MeC mental
female. LLF lateral lingual foramen, MC mandibular canal, MeC men- canal, MeF mental foramen, MIC mandibular incisive canal
tal canal, MeF mental foramen, MIC mandibular incisive canal
480 22 Lingual Foramina and Canals
Neurovascular Components of the Lingual anteriorly and superiorly to connect with the mandibular
Foramina and Canals incisive canal.
Loukas et al. (2008) examined 100 human cadaveric
The observation that at least one significant lingual midline heads injected with red latex. The main arterial supply to the
foramen is nearly always present has raised the interest of anterior mandible was provided by the sublingual artery,
anatomists and clinicians alike to evaluate the content of the either as a branch from the lingual (73 %) or from the sub-
lingual foramina and their bony canals entering the mandible mental artery (27 %). The authors further differentiated trib-
from the lingual aspect (Figs. 22.25, 22.26, 22.27, and 22.28). utaries from the sublingual artery as ascending branches
A dissection study of 28 cadaveric mandibles evaluated ana- reaching the alveolar ridge, middle arterial branches anasto-
tomically and histologically the structures associated with the mosing with the contralateral sublingual artery to enter the
midline lingual foramen (McDonnell et al. 1994). The left midline lingual foramen, and descending branches supplying
and right sublingual artery joined to form a single vessel that the lingual mucosa. Mucosal arterial branches exhibited a
consistently entered the lingual foramen. Cross-sectional his- mean diameter of 0.9 mm (0.4–1.1 mm), whereas perforat-
tology confirmed the vessel to be an artery. There was a ing branches had a mean diameter of 0.8 mm (0.6–1 mm).
plexus of perivascular vessels with small and sporadically The mean length of sublingual branches originating from the
positioned nerves around the artery, but veins were lacking lingual artery was 8 mm (range 4–12 mm) and for those orig-
Vandewalle et al. (2006) dissected ten intact cadaveric inating from the submental artery 7 mm (range 3–14 mm).
mandibles, and they found a branch of the lingual nerve and Anatomical dissection of 20 cadaveric mandibles by
of the lingual artery to enter the midline lingual foramen. Rosano et al. (2008) revealed a single vascular branch enter-
However, the authors assessed only foramina located superior ing the superior midline lingual foramen in 19 cases. The
to or at the genial tubercles. Liang et al. (2005) confirmed the single vessel was formed by anastomosis of the bilateral sub-
content of the superior genial tubercle canal to be of neuro- lingual arteries originating either from the lingual arteries or
vascular nature, including venous channels, utilizing MRI from the submental arteries.
and histology in ten cadaveric mandibles. On paraffin sec- Nakajima et al. (2014) performed a comprehensive study
tions, the mean external diameter of the lingual artery branch concerning the arterial vasculature in the sublingual and sub-
in the canal was 448 μm, the mean internal diameter was mandibular spaces and its relationship to the LLF of the man-
223 μm, the mean diameter of the nerve bundle was 64 μm, dible. In particular, they studied the origin of the facial and
and the mean diameter of the vein was 35 μm. In a subsequent lingual arteries, as well as the branching pattern and courses of
study, the same authors evaluated 12 cadaveric mandibles the submental and sublingual arteries. In 8.7 % of the dissected
using micro- and macro-anatomical dissection (Liang et al. heads, the facial and lingual arteries had a common trunk orig-
2007). They observed a clear neurovascular bundle in both inating from the external carotid artery. The relative contribu-
superior and inferior genial spinal foramina and canals. The tions to the sublingual artery of the facial and lingual arteries
contents of the superior canal were derived from the lingual were 49.3 % and 53.6 %, respectively. When the facial artery
artery and lingual nerve. For the inferior canal, however, the gave rise to the sublingual artery, the submental artery pene-
arterial origin was submental and/or sublingual and the inner- trated the mylohyoid muscle (31.2 %) or it entered the sublin-
vation originated from a branch of the mylohyoid nerve. gual space via the posterior border of the mylohyoid muscle
Madeira et al. (1978) dissected 26 cadaveric mandibles (18.1 %). Further, the authors dissected cadavers demonstrat-
and showed in 50 % of specimens that terminal branches of ing LLF on corresponding CT images to identify the origin of
the mylohyoid nerve entered the MLF. In 77 % of those the artery entering the foramen. In all cases, the “communica-
cases, the neural branches originated from the right mylohy- tion branch” that passed through the LLF originated from the
oid nerve, and in 85 % they entered via the inferior MLF. After submental artery. After entering the mandibular body, the
penetrating the lingual bone plate, anastomoses were “communication branch” either formed an anastomosis with
observed between the terminal branches of the mylohyoid the inferior alveolar artery or it divided into two separate arter-
nerve and the apices of the mandibular incisors or with the ies, one forward branch supplying the mandibular incisor area
ipsi- or contralateral mandibular incisive nerves. and the other branch running in a linguobuccal direction to the
Kawai et al. (2006) presented the results of CT analysis mental foramen supplying the lower lip.
and anatomical dissection of an 88-year-old male cadaveric Lustig et al. (2003) utilized ultrasound/Doppler to evalu-
mandible. The submental artery communicated with a lin- ate the blood supply to the MLF in 20 healthy subjects. The
gual descending artery arising from the inferior alveolar lingual foramen artery was identified as a single midsagittal
artery through a lingual canal and LLF located in the canine vessel that resulted from anastomosis of the left and right
and first premolar area. The lingual foramen was positioned sublingual arteries. The average diameter of the entering ves-
8.9 mm above the lower border of the mandible and 12.2 mm sel was 1.41 ± 0.34 mm and the average blood flow was
mesial to the mental foramen, while the lingual canal coursed 2.92 ± 3.19 mL/min.
Neurovascular Components of the Lingual Foramina and Canals 481
MLF
LLF
LLF
GT GT
Floor
of mouth
LLF
MLF
Clinical Relevance of the Lingual Foramina tissue hemorrhage. A recent cadaver study with CBCT scans
taken from the edentulous anterior mandible demonstrated
The presence of lingual foramina and lingual bony canals that a simulation of the placement of a single midline implant
has many clinical implications that can be summarized as (3.8 × 11 mm) contacted or perforated the lingual midline
follows: canal (Birkenfeld et al. 2015). If the arteries traveling within
the inferior midline lingual foramina are damaged during sur-
1. Additional neural and vascular supply to the mandible gery, it may be difficult to locate the hemorrhage since mus-
and teeth from sources other than the inferior alveolar cle attachment at the mental spine covers the sublingual
nerve and artery. region and may obscure the field (Choi et al. 2013). The arter-
2. Risk of severe hemorrhage following damage to the arterial ies most often involved in these incidents are branches from
branches entering the lingual bone plate through MLF or the sublingual or submental arteries. Unfortunately, the posi-
LLF or running close to the inner aspect of the mandible. tions of these arteries receive scant attention in standard anat-
3. Lingual foramina and canals may represent pathways for omy and surgery textbooks. Although their diameter is small
tumor spread into the body of the mandible. (1–2 mm), calculations show that within 30 min, about
420 mL of blood may escape into the sublingual or subman-
The additional innervation of teeth by terminal branches dibular spaces (Flanagan 2003).
from the lingual and mylohyoid nerve or even from the trans- Several case reports of significant bleeding have docu-
verse cervical nerve (cutaneous colli) from the cervical mented hematomas in the floor of the mouth (Figs. 22.29 and
plexus via lingual foramina and canals has been the source of 22.30) with airway complications typically following inser-
much speculation (Chapnick 1980). Some authors have sug- tion of dental implants (Fig. 22.31) (Table 22.5). Perforating
gested that in certain patients, supplementary lingual infiltra- the lingual cortical plate in the interforaminal region with
tion is necessary to obtain full anesthesia of the teeth and laceration of arteries in the anterior region of the floor of the
adjacent structures following mental or inferior alveolar mouth is the most commonly cited complication. Reactive
nerve blocks (Rood 1977; Madeira et al. 1978). According to vasospasm coupled with the vasopressors used intraopera-
McDonnell et al. (1994), the midline foramen is large enough tively may delay the identification of a ruptured vessel for
to be used as a route of administration by infiltration of local hours (Loukas et al. 2008). Usually, the hematoma forms in
anesthetic solution to the mandibular incisor region. A recent the sublingual space between the mylohyoid muscles and the
systematic review demonstrated that additional lingual infil- mucosa thereby pushing the tongue upward and backward. If
tration could enhance anesthetic efficacy compared with bleeding cannot be stopped at this time, exsanguination con-
buccal infiltration alone in the pulpal anesthesia of mandibu- tinues, and the hematoma pushes the tongue further toward
lar incisor teeth (Dou et al. 2013). the pharynx resulting in airway obstruction potentially caus-
With regard to tumor spread through lingual foramina and ing a life-threatening condition.
canals, there is radiological evidence of a canalicular net- Several reports documented the difficulty or inability of
work establishing communication between the inner and nasotracheal intubation requiring an emergency tracheot-
outer bone plates in the anterior mandible. This finding could omy. Once the airway is secured, hemostasis must be accom-
provide a better understanding of bone tumor invasion and plished. Various methods have been described in the
spread (Trikeriotis et al. 2008). As a general rule, the mus- literature, such as finger compression, insertion of gauzes
cles attached to the mandible form a barrier to tumor spread and/or hemostatic agents, cauterization, and arterial ligation
except in later stages. However, resistance to tumor spread (Jo et al. 2011). The previous surgical recommendation pro-
may be diminished in irradiated mandibles. Under these cir- moting the ligation of the lingual artery has been overshad-
cumstances, it is possible that the numerous accessory owed by the current approach advocating the ligation of the
foramina found on the inner aspect of the mandible could submental artery or, possibly the facial artery, based on
facilitate a direct pathway into the cancellous bone compart- newer clinical data (Bavitz et al. 1994; Weibrich et al. 2002).
ment (Fanibunda and Matthews 2000). In fact, implant placement should be performed at a facility
By far the most frequently documented complication located reasonably close to a hospital where a life-threatening
related to lingual foramina is the surgical damage to arterial hemorrhagic complication can be promptly and effectively
branches causing hemorrhage in the area within or around the addressed by personnel with specialized cardiovascular
MLF/LLF (Kalpidis and Setayesh 2004; Romanos et al. training and equipment (Boyes-Varley and Lownie 2002).
2012a), promoting the study of the blood supply in this region A closer look at the published case reports reveals two
(Chap. 24) (Hofschneider et al. 1999; Mardinger et al. 2007; interesting aspects: the site of surgical perforation and the
Fujita et al. 2012). According to McDonnell et al. (1994), the age of the patient. Perforation of the lingual cortex in the
artery entering the midline lingual foramen is sufficiently area of the canine/first premolar during implant bed prepara-
large to present difficulty in control of intraosseous or soft tion is the most frequently reported cause of hemorrhage in
Clinical Relevance of the Lingual Foramina 483
the floor of the mouth (Table 22.5). For many practitioners, and submental arteries are highly endangered in those
the interforaminal region is a supposedly safe zone for inser- patients who often also present vascular disease or bleeding
tion of endosseous dental implants (Rosano et al. 2008). disorders or are on anticoagulation therapy.
However, marked and unexpected lingual undercuts, vertical Although three-dimensional radiography can provide
bone atrophy, incorrect angulation of drills, and implant bed valuable information concerning the presence of lingual
preparations that are directed too deeply may result in perfo- foramina and bony lingual canals in the anterior mandible
ration of the lingual plate with subsequent laceration of the thus minimizing intraoperative and postoperative complica-
arterial branches entering the lingual side of the mandible. tions, it cannot provide direct insight regarding the arterial
With regard to the age, the majority of the patients of the vasculature in the floor of the mouth. As a consequence, the
reported cases were around 60 years or older (Table 22.5). clinician is advised to use extreme caution when approach-
The vascular supply to the mandible is characterized as a ing the lingual cortical plate with surgical instruments or
centrifugal pattern in young patients due to the dominance of when placing mucosal incisions lingual to the alveolar crest.
the inferior alveolar artery for distributing blood. However, a As an alternative, ultrasound/Doppler was shown to reliably
centripetal pattern gradually emerges via the buccal, facial, visualize and measure the arterial blood supply to the chin
and lingual arteries as the patient ages and succumbs to tooth region and should be sought when appropriate (Lustig et al.
loss, muscular inactivity, and arteriosclerotic alterations 2003).
(Bradley 1981). In particular, branches from the sublingual
Makris N, Stamatakis H, Syriopoulos K, Tsiklakis K, van der Stelt Rosano G, Taschieri S, Gaudy JF, Testori T, del Fabbro M. Anatomic
PF. Evaluation of the visibility and the course of the mandibular assessment of the anterior mandible and relative hemorrhage risk in
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Mardinger O, Manor Y, Mijiritsky E, Hirshberg A. Lingual periman- Sahman H, Sekerci AE, Ertas ET. Lateral lingual vascular canals of the
dibular vessels associated with life-threatening bleeding: an ana- mandible: a CBCT study of 500 cases. Surg Radiol Anat.
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Mason ME, Triplett RG, Alfonso WF. Life-threatening hemorrhage Sakka S, Krenkel C. Hemorrhage secondary to interforaminal implant
from placement of a dental implant. J Oral Maxillofac Surg. surgery: anatomical considerations and report of a case. J Oral
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Oral Med Oral Pathol Oral Radiol Endod. 2010;109:e25–31. Shiozaki K, Fukami K, Kuribayashi A, Shimoda S, Kobayashi
Nakajima K, Tagaya A, Otonari-Yamamoto M, Seki K, Araki K, Sano K. Mandibular lingual canals distribute to the dental crypts in prena-
T, Okano T, Nakamura M. Composition of the blood supply in the tal stage. Surg Radiol Anat. 2014;36:447–53.
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2001;92:597–600. Oosterbeek HS. Hemorrhage of the floor of the mouth resulting
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Tongue
23
As a simple definition, the tongue (l: lingua, g: glossa) can be ally positioned to it, the deep lingual veins and the fimbriated
characterized as a mucous membrane bag containing muscular mucosal folds. The boundary between the oral and pharyn-
tissue but without a skeleton (Figs. 23.1 and 23.2) (Takemoto geal portions of the tongue is formed by an inverted and
2001; Kajee et al. 2013). In fact, the complex intrinsic and V-shaped line called the sulcus terminalis. Several larger
extrinsic tongue muscles allow for great versatility and compli- papillae, called circumvallate, are located immediately ante-
cated movements of the tongue. The extrinsic muscles connect rior to the sulcus terminalis (Fig. 23.4). At the apex of the
the tongue to the mandible, hyoid bone, and styloid process terminal sulcus, usually a small depression called the fora-
(see below). Major functions of the tongue include articulation men cecum is visible corresponding to the embryological
(speech), movement of food during mastication, assisting swal- site of formation of the thyroid gland by epithelial invagina-
lowing, taste, and sensation (du Toit 2003a, b). The posterior tion (Sameer et al. 2012). Occasionally, persistence of a thy-
tongue performs a critical role in upper airway maintenance. It roglossal duct connecting the tongue with the thyroid gland
is not surprising that the anatomy of the anterior and posterior occurs. In the adult population, a 7 % failure rate of thyro-
portions of the tongue differs with speaking and mastication glossal duct involution is estimated (Chou et al. 2013).
requiring fine motor movements, while upper airway mainte- Sanders and Mu (2013) suggested dividing the tongue
nance entails sustained muscle tone (Zaidi et al. 2013). into three parts: the base (or root) posterior to the circumval-
The tongue is usually divided into an oral (anterior two- late papillae, the body extending from the circumvallate
thirds) and a pharyngeal (posterior third) part (Fig. 23.3). papillae to the frenulum, and the blade as the part of the
The oral part fills the oral cavity proper in the closed mouth tongue anterior to the frenulum. The body, the largest seg-
position, whereas the pharyngeal part forms the vertical tran- ment of the tongue, was further differentiated into an anterior
sition of the tongue to the epiglottis. The pharyngeal portion portion lying below the hard palate and a posterior portion
is also called the root (l: radix) of the tongue. The dorsal positioned below the soft palate.
surface of the oral part is partly keratinized and contains Four cranial nerves contribute to the innervation of the
three different types of mucosal projections or papillae: fili- tongue (Zur et al. 2004). The lingual nerve of the mandibular
form papillae (pointed), fungiform papillae (round), and foli- division of the trigeminal nerve (CN V) provides general
ate papillae (linear). The latter are located at the posterior somatic afferent fibers to the anterior two-thirds of the
sides of the tongue whereas the filiform and fungiform papil- tongue. It further conveys taste afferents that are relayed via
lae are evenly distributed on the dorsal surface. The ventral the chorda tympani to the facial nerve (CN VII) from the
and lateral surfaces of the tongue are covered with a nonke- same region. The glossopharyngeal nerve (CN IX) supplies
ratinized mucosa and also contribute to the floor of the mouth general and taste sensation to the posterior third of the
(Chap. 24). Several features characterize these surfaces, tongue. The hypoglossal nerve (CN XII) provides the motor
including the lingual frenulum along the midline, and later- supply to the muscles of the tongue (Zur et al. 2004).
uvula
CvP
GGM
anterior
mandible
GGM
Ep
GHM
GHM
Fig. 23.3 Midsagittal section through the dissected lower jaw and third, red double arrow). CvP circumvallate papillae, Ep epiglottis,
tongue of a cadaveric head. The tongue consists of an oral part (two GGM genioglossus muscle, GHM geniohyoid muscle
anterior thirds, blue double arrow) and a pharyngeal part (posterior
FC
CvP
CvP
CvP
492 23 Tongue
Size of the Tongue sus) and terminate in the tongue, whereas the intrinsic muscles
originate and terminate within the tongue mass. It is generally
Lauretano et al. (1997) assessed the size of the tongue in ten accepted that activation of the intrinsic tongue muscles alters
fresh cadaveric heads. The mean length of the tongue mea- the tongue shape, whereas activation of the extrinsic tongue
sured from the foramen cecum to the tip was 7.5 ± 1.0 cm muscles is associated with the position and movement of the
(range 6–9 cm). The mean width was 4.5 ± 0.7 cm (range tongue (Mu and Sanders 2010). No single tongue motion is the
3.5–5.5 cm), and the mean height (foramen cecum to hyoid result of one muscle. The complex myoarchitecture of inter-
bone) was 3.1 ± 0.7 cm (range 2.3–4.5 cm). digiting muscle fibers contribute to the apparent limitless num-
ber of deformations of the tongue’s shape (Zaidi et al. 2013).
The position of the tongue relative to the upper and lower
Tongue Muscles jaws is regulated in part by the position of the hyoid bone,
which, with the anterior and posterior suprahyoid muscles,
The human tongue consists of eight pairs of skeletal muscles controls the angulation and length of the floor of the mouth
(Fig. 23.5). Four pairs of extrinsic muscles including the genio- on which the tongue body “rides.” Feeding and speech can-
glossus, styloglossus, and hyoglossus, all originate from bony not be solely attributed to the tongue but rather to the jaw-
surfaces, while the palatoglossus originates from the soft pal- hyoid-tongue complex, or the hyomandibular “kinetic chain”
ate. The remaining four intrinsic muscles lack bony support (Hiiemae and Palmer 2003). Tongue behavior cannot be
(Fig. 23.6) and include the transversal, vertical, inferior longi- divorced from hyoid movement that is directly linked to
tudinal, and superior longitudinal components (Table 23.1) motion of the mandible. The length and angulation of the
(Mu and Sanders 2010; Zaidi et al. 2013). Extrinsic muscle floor of the mouth on which the tongue body rides are dic-
fibers have external bony attachments (except the palatoglos- tated by that linkage (Hiiemae and Palmer 2003).
StP
PGM
SGM
GGM
HGM
GT
HB
Fig. 23.5 Illustration of the extrinsic tongue musculature viewed from the right lateral perspective. GGM genioglossus muscle, GT genial tuber-
cle, HB hyoid bone, HGM hyoglossus muscle, PGM palatoglossus muscle, SGM styloglossus muscle, StP styloid process
Tongue Muscles 493
SLM
PGM PGM
SGM SGM
TVM TVM
ILM ILM
GGM GGM
HGM HGM
median
raphe
HB
Extrinsic Tongue Muscles and 23.13). It arises from the greater horn and the anterior
surface of the body of the hyoid bone. It ascends vertically
The genioglossus is the largest muscle in the tongue muscula- and enters the lateral aspect of the tongue between the stylo-
ture (Figs. 23.7, 23.8, 23.9, and 23.10). It is a fan-like muscle glossus located laterally and the inferior longitudinal muscle
that arises in the midline from a short tendon attached to the bundles positioned medially. The styloglossus and hyoglos-
superior genial tubercles behind the mandibular symphysis but sus muscles compose the posterior lateral surface of the
above the origin of the geniohyoid muscle. Grossly, it is shaped tongue. They converge and intermix at the level of the tongue
like a wedge with the sharp anterior edge corresponding to the base, and then together they pass anteriorly spanning the
frenulum. It was found to be composed of three fiber groups: a whole length of the tongue. From the base to tip, the
lower horizontal, an intermediate, and a superior oblique por- styloglossus-hyoglossus combination composes the ventro-
tion. The lower fibers insert into the tongue base and hyoid lateral surface of the tongue just beneath the mucosa.
bone, the intermediate fibers gradually change their course and Throughout its course, the hyoglossus lies deep to the stylo-
radiate into the tongue’s body, whereas the upper fibers run glossus except at its posterior edge where the muscles merge
upward, forward, and slightly outward to attach to the dorsum (Takemoto 2001; Mu and Sanders 2010; Boland et al. 2013).
lamina propria near the tip of the tongue. In the midline, the Occasionally a so-called chondroglossus muscle is
fibro-fatty median raphe is well defined and separates the reported although its existence is debated. It arises from the
genioglossus muscle into distinct left and right muscle bellies medial side of the lesser horn of the hyoid bone and passes
(Takemoto 2001; Mu and Sanders 2010; Boland et al. 2013). directly upward to blend with the intrinsic muscular fibers of
The styloglossus muscle arises from the anterolateral the tongue, between the hyoglossus and genioglossus mus-
aspect of the styloid process and passes downward and for- cles (Sanders and Mu 2013). Ogata et al. (2002) dissected
ward to extend into the lateral border of the tongue the chondroglossus muscle in 50 Japanese cadavers and
(Fig. 23.11). After reaching the tongue posterior to the pala- found it in all specimens. Originating mainly from the medial
toglossal arch, the styloglossus muscle divides into three side of the lesser horn of the hyoid bone, the chondroglossus
segments. The anterior fibers run to the apex, the middle muscle passed upward to penetrate the inferior longitudinal
fibers stretch medially to join fibers of the transverse muscle, muscle of the tongue. Ascending inside the genioglossus
and the posterior fibers run downward and intersect with muscle, its bundles spread and changed direction anteriorly,
fibers of the hyoglossus (Takemoto 2001; Mu and Sanders but never extend beyond the sulcus terminalis.
2010). In a recent cadaver study with dissection of 23 The palatoglossus muscle is the smallest of all extrinsic
tongues, Saito and Itoh (2007) showed that anterior muscle muscles and often difficult to identify (Fig. 23.14). This
bundles of the styloglossus run from the lateral surface to the muscle arises from the soft palate, runs downward anterior
lower surface of the tongue to join the contralateral bundles to the palatine tonsil forming the palatoglossal arch, and
anterior to the genioglossus to form a large arch of a single reaches the substance of the tongue anterior to the styloglos-
muscle layer. Throughout its course from tongue base to sus. Then, this muscle runs anteroinferiorly, but more
apex, the styloglossus remains superficial and distinct from obliquely than the styloglossus, finally merging with the lat-
the hyoglossus (Boland et al. 2013). ter (Takemoto 2001; Boland et al. 2013). The palatoglossus
The hyoglossus is a thin muscle that is quadrilateral in muscle may also be categorized as part of the soft-palate
shape when viewed from the lateral perspective (Figs. 23.12 musculature.
Extrinsic Tongue Muscles 495
GHM
SLGr
SLGl
LN
GGM GGM
GT
GHM
GHM
tip of
tongue
GGM GGM
LN
HGN HGN
LA
ECA
LA
GGM
MHM
HGM
Fig. 23.12 Right lateral view of HGN
the hyoglossus muscle in a HGM
dissected cadaveric head. The
hypoglossal nerve runs lateral to
LA
the hyoglossus muscle as it
courses superiorly to the tongue.
hyoid bone
ECA external carotid artery, FA
facial artery, HGM hyoglossus SMGl
muscle, HGN hypoglossal nerve,
LA lingual artery, MHM skin of
mylohyoid muscle, SMGl left right neck
submandibular gland, SMGr right
submandibular gland (elevated
with a hemostat)
498 23 Tongue
hard palate
soft palate
PGM
PGM
tongue
uvula
Intrinsic Tongue Muscles tongue. The muscle is composed of two bellies arranged in
parallel, i.e., a lateral and medial compartment (Mu and
The superior longitudinal muscle comprises a flat sheet that Sanders 2010).
covers the dorsal (superior) surface of the tongue (Figs. 23.15 The transverse and the vertical intrinsic muscles form the
and 23.16). It lies just beneath the surface, and it is intimately core of the tongue. Both muscles are organized into numerous
attached to the dorsal tongue mucosa. Fascicles are arranged alternating muscle fiber layers arranged perpendicular to each
longitudinally within this sheet muscle; however, these fas- other. The transverse fiber layers connect the median septum to
cicles do not course the entire length of the tongue. Instead the lateral margin of the tongue, whereas the vertical fibers are
they are composed of groups of short muscle fibers. These attached both to the dorsal and ventral mucosa of the tongue
fascicles interweave throughout the length of the superior (Mu and Sanders 2010). According to Saigusa et al. (2004) the
longitudinal muscle merging and splitting at short intervals posteroinferior portion of the transverse intrinsic muscle forms
(Mu and Sanders 2010). a ring of muscle together with the superior pharyngeal constric-
The inferior longitudinal muscle is cylindrical in shape tor, and it may largely be responsible for the retrusive move-
and situated ventrally between the hyoglossus and the genio- ment of the tongue and the constrictive movement of the
glossus muscles. It extends from the base to the tip of the pharyngeal cavity as an antagonist to the genioglossus muscle.
DLA
tip of
tongue
GGM
GGM
LA
500 23 Tongue
Lingual Nerve
angle of
ECA
mandible
OA
FA
HGN
SMG
FA
HGN
LA
HGN
HGM
HGN
LA
LN LN
HGN HGN
Hypoglossal Nerve (range 12–25 mm) superior to the common carotid bifurca-
tion (Bademci and Yasargil 2006).
The hypoglossal nerve (CN XII) carries exclusively efferent The hypoglossal nerve usually divides into a lateral
motoric fibers and controls the complex movements of the branch supplying the hyoglossus, styloglossus, and inferior
tongue innervating the intrinsic and extrinsic tongue muscles longitudinal muscles and into a medial branch innervating
(Lin and Barkhaus 2009) (Figs. 23.10, 23.12, 23.13, 23.17, the genioglossus, superior longitudinal, vertical, and trans-
23.18, 23.19, and 23.20). Its name derives from its course verse muscles (Mu and Sanders 2010). The human hypo-
below (“hypo”) the tongue (“glossus”). The hypoglossal glossal nerve is normally monofascicular, becoming
nerve innervates all extrinsic and intrinsic muscles of the polyfascicular only in its distal third where it branches (Zaidi
tongue except the palatoglossus muscle. The latter is sup- et al. 2013).
plied by the cranial portion of the accessory nerve (XI) The distribution pattern of the hypoglossal nerve was
running with the vagus nerve (CN X) via the pharyngeal studied in detail in ten postmortem tongues (Mu and Sanders
plexus. In addition to the neural control of tongue movement, 2010). After the hypoglossal nerve reached the dorsal sur-
the hypoglossal nerve also has a role in respiration and swal- face of the hyoglossus muscle, the nerve usually gave off its
lowing (Bademci and Yasargil 2006). first branch to innervate the geniohyoid muscle. It was then
The hypoglossal nerve originates from its nucleus within divided into a lateral and a medial branch to supply different
the medulla oblongata. The hypoglossal nerve exits the skull tongue muscles. After the lateral branch arose from the
base through the hypoglossal canal that is located inside the hypoglossal nerve, the remaining medial branch turned
occipital bone below the jugular foramen. It descends in medially at the anterior edge of the hyoglossus muscle and
close contact with the vagus nerve and eventually leaves the began to run anteriorly. Overall, the hypoglossal nerve gave
carotid space between the internal jugular vein and internal off approximately 50–60 primary nerve branches along its
carotid artery. It then courses anteroinferiorly toward the whole course within the tongue.
hyoid bone lying below the posterior belly of the digastric In general, the hypoglossal nerve branched in the follow-
muscle. Within the posterior sublingual space, the hypoglos- ing order from the root to the apex of the tongue (Mu and
sal nerve lies between the hyoglossus (medial) and mylohy- Sanders 2010): geniohyoid (not a tongue muscle), superior
oid muscles (lateral) and gives off its branches to the muscles longitudinal, styloglossus, hyoglossus, lateral inferior longi-
of the tongue (Loh et al. 2002; Alves 2010). In addition, it tudinal (intrinsic), horizontal portion of genioglossus,
contributes to the ansa cervicalis that innervates the infrahy- oblique portion of genioglossus, posterior transverse and
oid muscles (Jelev 2013). The course of the hypoglossal vertical (intrinsic), medial inferior longitudinal (intrinsic),
nerve is remarkably consistent albeit variants have been and anterior transverse and vertical (intrinsic). The trans-
described by Islam et al. (2012). MRI is considered the pre- verse muscle group that comprised the core of the tongue
ferred imaging modality to visualize the hypoglossal nerve appeared to have the most complex innervation with the
(Alves 2010). highest percentage of motor end plates. The innervation of
The extracranial course of the hypoglossal nerve has been the human tongue showed specializations not reported in
divided into a descending, horizontal, and ascending portion other mammalian tongues, including nonhuman primates.
(Kim et al. 2003). The descending portion refers to the hypo- These specializations appear to allow for fine motor control
glossal nerve before it loops around the occipital artery, the of tongue shape.
horizontal portion refers to the hypoglossal nerve crossing
the hyoglossus muscle, and the ascending portion denotes
the distal part of the hypoglossal nerve reaching the intrinsic Glossopharyngeal Nerve
tongue muscles.
In a dissection study of 10 cadaveric heads (20 sides), the The glossopharyngeal nerve (CN IX) is a mixed nerve of
hypoglossal nerve was found to be located on average parasympathetic, motor, taste, somatosensory, and viscero-
4.5 mm (range 3–7 mm) below and mostly superficial to the sensory fibers (Ong and Chong 2010). It supplies the stylo-
tendon of the posterior belly of the digastric muscle (Bademci pharyngeus muscle, the mucous membranes of the pharynx,
and Yasargil 2006). The hypoglossal nerve usually loops and the posterior third of the tongue (Ozveren et al. 2003).
around the occipital artery (a branch from the external carotid The glossopharyngeal nerve carries general visceral efferent
artery) as it changes its trajectory from vertical to horizontal fibers to the parotid gland (Larson et al. 2002). The glosso-
directions. In all cadavers, the hypoglossal nerve crossed the pharyngeal nerve originates from the nucleus ambiguous
occipital artery 7–9 mm (mean 8 mm) superior to the emer- within the medulla oblongata. It leaves the cranial fossa via
gence of the occipital artery from the external carotid artery, the jugular foramen posteromedial to the styloid process and
and the hypoglossal loop was located on average 19 mm the styloid muscles. The glossopharyngeal nerve then travels
504 23 Tongue
downward along the stylopharyngeus muscle and perforates divisions. Occasionally, the facial and lingual arteries pres-
the pharynx wall at the level of the middle constrictor muscle ent a common trunk (Troupis et al. 2011). Very rarely, a com-
(Prades et al. 2014). mon thyrolingual trunk has been described (Lemaire et al.
In a study evaluating three fresh adult human tongues 2001). The lingual artery courses anteriorly between the
(Sihler’s staining and microdissection), branches of the glos- hyoglossus positioned laterally and the genioglossus mus-
sopharyngeal nerve were observed that extended anteriorly cles. It generally branches into the deep (dorsal) lingual
beyond the sulcus terminalis, with projections also along the artery that enters the body of the tongue and into the sublin-
lateral lingual margin anterior to the foliate papillae (Doty gual artery that continues to the anterior floor of the mouth
et al. 2009). The authors speculated that these glossopharyn- (Chap. 24) (Dallan et al. 2013).
geal projections might sustain taste function in the anterior In a dissection study of 20 adult cadaveric heads, the lin-
two-thirds of the tongue after surgical damage to the chorda gual artery branched from the external carotid artery at a
tympani. Further, in the same study, anastomotic branches mean distance of 19.6 ± 8.7 mm superior to the carotid bifur-
between the glossopharyngeal and lingual nerves were cation (Ozgur et al. 2008). The mean diameter of the lingual
detected within the tongue body raising the possibility of artery at its origin was 3.1 ± 0.65 mm. In 90 % of the cases,
functional interactions between CN V and CN IX (Doty the lingual artery originated as a separate vessel. A common
et al. 2009). The glossopharyngeal nerve entered the tongue linguofacial trunk was present in 7.5 % and a thyrolingual
at the most posterolateral portion. The main trunk bifurcated trunk in 2.5 %.
into medial and lateral primary branches (Fig. 23.20). The Fazan et al. (2009) evaluated the origin and course of the
medial branch subdivided into about five rami that inner- lingual artery in 81 sides of embalmed cadaveric heads. In
vated separate circumvallate papillae, whereas the lateral 77.8 % of the cases, the lingual artery had the typical origin,
branch ran in an anterolateral direction. Some terminal rami but in 22.2 % a common linguofacial trunk was observed.
of the lateral glossopharyngeal branch were coursing clearly However, the latter finding was only present bilaterally in
into the middle third of the tongue (Doty et al. 2009). two cadavers. The mean distance between the lingual artery
and the common carotid artery bifurcation was 10.5 ± 1.1 mm
(right side) and 10.2 ± 1.1 mm (left side), respectively, and
Vagus Nerve did not differ statistically from mean distances observed in
cases with a common linguofacial trunk: 11.6 ± 1.5 mm
A small area of the tongue just anterior to the epiglottis is (right side) and 10.5 ± 0.9 mm (left side). The diameter of the
innervated by the vagus nerve (CN X). The vagus nerve is lingual artery at its origin was 2.5 ± 0.1 mm (right side) and
mixed conveying complex modalities through parasympa- 2.6 ± 0.1 mm (left side), respectively. The diameter of the lin-
thetic, motor, taste, and sensory fibers. It provides the major guofacial trunk at its origin was 2.1 ± 0.2 mm (right side) and
parasympathetic (efferent secretomotor) and afferent vis- 2.4 ± 0.2 mm (left side), respectively. No significant differ-
cerosensory supply to the head and neck, as well as the tho- ences were observed comparing sides or type of origin of the
racic and abdominal viscera (Ong and Chong 2010). The lingual artery.
vagus nerve exits the skull base via the jugular foramen. It In a dissection study of ten cadaveric heads (20 sides), the
descends along the entire carotid space lodged in the poste- mean length of the lingual artery was 9.7 ± 0.83 mm (Guan
rior groove between the internal jugular vein and the internal et al. 2005). In another dissection study of 54 formalin-fixed
carotid artery, then common carotid arteries, and enveloped cadaveric heads, the lingual artery was located in 84.6 % of
by carotid fascia. The vagus nerve is intimately connected the specimens below the hypoglossal nerve at an average dis-
with the cranial component of the accessory nerve (IX), and tance of 3.2 ± 1.3 mm and above the hyoid bone at a mean
these combined fibers are transmitted via the pharyngeal distance of 6.3 ± 3.9 mm (Homze et al. 1997).
plexus to serve as the principal motor supply for the soft pal-
ate and pharyngeal constrictor muscles (Ong and Chong
2010). Lingual Veins
sublingual vein and follows the hypoglossal nerve to termi- every imaginable form is unique to humans and a large part
nate either in the lingual vein or directly into the internal of speech articulation (Stone et al. 2001).
jugular vein. Interconnections between the lingual and hypoglossal
nerves within the tongue body are clinically significant in the
linguohypoglossal reflex as an important mediator of tongue
Lymphatics movement via the lingual nerve (Zur et al. 2004). They may
also serve a role in surgical sensory reinnervation of the
The tongue displays a dense subcutaneous lymphatic plexus tongue (Zur et al. 2004).
that increases in density from the tip to the base and three The external component of the hypoglossal nerve is fre-
primary routes can be identified for oral part (Werner et al. quently identified during neck dissection, carotid endarterec-
2003). Although the drainage pattern is characterized as a tomy, and other procedures involving the deep spaces of the
central versus lateral tributary system, crossover occurs at neck. Although palsy or paralysis to a unilateral hypoglossal
the midline enabling bilateral movement of infection. The tip nerve will disturb speech, hinder swallowing, and plague the
of the tongue drains inferiorly into the submental nodes that patient with tongue biting, bilateral loss of CN XII nerve
are positioned in the submental triangle. These, in turn, drain function can be crippling with possible loss of upper airway
either into the submandibular group or directly into the control and potentiating the inability to swallow and speak
jugulo-omohyoid group of the deep cervical chain of nodes. (Kim et al. 2003). The clinical evaluation of the hypoglossal
The lateral aspect of the tongue drains via the submandibular nerve includes inspection of the tongue’s morphology (atro-
nodes that are scattered over the submandibular gland and phy, fasciculation) and of the tongue’s movements (difficulty
within the submandibular space. The medial portion of the in protrusion, deviation, etc.) as well as of articulation and
oral part of the tongue drains centrally and directly into the speech (Loh et al. 2002).
deep cervical lymph nodes. The pharyngeal portion of the The tongue plays a key role in the development of obstruc-
tongue also drains centrally into the deep cervical lymph tive sleep apnea (OSA) that affects over 6 % of adults (Lowe
node group but typically via the retropharyngeal lymph node 1980; Zaidi et al. 2013). Progressive loss of lingual and pha-
chain in the retropharyngeal space. ryngeal tone in the upper narrow airway is the primary cause
The lateral lingual lymph nodes have been described in of OSA. Muscle fibers in the posterior tongue are predomi-
conjunction with the submandibular lymph node group nantly fatigue resistant that are responsible for the long sus-
(Ananian et al. 2015). In a study of 21 cadaveric dissections, tained tonic activities required for maintaining the tongue’s
these authors reported an incidence of 33.3 % with a mean position and preventing its mass from falling into the retro-
nodal length of 4.1 mm (range of 1.4–8.7 mm) and thickness glossal airway. The human tongue is a muscular hydrostat
of 2.8 mm (range of 0.8–7.5 mm). The authors advocated and hence would benefit from a sophisticated hypoglossal
that the lateral lingual lymph nodes should be removed dur- nerve stimulation system that is capable of achieving a con-
ing a glossectomy. certed spatiotemporal interplay of multiple tongue muscles,
Nodular lymphatics are particularly pronounced along including retrusors (Zaidi et al. 2013).
the posterior surface of the pharyngeal part of the tongue
aggregating to form lingual tonsils. These tonsils, along
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Floor of Mouth
24
The floor of the mouth is a horizontally aligned U-shaped mandible to the body of the tongue (Fig. 24.3). Other impor-
space situated in the part of the oral cavity that is located tant structures of the floor of the mouth include the subman-
beneath the tongue (La’porte et al. 2011) (Figs. 24.1 and dibular duct, the large veins, the sublingual and submental
24.2). As such, the floor of the mouth represents the inferior arteries, and their branches. According to Agarwal and
(caudal) anatomical boundary of the oral cavity. The main Kanekar (2012), CT is the imaging modality of choice for
structures of the floor of the mouth include the mylohyoid evaluating inflammatory processes, mandibular cortical bone
muscles, the geniohyoid muscles, the sublingual glands, the erosion, cutaneous changes, and submandibular duct calculi,
deep processes (oral parts) of the submandibular glands, and whereas MRI is particularly useful for staging of oral malig-
the lingual mucosa stretching from the inner aspect of the nancies involving the floor of the mouth.
SFD
SFD
*
SLC SLC
*
*
*
Fig. 24.1 Anterosuperior view
of the floor of the mouth in a
61-year-old male. Note the
multiple bilateral exostoses (tori
mandibulares, *) in the premolar
regions and the lingual frenulum
(arrow). SFD sublingual fold,
SLC sublingual caruncle
SLC
SLC
DgMab DgMab
platysma
Mylohyoid Muscle 509
Mylohyoid Muscle size of the mylohyoid hiatus and hernia in 23 adult cadavers
(Harrison et al. 2013). A hiatus was found in 43 % of the
The mylohyoid muscle is a broad and flat muscle connecting cadavers, and a hernia protruded through every hiatus. Such
the mandible and the hyoid (Figs. 24.4, 24.5, 24.6, and 24.7). hiatus appeared either as a fusiform fissure in line with the
It is an anterior suprahyoid muscle and is located superior to transverse fibers of the mylohyoid muscle or as an oval open-
the anterior belly of the digastric muscle (Otonari-Yamamoto ing. The median anteroposterior size was 7 mm (range
et al. 2010). The mylohyoid muscle forms a quadrilateral 2–11 mm), and the median mediolateral dimension was
sheet, and its fasciae converge medially to insert in the mylo- 14 mm (range 7–20 mm). The horizontal distance from the
hyoid raphe, a sagittal fibrous lamina that runs from the sym- symphysis to the anterior margin of the hiatus varied from
physis to the hyoid bone (Gervasio et al. 2011). The 10.5 to 36 mm. The length of the mylohyoid muscle ranged
mylohyoid muscle is often referred to as the muscular dia- from 36 to 50 mm, and the majority of hernias were observed
phragm of the mouth separating the oral cavity from the in the anterior two-thirds of the muscle. Histologically, sub-
hyolaryngeal complex. The mylohyoid muscle divides the lingual gland tissue was identified in 60 % of the hernias,
lower part of the oral cavity into a sublingual space posi- while the other 40 % presented as fat tissue.
tioned superior to the muscle and a submandibular space The mylohyoid muscle is innervated by the mylohyoid
located inferior to the muscle but superior to the hyoid bone nerve that is a branch of the mandibular division (CN V3)
(Agarwal and Kanekar 2012). The mylohyoid muscle sling from the trigeminal nerve (Chap. 19). A rare variant with the
thus separates the floor of the mouth laterally from the right hypoglossal nerve giving rise to bilateral branches innervat-
and left submandibular spaces and anteriorly from the mid- ing the mylohyoid muscle has been reported (Madhyastha
line submental space (La’porte et al. 2011). The mylohyoid et al. 2009). The functions of the mylohyoid muscles depend
muscle is also considered a key landmark for imaging of the on the surrounding structures. When the hyoid bone is fixed,
oral cavity and upper neck (Otonari-Yamamoto et al. 2010). the mylohyoid depresses the mandible and contributes to the
The mylohyoid muscle originates from the mylohyoid opening of the mouth. In contrast, when the mandible is
line, a bony ridge on the inner aspect of the mandible fixed, the mylohyoid elevates and pulls forward the hyoid
(Fig. 24.8). Since the mylohyoid line is oblique relative to bone and thus participates in swallowing.
the occlusal plane and to the inferior border of the mandible, The mylohyoid muscle is often perforated by a large ves-
the origin of the mylohyoid muscle is also oblique relative to sel originating from the submental artery (see below).
the structures mentioned above. The fibers run downward Lymphatic vessels have been documented to pass from the
and medial to join the midline and to insert to the lower ante- tongue or from the floor of the mouth through the mylohyoid
rior portion on the body of the hyoid bone (Sonoda and muscle to drain into the submandibular nodes (infrequent
Tamatsu 2008). The anterior part of the mylohyoid muscle finding) or jugular chain of lymph nodes (frequent finding)
may be separated from the posterior portion by a fissure or (Abe et al. 2003).
defect of variable width sometimes referred to as a bouton- Windisch et al. (2004) evaluated the frequency, size,
niere (commonly identified as an anatomic variant). An and content of gaps in the mylohyoid muscle of 205 human
extension of the sublingual gland may pass through this cadaveric hemiheads. In 12.2 % of the specimens, gaps
opening and enter the submandibular space (Gervasio et al. were found, usually in the anterior two-thirds of the mylo-
2011; La’porte et al. 2011; Harrison et al. 2013). The occa- hyoid muscle; however, bilateral occurrence was seen in
sional or permanent penetration of the sublingual gland only 28 % of those cases with gaps. The mediolateral
through the mylohyoid muscle is not a rare finding, and this dimension of the gap ranged between 8 and 32 mm, and
herniation can be found in almost every fifth individual using the anteroposterior dimension ranged between 3 and
ultrasound. This may present clinically as a permanent swell- 24 mm. In 72 % of cases with gaps, the sublingual gland
ing and may be of value in the differential diagnosis of swell- bulged over the inferior border of the mylohyoid muscle.
ings in the submandibular region (Kiesler et al. 2007). A In the remaining 28 %, the muscular hiatus was filled with
recent postmortem study assessed the frequency, shape, and fat tissue.
510 24 Floor of Mouth
MHM SHM
DgMab
DgMpb
MHM SCM
Fig. 24.6 Intraoral view of the right mylohyoid muscle. The mandible
has been separated at the midline with the right mandibular body later-
ally reflected. LN lingual nerve, MHM mylohyoid muscle, SLG sublin-
gual gland, SMG submandibular gland, SMGup uncinate process of LN
submandibular gland
LN
tongue
SMGup
MHM
SLG
MHM
SMG
right left
DgMab DgMab
MHM
hyoid bone
512 24 Floor of Mouth
M3
MHR
SLF
SMF SMF
Geniohyoid Muscle Geniohyoid atrophy was found in older subjects and was
associated with aspiration status (Feng et al. 2013). The
The geniohyoid muscles are located between the genioglossus geniohyoid muscles are innervated by a branch from the
positioned superiorly, and the mylohyoid muscles located infe- ventral ramus of cervical nerve C1 that travels along the
riorly (Figs. 24.9, 24.10, and 24.11). The geniohyoid muscles hypoglossal nerve to the floor of the mouth. Based on mea-
are distinguished as two cord-shaped muscles running in an surements to determine physiological cross-sectional areas
anteroposterior direction from the symphysis to the hyoid bone. of swallowing muscles taken from 13 hemisected head and
They originate from the lower genial tubercles and attach to the neck formalin-fixed cadaveric specimens, the geniohyoid
superior part of the anterior surface of the body of the hyoid muscle was determined to possess the greatest potential
bone (Sonoda and Tamatsu 2008). Their functions are similar to among the suprahyoid muscles to displace the hyoid in the
those of the mylohyoid muscles. The geniohyoid muscle is an anterior direction while the mylohyoid muscle was most
important component of swallowing by elevating and stabiliz- likely to move the hyoid in the superior direction (Pearson
ing the hyoid bone, thus protecting the airway (Feng et al. 2013). et al. 2011).
Geniohyoid Muscle 513
PB PB
SLG SLG
SLC SLC
right
SMG
MHM
514 24 Floor of Mouth
left FA
GHM
right
GHM LA HGN
HGM
SMG
Fig. 24.14 After incision of the oral mucosa, the mucous-filled inclu-
Fig. 24.13 Massive swelling (“ranula”) of the left sublingual gland sion is clearly visible
(retention phenomenon) in a 58-year-old female
516 24 Floor of Mouth
Submandibular Gland its course medial to the sublingual gland and eventually ter-
minates at the sublingual caruncles (see above) (Beahm
The submandibular glands are characterized by two parts et al. 2009).
with respect to the mylohyoid muscle, a larger inferior por- The region of the submandibular gland is often referred to
tion and a smaller superior portion also referred to as the as the submandibular triangle that is bounded anteriorly and
lingual extension (Figs. 24.5, 24.6, 24.9, 24.12, 24.15, 24.16, posteriorly by the two bellies of the digastric muscle and
and 24.17). The inferior portion also runs superficially and superiorly by the mylohyoid muscle. In this area, the lingual
lies directly beneath the superficial layer of the deep cervical bone plate of the mandible frequently shows a depression,
fascia below the mylohyoid muscle and posterior to the facial the so-called submandibular fossa (Chap. 14), with the sub-
artery (Gervasio et al. 2011). Anteriorly, the almond-shaped mandibular gland lying against the bone concavity.
inferior portion runs parallel to the anterior belly of the Neural supply of the submandibular gland is identical to
digastric muscle in the axial plane (Ching and Ahuja 2002). that described above for the sublingual gland. The facial
Posteriorly, the inferior portion of the submandibular gland artery is the major source of arterial supply to the subman-
folds around the free posterior edge of the mylohyoid muscle dibular gland (Nadershah and Salama 2012). Arteries within
as a fingerlike projection and forms the uncinate process. the gland show a tree-like branching pattern of three levels
This superior portion of the gland resides above the muscle with main branches, secondary branches, and terminal
within the posterior aspect of the floor of the mouth and branches. The structures of the blood vessels and ducts are
extends anteriorly between the mylohyoid muscle laterally similar at each level in the lobules (Xu et al. 2011). Lymphatic
and hyoglossus muscle medially contacting the posterior drainage of the submandibular glands occurs via subman-
aspect of the sublingual gland (Gervasio et al. 2011). dibular nodes and then to the deep cervical nodes.
The submandibular duct (Wharton’s duct) begins by Zhang et al. (2010) evaluated 60 submandibular ducts in
numerous branches that exit the deep surface of the gland. It 30 adult human cadaveric heads using microscopic dissec-
is named after Thomas Wharton (1614–1673) who was an tion. The mean length of the duct was 62.0 ± 2.3 mm, and the
English physician and anatomist that researched and pre- mean diameter was 3.0 ± 1.2 mm. Horsburgh and Massoud
cisely described the submandibular glands and ducts (2013) studied the submandibular ducts of 24 patients (mean
(Horsburgh and Massoud 2013). The duct bends sharply at age 51 ± 16.5 years, range 18–85 years) using digital sub-
the posterior margin of the mylohyoid to form the genu of traction sialography. The mean length of the duct was 58 ±
the duct (Horsburgh and Massoud 2013). The duct then runs 8.8 mm (range 42–76 mm). Mean proximal, middle, and dis-
anteriorly between the mylohyoid and genioglossus muscles tal width of the duct measured 2.0 ± 0.9 mm, 2.7 ± 0.9 mm,
alongside the tongue. The duct traverses the lingual nerve and 2.1 ± 0.8 mm, respectively. The angle of the genu was on
approximately in the region of the second molar. It continues average 115 ± 16.2° (range 80–144°).
FA
mandibular border
angle of
mandible
FA
ECA SMA
right
SMG
left
SMG
right
SMG
Fig. 24.17 Superoanterior view of the left oral cavity floor follow-
ing separation of the mandible at the midline and reflection of the
left mandibular body laterally showing the submandibular duct and
associated structures. IAN inferior alveolar nerve, LN lingual nerve,
MHM mylohyoid muscle, SLG sublingual gland, SMD submandibu- IAN
lar duct, SMGup uncinate process of the submandibular gland
left aspect
of tongue
SMGup
LN
MHM
SMD
SLG
MHM
anterior
mandible
518 24 Floor of Mouth
Blood Vessels of the Floor of the Mouth a sublingual artery was found in the floor of the mouth with
a mean diameter of 2.04 mm (range 1.5–2.5 mm). The perfo-
The major arterial supply to the floor of the mouth is pro- rating branch of the submental artery was found in 41.2 %
vided by the sublingual and submental arteries (Figs. 24.18, and had a mean diameter of 2.11 mm (range 1–3 mm). The
24.19, 24.20, and 24.21). The sublingual artery originates point of perforation within the mylohyoid muscle was
from the lingual artery. The lingual artery typically arises as located on average 30.6 mm (range 2.4–47 mm) posterior to
the fourth branch of the external carotid artery but may form menton. Based on their findings, the authors reported three
a common trunk with the facial artery (Chap. 23). The lin- patterns of predominant arterial supply to the floor of the
gual artery travels anteriorly along the medial aspect of the mouth:
central region of the hyoglossus muscle (Fujita et al. 2012).
The lingual artery divides at the anterior border of the hyo- • Class I (58.8 %) with a sublingual artery, but absence of
glossus muscle into the deep lingual artery that enters the the perforating branch from the submental artery
body of the tongue and the sublingual artery. The sublingual • Class II (29.4 %) with the perforating branch, but no sub-
artery then passes medial to the sublingual gland and pro- lingual artery
vides branches to the gland, to the floor of the mouth and the • Class III (11.8 %) both sublingual artery and perforating
lingual gingiva (Bavitz et al. 1994). branch of submental artery present, with some cases dem-
The submental artery is the largest branch of the facial onstrating anastomoses between the two arteries
artery before the latter ascends over the inferolateral border
of the mandible. The submental artery originates at the level Atamaz Pinar et al. (2005) dissected 50 submental arter-
of the superior edge of the submandibular gland (Atamaz ies in 25 adult human cadavers. After bifurcation, the mean
Pinar et al. 2005). It then courses anteromedially below the diameter of the submental artery was 1.88 ± 0.48 mm (range
mylohyoid muscle along the lower aspect of the mandibular 1.02–2.72 mm) on the right side and 1.80 ± 0.46 mm (range
border. Often, an arterial branch originating from the sub- 0.82–2.80 mm) on the left side. In 60 % of the dissections, a
mental artery ascends and perforates the mylohyoid muscle large branch originated from the proximal part of the sub-
(Kim et al. 2012). This branch provides additional blood mental artery near the posterior belly of the digastric muscle.
supply to the anterior part of the floor of the mouth and the This branch then perforated the mylohyoid muscle and
anterior lingual gingiva. Terminal branches from both the coursed deep to the anterior sublingual space and anasto-
sublingual and submental arteries have been categorized as mosed with sublingual vessels. The mean diameter of the
ascending, middle, and descending branches (Loukas et al. perforating branch was 1.48 ± 0.65 mm (range 0.42–
2008; Fujita et al. 2012). The ascending branches travel to 2.42 mm) on the right side and 1.25 ± 0.58 mm (range 0.50–
the alveolar ridge, the middle branches often anastomose 2.32 mm) on the left side. In 20 % of the specimens, the
with the contralateral branches, and the descending branches authors observed a terminal branch of the submental artery
travel to the lower anterior part of the floor of the mouth. Any running to the skin of the chin and anastomosing with the
of these branches may enter the lingual plate of the anterior labiomental or inferior labial arteries to contribute to the
mandible through lingual foramina and canals (Chap. 22). A arterial supply of the lower lip.
communicating arterial branch through the mylohyoid mus- Mardinger et al. (2007) determined the size and distances
cle from the submental artery to a lingual arterial branch of unspecified blood vessels (veins or arteries) in cross sec-
from the inferior alveolar artery via a lingual foramen in the tions of twelve human cadavers at three locations. In the
premolar region has also been reported (Kawai et al. 2006). canine, mental foramen, and second molar regions, the mean
Several studies have documented the course, dimension, distances between the blood vessel and the lingual plate were
and topography of the sublingual and submental arteries. 2.8 mm (range 1–7.5 mm), 3.95 mm (range 1–9 mm), and
Bavitz et al. (1994) assessed the arteries of the floor of the 2.8 mm (range 1–7 mm), respectively. The mean diameter of
mouth in a dissection study of 74 adult human cadavers. In the dissected vessels was 1.5 mm (range 0.5–3 mm). In the
47.4 % of specimens, a normal sublingual artery was present. canine area, 11 out of 12 vessels were found above the mylo-
However, in the remaining 52.6 %, the sublingual artery was hyoid muscle. In contrast, seven out of nine vessels in the
missing or insignificant. In those cases, a large perforating second molar region were located below the mylohyoid
branch of the submental artery was found. Overall, 59.7 % of muscle.
dissections revealed an arterial branch of the submental Loukas et al. (2008) evaluated the anatomical variation in
artery that perforated the mylohyoid muscle. The site of per- arterial supply of the anterior mandible in 100 human cadav-
foration was on average 37 ± 8.6 mm (range 20–55 mm) pos- eric heads. In 73 %, the sublingual artery originated from the
terior to menton. lingual artery to give ascending (72 %), middle (98 %), and
Hofschneider et al. (1999) similarly evaluated 17 cadav- descending (54 %) branches. In the other 27 %, the sublin-
eric heads with 34 bilateral dissections. In 70 % of the cases, gual artery originated from the submental artery (note that
Blood Vessels of the Floor of the Mouth 519
the authors did not specify whether that branch perforated or the mouth. The site of perforation was located on average
circumvented the mylohyoid muscle), giving off ascending 25.1 ± 10.6 mm posterior to the chin with the majority
(69 %), middle (98 %), and descending (50 %) branches. (73.3 %) of perforations within the anterior third of the
Mucosal branches of the sublingual artery had a mean diam- mylohyoid muscle. The mean diameter of the perforating
eter of 0.9 mm (range 0.4–1.1 mm) and were found in 72 % branch was 2.03 ± 0.69 mm. Ascending branches penetrat-
in the lateral incisor area, in 62 % in the canine area, and in ing deep into the masticatory mucosa were seen in the ante-
81 % in the first premolar area. The bone-perforating rior tooth region in 44 %, in the premolar region in 18 %,
branches had a mean diameter of 0.8 mm (range 0.6–1.0 mm) and in both regions in 37 %. No ascending branches were
and were observed in 98 % to enter the midline lingual observed in the molar region.
foramina and in 53 % through lateral lingual foramina. Katsumi et al. (2013) evaluated the variations of the arte-
Kim et al. (2012) specifically assessed the topography of rial supply to the floor of the mouth in 27 formalin-fixed adult
the submental artery in 26 embalmed adult hemifaces. The human cadaveric heads. They categorized the arterial supply
mean vertical distance between the artery and the inferior into four types (Fig. 24.22). Type I (63 %) showed a large
border of the mandible ranged between 5.9 and 7.8 mm and branch of the sublingual artery supplying the sublingual
generally decreased toward the premolar. The mean horizon- space. The submental artery coursed below the mylohyoid
tal distance between the submental artery and the lingual muscle and mainly distributed to the chin. Only fine branches
bone plate ranged between 1.8 and 2.8 mm and increased pierced the mylohyoid muscle to anastomose with branches
gradually as the artery coursed anteriorly. The mean diame- of the lingual artery. In type II (5.6 %), both the sublingual
ter of the submental artery decreased from 1.6 mm in the and submental arteries supplied the sublingual space with a
third molar area to 0.8 mm in the first premolar area. In 54 % large branch of the submental artery perforating the mylohy-
of the specimens, main branches of the submental artery per- oid muscle. In type III (29.6 %), no sublingual artery was
forated the mylohyoid muscle at various sites but most fre- present. The sublingual space was supplied by the submental
quently in the first molar region. artery that divided into two branches with one running anteri-
Fujita et al. (2012) evaluated in detail the sublingual and orly below the mylohyoid muscle and the other coursing
submental arteries in 90 dissections of 45 formalin-fixed above or perforating the mylohyoid muscle. In type IV
cadaveric heads and in ten dissections of five fresh cadav- (1.8 %), the superior branch of the submental artery distrib-
eric heads. In 55 %, a sublingual artery was present, and in uted also to the tongue (absence of deep lingual artery). In the
9 % an anastomosis was observed between the sublingual majority of the specimens, the arteries supplying the sublin-
and submental arteries. In all 45 % specimens lacking a sub- gual space ran medial to the sublingual gland (74.1 %),
lingual artery, the submental artery perforated the mylohy- whereas in the remaining cases, the arteries were located
oid muscle and distributed to the anterior part of the floor of between the gland and the lingual plate of the mandible.
520 24 Floor of Mouth
Clinical Relevance of the Floor of the Mouth when performing incisions of the mucosa of the floor of the
mouth, the course and location of the sublingual gland and
As described in Chap. 22, the arteries of the floor of the mouth the submandibular duct must be taken into consideration to
running close to the lingual plate or even entering the lingual avoid damage to these delicate tissues.
aspect of the mandible are at risk during surgical procedures Since the sublingual space has no posterior border, hema-
in the mandible. Incisions on the medial and linguo-anterior tomas and infections may spread posteriorly into the sub-
aspect of the mandible must be carefully planned and per- mandibular and parapharyngeal spaces or inferiorly via the
formed to avoid damage to the arteries in the floor of the gap within the mylohyoid muscle to the submandibular and
mouth. Similarly, osteotomies and bone preparations must be submental spaces. A plunging ranula, i.e., an inferiorly
carefully executed to avoid lingual penetration through the directed penetration of the sublingual gland through the ana-
mandibular cortex and rupture of blood vessels in the vicinity tomical variant of a fissure or opening in the mylohyoid
of the lingual cortex. According to the findings of a large muscle, must be considered as a differential diagnosis of
branch of the submental artery ascending and perforating the swellings in the submandibular area. The floor of the mouth
mylohyoid muscle, it has been suggested to change the proto- may be affected by different pathologic processes including
col of extraoral ligation of the lingual/sublingual arteries and cystic lesions, vascular lesions, neoplasms, and inflamma-
first ligate the submental/facial arteries for hemorrhage con- tory conditions of various causes, e.g., dental infections and
trol of the floor of the mouth (Bavitz et al. 1994). Further, obstruction of salivary ducts (Agarwal and Kanekar 2012).
DLA
FA
HGM
Fig. 24.18 Illustration of the blood supply to the SLA
floor of the mouth viewed from right side LA
following removal of the right half of the
mandible. DLA deep lingual artery, ECA external PB
MHM
carotid artery, FA facial artery, HB hyoid bone,
HGM hyoglossus muscle, LA lingual artery, SMA
MHM mylohyoid muscle, PB perforating branch ECA HB
of submental artery, SLA sublingual artery, SMA
submental artery
Clinical Relevance of the Floor of the Mouth 521
SMG SLA
SMA
MHN
MHM
a b
IAN IAN
FA FA
LN LN
HGN HGN
ECA HGM SMA ECA HGM SMA
HB HB
Fig. 24.22 Variations in the arterial supply to the floor of the mouth based on Katsumi et al. 2013; medial view of the left side of the floor of the
oral cavity; (a) type I, (b) type II, (c) type III, (d) type IV; for details see text. DLA deep lingual artery, ECA external carotid artery, FA facial artery,
HB hyoid bone, HGM hyoglossus muscle, HGN hypoglossal nerve, IAN inferior alveolar nerve, LA lingual artery, LN lingual nerve, MHM mylo-
hyoid muscle, MHN mylohyoid nerve, PB perforating branch of submental artery, SGG submandibular ganglion, SLA sublingual artery, SLG
sublingual gland, SMA submental artery, SMD submandibular duct, SMGup uncinate process of submandibular gland
Clinical Relevance of the Floor of the Mouth 523
c d
IAN IAN
FA FA
LN LN
LA PB LA MHM PB
MHM
HGN
HGN
HGM SMA
ECA HGM SMA ECA
HB HB
The temporomandibular joint (TMJ) is a synovial joint and located at the caudal portion of the temporal bone immedi-
the only true joint in the oromaxillofacial region. It is also ately anterior to the external acoustic opening (Figs. 25.5 and
referred to as mandibular joint or craniomandibular articula- 25.6). The glenoid fossa is bordered anteriorly by a bony
tion. The TMJ is unique with regard to its rotary (ginglymoid) protuberance, the articular tubercle. The head of the TMJ is
and translatory (arthrodial) movements during jaw function the caput mandibulae of the condylar process that is the pos-
including mouth opening and closure, mastication, and terior projection of the mandibular ramus and positioned
speech. The right and left joints cannot move independently opposite from the anterior projection or coronoid process.
since they are joined via the mandible forming a bicondylar The TMJ is divided into an upper and a lower compart-
articulation (Alomar et al. 2007). Furthermore, the teeth ment by an articular disk. The latter plays an important role
serve to guide and limit certain mandibular movements. As in TMJ function and allows complex jaw movements. The
the name implies, two bones contribute to the TMJ, i.e., the TMJ is surrounded by a capsule and by several ligaments.
temporal bone and the mandible (Figs. 25.1, 25.2, 25.3, and Mandibular motions can be continuous or intermittent
25.4). and result in static and/or dynamic loading of the
The socket or glenoid fossa of the TMJ is formed by the TMJ. Basically, three types of loading can be distinguished:
mandibular fossa, a mediolaterally elongated concavity compression, tension, and shear (Kuroda et al. 2009).
sphenoid
temporal bone bone
zygomatic bone
CM
CP
3
2
ramus
temporalis
muscle
CM
CP
Fig. 25.2 Right lateral view of a
cadaveric head dissection
demonstrating the region of the ramus
temporomandibular joint (black
dotted circle). CM condyle of
mandible, CP coronoid process,
TBz zygomatic process of
temporal bone
25 Temporomandibular Joint 527
TBz
AT
EAC
CM
CP
MP
TBz
StP
ramus FOv AE AT
FSp
GF
Fig. 25.5 Inferior view of dry skull showing the glenoid (mandibular)
fossa. AE articular eminence, AT articular tubercle, EAC external audi-
tory canal, FOv foramen ovale, FSm foramen stylomastoideum, FSp
foramen spinosum, GF glenoid fossa (mandibular fossa), TBz zygo-
matic process of temporal bone
TBz
AT
AT GF
EAC
CM
EAC
CP PPF
StP
MP
MF
Fig. 25.6 Left lateral view of a dry skull demonstrating the region of
Fig. 25.4 Sagittal CBCT image of the temporomandibular joint in a the glenoid (mandibular) fossa, AT articular tubercle, EAC external
22-year-old female. AT articular tubercle, CM condyle of mandible, CP auditory canal, GF glenoid fossa (mandibular fossa), MP mastoid pro-
coronoid process, EAC external auditory canal, MF mandibular cess, PPF pterygopalatine fossa, StP styloid process, TBz zygomatic
foramen process of temporal bone
528 25 Temporomandibular Joint
head of condyle
head of
condyle
PF
neck of condyle
MF
La
Fig. 25.9 Detailed right superior view of the condylar process in a dry
Fig. 25.7 Detailed right lateral view of the condylar process in a dry skull. La lingula, MF mandibular foramen, PF pterygoid fovea
mandible
GF
head of condyle
CP
EAC
AT
CM
PF
neck of condyle
MF
La
Fig. 25.8 Detailed right anteromedial view of the condylar process in Fig. 25.10 Sagittal CBCT image of the right temporomandibular joint
a dry mandible. CP coronoid process, La lingula, MF mandibular fora- of a 33-year-old male. Note the thin bone separating the glenoid fossa
men, PF pterygoid fovea from the middle cranial fossa. AT articular tubercle, CM condyle of
mandible, EAC external auditory canal, GF glenoid fossa (mandibular
fossa)
530 25 Temporomandibular Joint
TBz CP
middle cranial fossa
GF
CM
AT
CM
EAC
Fig. 25.11 Coronal CBCT image with anterior and medial views of
the left temporomandibular joint of a 22-year-old female. CM condyle
of mandible, GF glenoid fossa (mandibular fossa)
Fig. 25.12 Axial CBCT image demonstrating spatial relationships
among right temporomandibular joint structures in a coronal plane of a
22-year-old female. AT articular tubercle, CM condyle of mandible, CP
coronoid process, EAC external auditory canal, TBz zygomatic process
of temporal bone
TB
AT
AD STA
LPMsh
Clinical Relevance Detamore MS, Athanasiou KA. Structure and function of the temporo-
mandibular joint disc: implications for tissue engineering. J Oral
of the Temporomandibular Joint Maxillofac Surg. 2003;61:494–506.
Fujita S, Iizuka T, Dauber W. Variation of heads of lateral pterygoid
Each TMJ is a pressure-bearing compound double synovial muscle and morphology of articular disc of human temporoman-
joint which is uniquely characterized by having movements dibular joint – anatomical and histological analysis. J Oral Rehabil.
2001;28:560–71.
not only controlled by the morphology of the joints them-
Haiter-Neto F, Hollender L, Barclay P, Maravilla KR. Disk position and
selves but also by the dentition at the other end of the lever the bilaminar zone of the temporomandibular joint in asymptomatic
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muscular components is constantly challenged throughout Med Oral Pathol Oral Radiol Endod. 2002;94:372–8.
Kuroda S, Tanimoto K, Izawa T, Fujihara S, Koolstra JH, Tanaka
life to adapt to occlusal changes such as eruption and loss of
E. Biomechanical and biochemical characteristics of the mandibular
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Miloglu O, Yilmaz AB, Yildirim E, Akgul HM. Pneumatization of the
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Nakai M, Abe M, Miyazaki A, Fujimiya M, Hiratsuka H. Macroscopic
muscular disturbances in the oromaxillofacial and cranial
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Pedulla E, Meli GA, Garufi A, Cascone P, Manadala ML, Deodato L,
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Masticatory Muscles
26
The masticatory muscles can be considered the engines of mandibular nerve extending as the third division of the tri-
mandibular jaw movements. The main masticatory muscles geminal nerve (CN V). The highly complex pattern of man-
include the masseter, temporalis, medial, and lateral ptery- dibular jaw movements depend on which muscles are active
goid muscles (Table 26.1) (Figs. 26.1 and 26.2). They all and whether they contract uni- or bilaterally.
originate from the cranium (fixed part) and extend to various The suprahyoid musculature may also contribute to man-
parts of the mandible (mobile part). Tendon attachments of dibular jaw movements, provided the hyoid bone is fixed in a
the masticatory muscles show periosteal, osseous, or carti- stable position relative to the mandible (Chap. 24). However,
laginous insertions (Hems and Tillmann 2000). The mastica- the suprahyoid muscles are only considered as an adjunct to
tory muscles are all innervated by branches from the the main masticatory muscles.
TM
LPMsh
LPMih
MPM
MM
Fig. 26.1 Illustration of right masseter and temporalis muscles. MM Fig. 26.2 Illustration of right medial and lateral pterygoid muscles.
masseter muscle, TM temporalis muscle LPMih inferior head of lateral pterygoid muscle, LPMsh superior head
of lateral pterygoid muscle, MPM medial pterygoid muscle
Masseter Muscle 537
the masseter that interdigitate in a saw-like fashion during contraction. In females, the corresponding values
referred to as tendinous digitations. The number of tendi- were 11.6 ± 1.4 mm and 11.9 ± 1.6 mm. Older individuals
nous digitations was typically two in males and three in and males presented significantly thicker masseter muscles
females while the length of the tendinous digitations was (p < 0.01). Kant et al. (2014) also used ultrasonography to
approximately three-quarters of that of the muscle (Lee assess the cross-sectional thickness of the masseter in 20
et al. 2012). healthy individuals with a mean age of 22.3 ± 2.0 years. The
Kiliaridis et al. (2003) determined the thickness of the mean thickness in relaxation was 10.5 ± 2.1 mm on the right
masseter in 60 young and healthy individuals between ages and 10.3 ± 1.7 mm on the left. During contraction, the mean
7–18 years using ultrasonography. In males, the mean thickness increased to 14.2 ± 2.7 mm on the right and to
thickness was 12.1 ± 2.2 mm in relaxation and 12.4 ± 2.2 14.7 ± 1.7 mm on the left.
BFP
1
PG
MeN
3 2 1
PG FV
RMV
MM
FA
EJV
FV
IJV
PD
MM
PG
540 26 Masticatory Muscles
Temporalis Muscle Akita et al. (2001), the main part of the fan-shaped tempora-
lis is sandwiched in its anterior portion by the so-called
The temporalis originates from the temporal lines of the pari- anteromedial and anterolateral muscle bundles of the tempo-
etal bone of the skull, and its fibers converge and descend ralis. The main part originates from a wide field on the lateral
into a tendon that passes through the gap formed between the surface of the skull, converges downward, passes deep to the
zygomatic arch and the side of the skull (Benninger and Lee zygomatic arch, and inserts at the coronoid process. In con-
2012) (Figs. 26.10, 26.11, 26.12, 26.13, 26.14, and 26.15). trast, the anteromedial muscle bundle originates from the
The temporalis inserts into the coronoid process and onto the infratemporal crest of the greater wing of the sphenoid bone
anterosuperior margin of the ramus. In fact, the attachment and inserts anteromedially into the coronoid process and the
of the temporalis tendon along the anterior aspect of the temporal crest of the ramus. The anteromedial muscle bundle
ramus may bifurcate and reach down to the medial and lat- of the temporalis is located on the lateral surface of the apo-
eral borders of the retromolar triangle (Benninger and Lee neurosis of the main part of the temporalis (Akita et al.
2012). The authors also speculated that the extended area of 2001).
tendon attachment along the anterior border of the ramus The temporalis muscle can be palpated above the zygo-
better counterbalances the forces generated by the large tem- matic arch, and its powerful contraction can be felt in the
poralis muscle. same location. Deep temporal nerves originating from the
Due to its fan-shaped pattern, anterior muscular fibers of mandibular nerve provide motoric innervation. Once the
the temporalis run vertically, middle fibers course obliquely, mandibular nerve exits the foramen ovale, the anterior
and posterior fibers display a nearly horizontal direction. division immediately gives off the masseteric and deep tem-
Due to the arrangement of the fibers in various directions, the poral branches that innervate the masseter and temporalis
temporalis elevates and retracts the mandible. According to muscles, respectively. These two branches run laterally along
542 26 Masticatory Muscles
the roof of the infratemporal fossa and emerge from the fascia and enters the muscle on its lateral surface (Cheung
upper border of the superior head of the lateral pterygoid 1996).
muscle before exiting the infratemporal fossa. The deep tem- A variant muscle considered as an intermediary remnant
poral nerves reach the infratemporal crest and turn superi- connecting the temporalis and the lateral pterygoid was
orly, traveling along the surface of the squamous portion of described by Akita et al. (2001). These authors found an
the temporal bone and the greater wing of the sphenoid bone, aberrant muscle that originated from the medial surface of
eventually entering and innervating the deep surface of the the anteromedial bundle of the temporalis and inserted into
temporalis muscle (Quek et al. 2014). the inferolateral surface of the lower head of the lateral pter-
Chang et al. (2013) studied the functional compartmental- ygoid in 4.5 % of 66 dissected half-heads.
ization of the temporalis muscle in ten cadavers. Five func- Gaudy et al. (2001) studied the temporalis in 169 fresh
tional compartments and innervations were identified and cadavers using anatomical dissection and MRI. Once the
summarized as follows: anterosuperior innervated by the temporal fascia had been removed, the muscle appeared to
anterior deep temporal nerve, midsuperior by the middle be made up of two parts characterized by a clear difference
deep temporal nerve, posterosuperior by the posterior deep in color. The darker anterior or orbital portion was not con-
temporal nerve, anteroinferior by the buccal nerve, and pos- nected to the lighter temporal part located posteriorly. The
teroinferior by the masseteric nerve. orbital part mainly consisted of fleshy fibers that ended in a
The arterial supply to the temporalis muscle is from three strong tendon inserting on the anteromedial aspect of the
primary arteries. The anterior and posterior deep temporal temporal ridge of the coronoid process. The temporal part of
arteries arise from the maxillary artery within the infratem- the temporalis muscle demonstrated a large, transparent, and
poral fossa. Both arteries enter the muscle on its medial fan-shaped tendon close to the surface. The tendon ended on
aspect below the zygomatic arch (Veyssiere et al. 2013). The the coronoid process with its insertion mainly on the medial
third artery is the middle temporal that is a branch from the aspect of the process and also extending down to the retro-
superficial temporal artery. This vessel supplies the temporal molar triangle.
Temporalis Muscle 543
TM
TM
STA
ZB
CM
CP
ramus
544 26 Masticatory Muscles
temporal fascia
STA
zygomatic arch
ZB
TM CM
CP
Temporalis Muscle 545
1
2
GGM
LN anterior
mandible
HGN
MHM
masseter
muscle
1
2
1
548 26 Masticatory Muscles
tongue
DLA
IAN
MHN
midial
pterygoid
muscle
midial
pterygoid
SML LN
muscle
Lateral Pterygoid Muscle 549
joint capsule. However, the firm connection between the cap- considered the lateral pterygoid as a single functional unit
sule and the disk strongly suggested that the muscle would because of its penniform structure. Further, discal and condy-
influence the movements of the disk. lar fibers were not separated. The authors also commented
Bravetti et al. (2004) histologically assessed the relation that the anterior separation of the lateral pterygoid into two
of the lateral pterygoid with the neck of the mandible and the entities is due to variations in the course of the maxillary
disk in six TMJ specimens. The insertion of the muscle artery. When the latter was superficial, the lateral pterygoid
extended over a height of 1 cm as far down to the mandibular was more homogenous and the separation into two heads
incisure and also comprised the whole width of the condylar only existed at the level of the pterygoid origins.
neck. The surface insertion widely overlapped the limits of Apart from a motor branch formed by the lateral pterygoid
the pterygoid fossa anterolaterally. The attachment of the lat- nerve from the anterior root of the mandibular nerve, several
eral pterygoid to the anterior part of the disk, but limited to other nerves contribute to the innervation of the lateral ptery-
the medial part, was only about 2 % of the whole muscular goid including the anterior, middle, and posterior deep tempo-
insertion. Hence, the bulk of muscular fibers of the lateral ral nerves, the masseteric nerve, and even the buccal nerve
pterygoid was found to pass under the foot of the disk to (Davies et al. 2012). According to these authors, neuromuscu-
attach to the condylar head. lar partitioning of the lateral pterygoid may allow for selective
El Haddioui et al. (2005) studied the lateral pterygoid activation of the different parts of the lateral pterygoid to
in 179 fresh cadavers using anatomical dissection and MRI. ensure coordination of movements and stress reduction for the
The muscle was found be made up of eight alternating TMJ. Vascular supply to the lateral pterygoid muscle occurs
musculoaponeurotic layers arranged horizontally. The authors through an arterial branch from the maxillary artery.
temporal bone
STA
ZB
LPMsh
CM
Fig. 26.21 Left lateral view of a LPMih
dissected cadaveric head with the
coronoid process of the mandible LBN
and the zygomatic arch removed
showing the two parts of the
lateral pterygoid muscle. CM
condyle of mandible, LBN long
buccal nerve, LPMih inferior ramus
head of lateral pterygoid muscle,
LPMsh superior head of lateral LBN
pterygoid muscle, STA superficial
temporal artery, ZB zygomatic
bone
Lateral Pterygoid Muscle 551
LBN
ramus
552 26 Masticatory Muscles
LBN
LBN
Imaging of the Masticatory Muscles the CSA of the masseter (4.6 cm2) and medial pterygoid
(2.5 cm2) showed a significant decrease (11.3 % and 14.3 %,
Hsu et al. (2001) studied the size of the masseter and medial respectively), while the CSA of the lateral pterygoid
pterygoid muscles in 27 young males having a complete (4.7 cm2) significantly increased by 22.7 %.
dentition, class I occlusion, and normal muscle and jaw Ng et al. (2009) quantitatively assessed the volumes of the
function. MRI images were obtained from the zygomatic masticatory muscles in 12 healthy subjects of 20–25 years of
arch to the hyoid bone. The mean volume of the masseter age utilizing MRI. The mean right and left side volumes for
was 31 cm3, whereas that of the medial pterygoid was the masseter muscles were 29.7 ± 6.8 cm3 and 29.5 ± 5.2 cm3,
11 cm3. The mean cross-sectional areas of the muscles were respectively, for the medial pterygoid 8.9 ± 1.5 cm3 and
6.2 cm2 for the masseter and 3.5 cm2 for the medial 8.7 ± 1.7 cm3, respectively, and for the lateral pterygoid
pterygoid. 10.2 ± 1.8 cm3 and 9.5 ± 2.2 cm3, respectively. The computed
Goto et al. (2005) determined the cross-sectional area volumes of the masticatory muscles showed a strong correla-
(CSA) of masticatory muscles in ten healthy individuals tion between right and left sides.
20–30 years of age using MRI. The maximum CSA at the According to Serra et al. (2008), ultrasonography is the
jaw-closed position of the masseter was the largest (5.2 cm2). preferred imaging technique of masticatory muscles because
The lateral pterygoid (3.8 cm2) and the medial pterygoid of its safety and cost advantages, and it is as reliable and
(3.0 cm2) showed clearly smaller CSA. After jaw opening, precise as CT and MRI.
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Index
Lesser palatine foramina (LPF), 208, 212 illustration of the classification, 348, 349
Lesser palatine nerve (LPN), 218 incidence and types, 346–347
Levator labii superioris (LLS), 3, 5, 7, 8 bone surfaces, distances from, 337–339
Levator labii superioris alaeque nasi (LLSAN), 3, 5, 7, 8 clinical relevance of, 365
Lingual concavity, 295, 298 components of, 340–342
Lingual foramina, 463 course of, 330–333
aspect of, 464 and dental implants, 360–361
canals of, 477–479 radiographic identification, 324–329
clinical relevance of, 482–483 size of, 334
coronal CBCT image, 465, 467 and third molars, 350–351
frequency and location, 468–471 axial CBCT image, 352, 356, 357
hematoma, case reports of, 484–485 coronal CBCT section, 352, 353, 356, 357
lingual view, 463 location of, 359
median and corresponding canals, 464 molar, roots of, 351
neurovascular components and canals, 480, 481 panoramic radiograph, 351, 354, 357
occlusal view, 463 patient declined complete extraction, 355
radiographic detection, 472 radiographic signs, illustration of, 358
sagittal CBCT image, 463, 464 sagittal CBCT image, 353, 354, 357
size and distances of, 572–576 surgically removing, 354
3D rendering, 464, 465 Mandibular cortical grafts, 439
Lingual nerve, 239, 413, 500–502 Mandibular foramen (MF), 305, 306
anatomical distances, 414 accessory mandibular foramen, 318
chorda tympani, 417 anatomy and surrounding structures, 307, 308
clinical relevance, 422–423 antilingula, 320
communications of, 416–417 clinical relevance of, 321
diameter of, 415 lingula, 318–319
injury neurovascular structures, spatial relationship of, 317
nonsurgical, 421–422 relative position within ramus, 314
risk factors of, 418 size and distances, 309–313
risk of, 418 vertical distance from, 315–316
patterns of, 416 Mandibular incisive canal (MIC), 445, 446, 454–455
position of, 417–418 adjacent structures, distances from, 452–453
Lingual perforation, 295 axial CBCT image, 453
Lingual veins, 504–505 buccolingual CBCT section, 453
Lingula, 285, 307, 318–319 mean values, 452
Lips reformatted coronal-sagittal view, 453
anatomical landmarks, 3, 4 clinical relevance, 457–459
clinical relevance, 13 course of, 454–455
depressor anguli oris, 5, 9, 10 detection of, 448
depressor labii inferioris, 5, 9, 10 length and diameter, 449–451
external carotid artery, 6, 11 presence of, 447–449
facial artery/inferior labial artery, 7, 11 Mandibular motions, 525
horizontal labiomental artery (HLA), 7 Mandibular nerve
levator anguli oris, 3, 7 anterior trunk, 236
LLS, 3, 5, 7, 8 foramen ovale, 233–235
LLSAN, 3, 7, 8 otic ganglion, 239
mentalis muscles, 5, 9, 10 posterior trunk, 237, 238
orbicularis oris muscle, 3, 6 auriculotemporal nerve, 238
perioral facial muscles, 3–5 lingual nerve, 239
risorius and the buccinator, 6, 10 trigeminal nerve, 233, 234
smile line, 12–13 Marginal mandibular branch (MMB), 36
superior labial artery, 7 facial nerve, 33, 34
zygomaticus major and minor, 3, 7, 8 Masseter muscles, 536–538
LLS. See Levator labii superioris (LLS) CBCT images, 3D rendering, 541
LLSAN. See Levator labii superioris alaeque dissected and plastinated cadaveric head, lateral view, 540
nasi (LLSAN) origins and insertions, 538
LPM. See Lateral pterygoid muscles (LPM) plastinated cadaveric head, lateral view, 539
Lymphatics, 505 Masticatory muscles, 535
clinical relevance, 553
imaging of, 552
M lateral pterygoid muscle, 536, 549–550
Mandibular block anesthesia, 321 masseter muscles, 536–538
Mandibular canal, 323, 324 CBCT images, 3D rendering, 541
adjacent root apices, distances from, dissected and plastinated cadaveric head, lateral view, 540
335–336 origins and insertions, 538
BMC, 342–345 plastinated cadaveric head, lateral view, 539
558 Index