J Periodontol October 2008

Review
Practical Application of Anatomy for the Dental
Implant Surgeon
Gary Greenstein,* John Cavallaro,* and Dennis Tarnow*

A proficient knowledge of oral anatomy is needed to provide

effective implant dentistry. This article addresses basic anatomic structures relevant to the dental implantologist. Pertinent
muscles, blood supply, foramen, and nerve innervations that
may be encountered during implant procedures are reviewed.
Caution must be exercised when performing surgery in certain
regions of the mouth. Furthermore, numerous suggestions are
provided regarding the practical application of anatomy to
facilitate successful implant therapy. J Periodontol 2008;79:
1833-1846.
KEY WORDS
Anatomy; dental implants.

* Department of Periodontology and Implant Dentistry, New York University College of

Dentistry, New York, NY.
Private practice, Freehold, NJ.
Private practice, Brooklyn, NY.
Private practice, New York, NY.

he study of anatomy familiarizes

the implant surgeon with normal
and atypical oral structures.
Knowledge of oral structures and ordinary anatomic variations, which usually
differ with respect to size and shape,
enhance patient evaluations and facilitate precise surgical procedures. A thorough understanding of anatomy provides
the implant surgeon with the confidence
to resect or augment tissues in an attempt
to restore form, function, esthetics, and
health. This article reviews the practical
application of basic anatomy to implant
therapy. It does not attempt to discuss
every blood vessel, nerve, and muscle
found within the oral cavity, but rather it
focuses on structures routinely encountered, which are critically important to
planning and executing dental implant
surgery.

MANDIBULAR STRUCTURES
Mandibular Foramen
The location of the mandibular foramen
may vary based on race and ethnicity,
and this can affect the success of block injections.1,2 Among adult cadaveric mandibles, the foramen was found inferior to
the occlusal plane, at its level, or above
it 75%, 22.5%, and 2.5% of the time, respectively.1 In another study,2 the figures
were 29.4%, 47.1%, and 23.5%, respectively. Therefore, according to these investigations, 2.5% to 23.5% of block
injections given at the level of occlusion
would be ineffective. Accordingly, it is
doi: 10.1902/jop.2008.080086

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Application of Anatomy

advisable to inject patients 6 to 10 mm superior to the

occlusal plane,3 which usually accounts for anatomic
variations. The distance to the mandibular foramen assessed on cadavers revealed that it is within the reach
of a short needle (needle length = 21 mm).4 Therefore,
short needles can be used to attain anesthesia in the
mandible. If there are symptoms of a good block injection, but the patient is still symptomatic, infiltrate the
lingual aspect of the molar teeth, because there may
be additional innervation from C2 and C3 (cutaneous
coli nerve of the cervical plexus).5
Inferior Alveolar Canal
The trigeminal nerve, the fifth cranial nerve, has three
main branches: ophthalmic, maxillary, and mandibular.6 The mandibular nerve gives rise to the inferior alveolar nerve (IAN). It enters the mandibular canal on
the medial surface of the ramus by the lingula. The canal is ;3.4 mm wide, and the nerve is ;2.2 mm thick.7
Within the canal there is a nerve, an artery, a vein, and
lymphatic vessels. The artery lies parallel to the nerve
as it traverses anteriorly, but its position varies with respect to being superior or inferior to the nerve within
the mandibular canal.7 Therefore, it is possible to inadvertently penetrate into the mandibular canal and
induce neurologic damage without provoking hemorrhaging and vice versa.
When developing an osteotomy over the mandibular canal, cortical bone is penetrated first, and the preparation terminates within softer cancellous bone. The
mandibular canal usually has cortical bone around it,
which may provide some resistance to drilling. However, clinicians should not rely on tactile feedback to
signal the canal is about to be penetrated, because a
twist drill can enter the canal with little warning. Conversely, when traversing from more to less mineralized
regions of the posterior mandible during osteotomy
development, a sudden decrease in resistance may
give an erroneous impression that the canal has been
breached. Accordingly, there is no substitute for precise radiometrics, safety devices (e.g., drill stops),
and a plan for attaining specific implant lengths in this
region of the mouth.
The IAN may present in different anatomic configurations. The nerve may lower gently as it proceeds anteriorly, or there can be a sharp decline or the nerve can
drape downward in catenary fashion (curled as hanging between two points).8 The IAN crosses from the lingual to the buccal side of the mandible and often, by the
first molar, it is located midway between the buccal and
lingual cortical plates of bone.9 Usually, the IAN divides into the mental and incisive nerves in the premolar molar region.10 The mental nerve emerges from the
mental canal, and anterior to the mental foramen the
mandibular canal is referred to as the incisive canal.11
Implant placement buccal or lingual to the IAN is a
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risky maneuver and should not be attempted without

the aid of computed tomography (CT).
The mandibular canal bifurcates in the inferior
superior or mediallateral plane in ;1% of patients.12
A bifurcated canal may manifest more than one mental
foramen and, the bifurcation may not be seen on panoramic or periapical films. The undetected presence of
a bifurcated mandibular canal can result in an incorrect estimation of available bone superior to the mandibular canal.
Denio et al.13 evaluated cadavers to determine how
close the IAN was to the apices of mandibular posterior
teeth. The mean distance to the second molar, first molar, and premolars was 3.7, 6.9, and 4.7 mm, respectively. Similarly, Littner et al.14 reported the upper
border of the mandibular canal was located 3.5 to
5.4 mm below the root apices of first and second molars. Other investigators15 found that the canal was often close to the inferior border of the mandible. It is also
possible for the mandibular canal to be adjacent to the
apex of the mandibular molar (Fig. 1). Therefore, with
regard to developing osteotomies over the inferior alveolar nerve, it should be recognized that mean distances between apices of teeth and the nerve canal
reported in articles may not apply to any particular patient. Hence, to avoid untoward sequelae in the posterior mandible, the location of the nerve needs to be
verified before an osteotomy is created.
With regard to radiographs, Denio et al.13 reported
that in 28% of patients the mandibular canal could not
be clearly identified in the second premolar and first
molar regions on periapical radiographs. Therefore,
if the inferior alveolar canal cannot be seen on a periapical film, it is recommended to obtain a panoramic
film and adjust distances for radiographic distortion.
If it still cannot be detected, a CT scan is needed.
Osteotomies should not be developed in the posterior

Figure 1.
The mandibular canal is adjacent to the apex of the mandibular
first molar. Arrow points to mandibular canal abutting alveolus of
extracted tooth #30.

Greenstein, Cavallaro, Tarnow

J Periodontol October 2008

mandible until the position of the inferior alveolar canal

is established.
Several additional facts about radiographs should
be considered. The angulation of the periapical film
can affect the perceived location of the canal with respect to the bone crest.16 For instance, if the x-ray
beam is perpendicular to the canal, but not the film,
elongation occurs, and the canal appears further from
the crest than it really is. Conversely, when the x-ray
beam is perpendicular to the film, but is not parallel
to the canal, foreshortening happens. Table 1 lists
mean linear radiographic errors with respect to different x-ray techniques when locating the mandibular canal.17 The numbers in the table represent mean errors
and can be incorrect by even larger amounts. These inaccuracies need to be taken into account when creating
an osteotomy in sensitive areas. To avoid misinterpretation of linear measurements on radiographs, clinicians can use markers of known dimension when
taking an x-ray (e.g., 5-mm-diameter ball bearing).16
Mental Foramen and Nerve
Commonly, three nerve branches of the mental nerve
emerge from the mental foramen (each ;1 mm in diameter).11 They supply innervation to the skin of the
mental foraminal area, the lower lip, chin, mucous
membranes, and the gingiva until the second premolar. Occasionally, the mental nerve emerges from the
buccal plate of bone and reenters the alveolar bone to
provide innervation for the incisor teeth.18
The location of the mental foramen differs in the horizontal and vertical planes, and these variations may
be related to race.19-21 For example, horizontally the
foramen is often found flanked by the apices of premolars in white individuals19 and next to the apex of the
second mandibular premolar among Chinese subjects.20 Atypically, the foramen may be situated by
the canine or the first molar.20,21 In these situations,
the incisive canalstarts where the mentalnerve emerges
from the mandible.
The position of the foramen also varies in the vertical
plane.19 Pertinently, it was reported that in the first premolar area of 936 patients, the foramen was situated
coronal to the apex in 38.6% of cases, at the apex in
15.4% of cases, and apical to the apex in 46.0% of
cases. The foramens location, in relation to the second
premolar, was coronal to the apex in 24.5% of cases, at
the apex in 13.9% of cases, and apical to the apex in
61.6% of cases. Thus, caution must be exercised, especially when placing immediate implants in the premolar area, because in 25% to 38% of cases the foramen is
located coronal to the bicuspids apex.19
The anterior loop of the mental foramen refers to the
IAN when it courses inferiorly and anteriorly to the foramen and then loops back to emerge from the foramen22 (Fig. 2). Detecting and quantifying the size of

Table 1.

Distortion on Radiographs17
Type of Radiograph

Mean (mm; range)

Periapical

1.9 (0 to 5)

14

Panoramic

3.0 (0.5 to 7.5)

23

CT scan

0.2 (0.0 to 0.5)

1.8

Figure 2.
Anterior loop of the mental foramen (arrow). The inferior alveolar nerve
courses beneath and mesial to the foramen and then loops back to
emerge from the foramen.

the anterior loop was done by using diverse diagnostic

methods: panoramic films of patients, panoramic films
of markers in dried skulls and cadaver mandibles, periapical films of cadaver jaws, CT scans of patients, and
surgical cadaver dissections.23 Conflicting results with
regard to the size and prevalence of the anterior loop
may be due to different criteria used to characterize
the anterior loop and dissimilar diagnostic techniques.
Surgical dissection furnished the best evidence for
validating the presence of the anterior loop of the mental foramen.23 Furthermore, comparing radiographic
and dissection data from the same individuals supplied
insight as to the dependability of radiographs to detect
the anterior loop.24-26 In this regard, Mardinger et al.24
reported that anatomically identified loops often did
not show on periapical films, and radiographs supplied
a 40% false-positive finding when related to their corresponding cadaver dissections. In another study,25
loop dimensions varied from 0.0 to 7.5 mm on periapical radiographs and from 0 to 1.0 mm between
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Application of Anatomy

cadaver specimens; usually radiographs overestimated the extent of the anterior loop.25 In a different
investigation,26 the anterior loop was identified on 27%
(six/22) of the panoramic films and 35% (eight/22)
of the cadavers. The dimensions of anterior loops in
panoramic radiographs varied from 0.5 to 3 mm,
and cadaver specimens manifested anterior loops that
ranged from 0.11 to 3.31 mm. However, the investigators noted that 50% of the x-rays were interpreted incorrectly, and the presence of a loop was not verified
by surgical dissection. Furthermore, 62% of the surgically detected loops were not found radiographically.
In general, it can be concluded that many false-positive and false-negative findings occur when identifying
the anterior loop with x-rays.
Thus, when there is concern with respect to the location of the mental nerve, it should be exposed to
identify its position before implant insertion. First, determine on the radiograph where the mental foramen is
located. If it is in the premolar region, create a vertical
releasing incision on the mesial aspect of the canine
and reflect the flap past the mucogingival junction.
Then use wet gauze to elevate the flap apically and
expose the roof of the mental foramen.23 The gauze
shields the nerve from being damaged, and the periosteal elevator can be used to push the gauze apically. To
determine how much bone is available for implant insertion, measure the distance between the alveolar
crest and the coronal aspect of the foramen with a periodontal probe (Fig. 3). The chosen implant length
should provide a safety margin of 2 mm from the
nerve.23,27 This measurement minus 2 mm can also
be used to safely insert an implant mesial, above, or
distal to the mental foramen up to the mesial half of
the first molar area.27
When measurements are taken from the crest of the
bone to the roof of the foramen to determine the appropriate implant length in the foraminal area, there is
some additional safety room based upon three anatomic considerations: the foramen coincides with the
buccal plate and the osteotomy will be developed lingual to the foramen and its contents; the foramen is
cone shaped, with the widest part of the funnel on
the buccal aspect; and the nerve emerges from a path
inferior to the foramen.27 The mental nerve comes out
of the mental canal, which is angled upward at ;50
(range, 11 to 70) from the mandibular canal (Fig.
4).28 Therefore, it should be noted that the inferior alveolar nerve is lateral and apical to the mental foramen.
If it is desired to place an implant, which is larger
than the safety distance determined above, anterior
to the mental foramen, a CT scan is necessary to determine whether an anterior loop is present, or it is necessary to probe within the foramen to ascertain if there is
an anterior loop. In this regard, a curved probe (e.g.,
Nabers 2N probe) can be gently placed into the fora1836

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Figure 3.
To determine how much bone is available for implant insertion over the
mental foramen, measure the distance from the alveolar crest to the
coronal aspect of the foramen (arrow) with a periodontal probe.

Figure 4.
CT scan. The mental nerve emerges from the mental canal. The mental
canal is angled upward at ;50 (range, 11 to 70).

men to assess if its distal aspect is open. If it is not open,

then the nerve entered on the mesial side, and this denotes that an anterior loop is present (Fig. 5). The mesial side of the foramen is consistently patent, because
at this site the anterior loop emerges from the bone or
the incisal nerve proceeds anteriorly. Note that the patency on the mesial aspect of the foramen leading to
the incisal region and an anterior loop feel similar, and
it is not possible to distinguish between these two structures.27 It must be emphasized that probing into the
mental foramen should be done very gently; otherwise, neurologic damage can be done to the nerve.
Furthermore, even if the presence of an anterior loop

Greenstein, Cavallaro, Tarnow

J Periodontol October 2008

Figure 5.
A) If placement of the probe into the mental foramen on the distal side reveals that the mental
canal is patent, then the anterior loop is not present. B) If placement of a probe into the mental
foramen on the distal side reveals that the mental canal is not patent, then an anterior loop of
the mental nerve exists. The nerve must have traversed inferiorly and looped back to the foramen
creating an anterior loop. (Figure slightly modified from reference 23.)

is corroborated by probing, its length is still unknown.

Therefore, as a general guideline, if there is an anterior
loop of the mental foramen and a CT scan is not available to determine its dimensions, and it is desired to
place an implant deeper than the safety measurement
on the mesial aspect of the foramen, it is prudent to
place the distal aspect of the implant 6 mm anterior
to the mental foramen to avoid damaging the loop
when drilling the osteotomy.28
Mandibular Incisive Canal
Numerous investigations29-32 reported that there is a
true incisive canal mesial to the mental foramen,
which is a continuation of the mandibular canal. It has
also been noted that the incisive canal may appear
as a maze of intertrabecular spaces, which include
neurovascular bundles.33 The incisive nerve supplies
innervation to teeth (first bicuspid, canine, and lateral
and central incisors).
The incisive canal is typically found in the middle
third of the mandible (in 86% of cases).30 It usually narrows as it approaches the midline and only reaches the
midline 18% of the time.30 The nerve usually terminates
apical to the lateral incisor and sometimes apical to the
central incisor.30 The incisive canals width is 1.8 0.5

mm, and it was found in 96% of assessed cadavers.30 However, when

the appearance of the incisive canal on panoramic radiographs
was evaluated, Jacobs et al.34 reported that it was seen only on
15% of the films (n = 545). In contrast, it was observed on 93% of
CT scans.
In the interforaminal area, as
long as the mental foramen and
the anterior loop of the mental foramen (if present) are avoided,
implants can usually be inserted
without too much thought given to
the presence of the incisive canal.
However, if there is an unusually
large incisive nerve canal, a patient
can experience discomfort during
osteotomy development precluding implant placement35 or experience postoperative pain requiring
implant removal.36 Consequently,
consideration should be given to
the size of the incisive canal before
placing implants deeply in the
interforaminal area.

Lingual Foramen and

Lateral Canals
Vascular canals are often present
in the midline and lateral to the
midline of the mandible. Gahleitner et al.37 found
one to five vascular canals per patient. The mean
diameter of the midline canals was 0.7 mm (range,
0.4 to 1.5 mm); the lateral canals in the premolar
area were slightly smaller (mean, 0.6 mm). The lingual foramen was detected in 99% of the mandibles
when evaluating skull dissections.38 However, the foramen was only found on 49% of the periapical films
because the angulation of the x-ray beam affected its
image.
The lingual foramen harbors an artery that corresponds to an anastomosis of the right and left sublingual arteries.39 Small canals with a diameter <1 mm
are unlikely to cause a problem if an osteotomy penetrates into the foramen.37 However, if there is a larger
canal, excessive bleeding could be a complicating factor; thus, consider avoiding implant insertion in the
midline.40 If excessive bleeding from an osteotomy
in this area occurs, guide pins or the implant fixture itself can serve as effective methods of tamponade.
Submental and Sublingual Arteries
The submental artery (2-mm average diameter)41 is
derived from the facial artery, and the sublingual artery
(2-mm average diameter) is a branch of the lingual
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Application of Anatomy

artery.42 The sublingual artery is found above the

mylohyoid muscle and is the major nutrient vessel in
the floor of the mouth.42 The submental artery frequently traverses inferiorly to the mylohyoid muscle
but was noted to pierce through the mylohyoid muscle
in 41% of dissected cadavers.43 Hofschneider et al.41
also reported that the sublingual and submental arteries may course anteriorly in close proximity to the lingual plate, and branches of these blood vessels enter
accessory foramina along the lingual cortex (Fig. 6).
Inadvertent penetration through the lingual cortical
plate into the floor of the mouth while preparing an osteotomy can cause arterial trauma, thereby resulting in
development of a sublingual or submandibular hematoma. It was mentioned that severing an artery 2 mm in
diameter with a probable blood flow of 0.2 ml per beat
(70 beats per minute) can result in 420 ml blood loss in
30 minutes.44 This quantity of hemorrhage can cause
swelling, and the tongue may be pressed superiorly
and posteriorly, blocking the airway, and causing upper airway distress.45,46 The patient requires aggressive medical and possibly surgical management if an
airway crisis develops.
It is also possible to induce hemorrhaging when elevating a flap if a vessel entering an accessory canal is
severed. On the lingual aspect, proper flap elevation
and visualization where the osteotomy is being developed helps to avoid accidental perforations. Bleeding
from the floor of the mouth is first managed by pressure
and then ligation of severed blood vessels.

Figure 6.
Blood vessels entering the lingual cortex of the mandibular anterior
teeth. Arrows point to vascular channels in the lingual cortical plate
of bone.
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Submandibular and Sublingual Fossae

The submandibular fossa is a depression on the medial
surface of the mandible inferior to the mylohyoid line,
and it contains the submandibular gland.47 The sublingual gland is found in the sublingual fossa.48 This fossa
is a shallow depression on the medial surface of the
mandible on both sides of the mental spine, superior
to the mylohyoid line. The submandibular and sublingual fossae must be palpated prior to osteotomy development; if there is a large undercut, the lingual bony
plate can be perforated inadvertently, resulting in
hemorrhaging. Lingual concavities with a depth of
6 mm were reported in 2.4% of assessed jaws (n = 212;
CT scans were used).43 If there is a large undercut, an instrument can be placed into and parallel to the undercut
to visualize and measure the extent of the depression. A
CT scan with radiopaque markers provides the most accurate information. Pertinently, the angulation that the
implant is placed needs to accommodate the undercut
to remain in bone during osteotomy preparation.
The Lingual and Mylohyoid Nerves
The mandibular branch of the trigeminal nerve gives
rise to the lingual nerve.49 This nerve provides sensory
innervation to the mucous membranes of the anterior
two-thirds of the tongue and the lingual tissues. At the
time of implant surgery in the posterior mandible, the
lingual nerve can be injured if the lingual flap is not reflected cautiously. The lingual nerve is usually located
3 mm apical to the osseous crest and 2 mm horizontally from the lingual cortical plate in the flap.50 However, in 15% to 20% of cases, the nerve may be situated
at or above the crest of bone, lingual to the mandibular
third molars.51 In addition, 22% of the time the lingual
nerve may contact the lingual cortical plate.50 To circumvent lingual nerve injury, the elevator should be
used to protect the nerve in the flap, and the tissue
should be managed gently to preclude causing a transient pressure-traction injury. It is recommended that
lingual, vertical releasing incisions be avoided. Furthermore, incisions distal to the second molar should
be made on the buccal aspect of the ridge to provide
additional room for safety, because the lingual nerve
may be lying over the retromolar ridge.51
The mylohyoid nerve is a branch of the inferior alveolar nerve.52 It arises just prior to where the IAN enters
the mandibular foramen. On the deep surface of the ramus, it moves down in a groove to reach and innervate
the mylohyoid muscle and the anterior belly of the digastric muscle. This nerve may also contribute to an inability to attain complete anesthesia due to accessory
sensory innervation to the anterior and posterior mandibularteeth.52,53 In patients who experience discomfort
despite signs of a good block injection, additional infiltration on the lingual aspect in the posterior region
may help to attain more profound anesthesia.53

Greenstein, Cavallaro, Tarnow

J Periodontol October 2008

The Long Buccal Nerve

The buccal nerve is a branch of the mandibular nerve
that is derived from the trigeminal nerve, and it begins
high in the infratemporal fossa.54 It transmits sensory
innervation to the buccal gingiva and mucosa of the
cheek from the retromolar area to the second premolar. It courses between the two heads of the lateral pterygoid muscle, underneath the tendon of the temporalis
muscle, and then under the masseter muscle to connect with the buccal branches of the facial nerve on
the surface of the buccinator muscle. An anatomic variation of the long buccal nerve, called Turners variation, consists of the nerve emerging from a foramen
in the retromolar fossa. When this variation exists,
trauma in this region can cause paresthesia to the adjacent gingiva and mucosa.55
Muscles Attached to the Mandible
There are 26 muscles attached to the mandible.56
There are two single muscles (orbicularis oris and
platysma) and 12 pairs of bilateral muscles, which
are listed in alphabetic order: anterior belly of digastric,
buccinator, depressor anguli oris, depressor labii inferioris, genioglossus, geniohyoid, masseter, mentalis,
mylohyoid, lateral pterygoid, medial pterygoid, and
temporalis. Several of these muscles are of particular
concern to the implant surgeon.
Mentalis Muscle
The mentalis muscle is a paired small muscle that originates in the incisive fossa of the mandible and inserts
into the integument of the chin.57 The muscle fibers
pass in an inferior direction, and upon contraction,
they elevate the lower lip. When a flap is raised in this
region, the entire mentalis muscle should not be released off from the mental protuberances, because
the muscle may fail to reattach well.58 This can result
in an appearance referred to as a witchs chin (double
chin).58 Full-thickness replaced flaps, which do not
reach the inferior border, usually do not affect facial appearance. However, vestibular incisions that sharply
dissect this muscle require special suturing (i.e., the
muscle layer and then the overlying soft tissues).
Mylohyoid Muscle
Two flat mylohyoid muscles form a sling inferior to the
tongue, supporting the floor of the mouth.59 Their origin is the mylohyoid line on the medial aspect of the
mandible, which extends from the symphysis to the
last molar. They insert on the body of the hyoid bone
and overlie the digastric muscles. This muscle is an important anatomic barrier separating the sublingual and
submandibular spaces. The submandibular fossa is
below the mylohyoid muscle, and the sublingual fossa
is superior to the muscle.
Manipulation of the muscle should be performed
only to fulfill clearly defined objectives. In this regard,
sometimes there are situations, such as guided bone

regeneration procedures (GBR), when it is desirable

to advance a flap a large distance to achieve primary
closure. To achieve this, besides flap elevation on
the buccal aspect, it may be necessary to partially dislodge the mylohyoid muscle from its origin to facilitate
lingual flap advancement. First, the lingual flap is elevated to the mylohyoid muscle, and wet gauze can be
pressed apically with a periosteal elevator or the operators finger to achieve blunt displacement of the muscle. Subsequent to surgery, the partially displaced
muscle reattaches without untoward sequelae.
Genial Tubercles (genioglossus
and geniohyoid muscles)
The genial tubercles are small, bony elevations located
on the lingual surface of the mandible. They are found
on either side of the midline close to the inferior border
of the mandible and serve as the point of insertion of the
geniohyoid and genioglossus muscles.60 There are
two superior and two inferior tubercles. The genioglossus originates from the superior genial tubercles, and
the geniohyoid originates from the inferior genial tubercles. The lingual foramen may be found in the middle of the tubercles. The average height of the superior
genial tubercle is 6.17 mm, and its width is 7.01 mm.61
If there is advanced bone resorption in the mandibular
anterior region, the height of the superior tubercle may
coincide with or be higher than the superior level of the
ridge (Fig. 7). When elevating flaps for surgical access,

Figure 7.
A) Because of osseous resorption of the alveolar ridge, the genial
tubercle area (arrow) is now superior to the alveolar ridge.
B) Panoramic x-ray demonstrating genial tubercle area is superior to
alveolar ridge.
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Application of Anatomy

the genioglossus muscle should not be completely reflected off from the tubercles because the tongue may
retract to the posterior part of the throat and obstruct
the airway.58
Depressor Anguli Oris and Depressor
Labii Inferiorus
Two muscles that overlie the mental foramen need to
be displaced when exposing the roof of the foramen:
depressor anguli oris (triangularis) and depressor labii
inferioris (quadratus labii inferioris).62 Once the flap is
elevated past the mucogingival junction, these muscles can be released by using wet gauze to push back
the flap. The wet gauze is used to protect the mental
nerve. Reflection of these muscles does not result in
untoward sequelae.
Buccinator and Orbicularis Oris Muscles
The submucosa is strongly attached to the buccinator
muscle in the cheek region and the orbicularis oris in
the lip area.63 When a surgical procedure is done adjacent to one of these muscles, such as GBR, a soft tissue flap often needs to be advanced to attain primary
closure. In this regard, it may be necessary to create
an incision that provides periosteal fenestration and
penetrates several millimeters into the submucosa,
thereby incising one or both of these muscles to facilitate coronal positioning of the flap.
Masseter Muscle
The masseter muscle consists of two portions: superficial and deep.64 The superficial part arises from the
zygomatic arch and zygomatic process of the maxilla.64 It inserts into the angle and lower half of the lateral surface of the ramus of the mandible. The deep
portion arises from the zygomatic arch and inserts into
the upper half of the ramus and into the lateral surface
of the coronoid process. When the mandibular ramus
area is used as a donor site for bone grafting (i.e., block
graft), part of the masseter muscle is released from the
ramus when the periosteum is elevated in this region.
MAXILLARY STRUCTURES
Thickness of the Gingiva and Palatal Mucosa
The thickness of the gingival and palatal epithelium is
;0.3 mm.65 The gingiva is supported by a lamina
propria (firm connective tissue), whereas palatal epithelium is sustained by a lamina propria and submucosa. Average gingival thickness ranges from 0.53
to 2.62 mm (mean, 1.56 mm),66 and palatal width
varies from 2.0 to 3.7 mm, with a mean of 2.8 mm.67
The best location for harvesting a connective tissue
graft is in the maxillary caninepremolar region.68
Thin grafts may be garnered several millimeters away
from the gingival margin, and thicker grafts can be harvested further away from the gingival margin where the
submucosa is wider.68 The thickest grafts can be ob1840

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tained in the tuberosity region (i.e., 5 mm).68 The width

of the palatal tissue can be estimated by sounding the
bone with a periodontal probe or a needle that has an
endodontic stopper. Graft height is limited by the position of the greater palatine artery, whose location is
subsequently discussed.
Nasopalatine Foramen
The nasopalatine foramen is also referred to as the incisive foramen (Fig. 8).69 Upon flap reflection within
the foramen, two lateral canals are noticeable, which
are called incisive canals or foramina of Stenson. They
transmit the anterior branches of the descending
palatine vessels and the nasopalatine nerves. Occasionally, one to four canals may be present.69 The
nasopalatine foramen is ;4.6 mm wide and is located
;7.4 mm from the labial surface of an unresorbed
ridge.69 The nasopalatine canal (mean length, 8.1
mm) exits the incisive foramen. A large incisive canal
may be an obstacle to implant placement in the central
incisor region. When a large canal was present, Artzi
et al.70 displaced its contents (moved it over without
elimination) and placed an implant. In contrast,
Rosenquist and Nystrom71 enucleated the canal, inserted a bone graft, and subsequently placed an implant. It is also often possible to angle an implant
and avoid the canal.
When performing surgery in the nasopalatine area,
some clinicians create a crestal incision labially
around the incisive papilla to avoid transecting the
contents of the nasopalatine canal.72 An incision
through the canal region does not usually have a detrimental affect; however, it occasionally results in
some numbness of the anterior palatal tissue.
Infraorbital Foramen
The infraorbital nerve and blood vessels emerge from
the infraorbital foramen. The foramen is usually located directly under the pupil of the eye on the inferior
portion of the infraorbital ridge, and it can be palpated

Figure 8.
Incisive foramen exposed (nasopalatine canal [arrow]).

J Periodontol October 2008

through the skin of the cheek. The infraorbital nerve is

found 5 mm below the inferior portion of the infraorbital
ridge,73 and it can be injured during surgery. It is a significant landmark, and intraoral flap elevation should
cease several millimeters inferior to it. The average
height of the maxillary sinus is 36 to 45 mm;74 therefore, a lateral window extending ;15 mm from the alveolar ridge crest usually avoids encroaching on the
infraorbital nerve. However, if advanced resorption
of the maxilla transpired, vigilance needs to be exercised when elevating a flap to avoid damaging the infraorbital nerve.
Greater Palatine Foramen
The posterior maxilla needs to be treated cautiously in
the region of the greater palatine foramen. The greater
palatine artery and nerve emerge from the foramen
and traverse the palate anteriorly. The foramen was
found opposite the third molar in 86% of cases, between the second and third molar in 13% of cases,
and opposite the second molar in 1% of cases.75 Other
investigators76 noted that the foramen was detected
by the third molar in 55% of cases, between the second
and third molar in 19% of cases, opposite the second
molar in 12% of cases, and distal to the third molar in
14% of cases.
The foramen is located halfway between the osseous
crest and the median raphe. Wang et al.77 reported a
mean distance of 16 mm from the center of the greater
palatine foramen to the mid-sagittal plane of the hard
palate. Severing the palatal artery close to the foramen
can present a problem, because it can retract into the
bone, which precludes ligating it. The precise location
of the foramen can be determined prior to flap elevation
by sounding the bone with an anesthetic needle.
Blood Supply in the Maxilla
The internal maxillary artery (maxillary artery) arises
from the external carotid artery behind the neck of the
mandible and provides branches to several regions of
the face: mandibular, pterygoid, and pterygopalatine.78 Surgery in the maxilla can involve arteries in
the pterygopalatine region: descending palatine artery, sphenopalatine artery terminal branch, infraorbital artery, posterior superior alveolar artery, and
the artery of pterygoid canal.
GREATER PALATINE ARTERY
The descending palatine artery emerges from the
greater palatine foramen and traverses anteriorly in a
groove on the medial side of the hard palate to the incisive canal.79 The end branch of the artery enters the
incisive canal to anastomose with the nasopalatine
branch of the sphenopalatine artery. Monnet-Corti
et al.80 reported that the distance from the gingival
margin to the greater palatine artery ranged from
12.07 2.9 mm in the canine area to 14.7 2.9 mm

Greenstein, Cavallaro, Tarnow

at the mid-palatal aspect of the second molar level.

With regard to the greater palatine artery, it is prudent
to assess the height of the palatal vault to establish
the extent to which a surgical procedure can be performed (e.g., harvesting a connective tissue graft) without damaging the artery. It is advantageous to leave
2 mm between the artery and the end of the surgical incision.81 Based upon the shape of the palatal vault, it is
possible to estimate how far the palatine artery is from
the cemento-enamel junction: low vault (flat) = 7 mm,
average palate = 12 mm, and high vault (U-shaped) =
17 mm.81 The mean palatal vault height for males
and females is 14.9 and 12.7 mm, respectively.81
When performing a connective tissue graft, a splitthickness palatal flap, and so forth, the surgeon should
be ready to manage accidental injury to the greater
palatine artery. If the artery is deemed to be close to
the site of surgery, it may be advantageous to place
deep sutures to lasso and ligate the greater palatine
artery distal to the surgical site prior to initiating therapy. If the artery is damaged, this step may preclude
hemorrhaging. To manage bleeding from a damaged
blood vessel, apply pressure, and clamp the palatal
flap where the incision was made with a hemostat. If
the bleeding vessel is visible, ligate it, or apply electric
cautery. Additional deep sutures are needed if the
bleeding vessel is not visible.
SPHENOPALATINE ARTERY
The sphenopalatine artery emerges from the sphenopalatine foramen and enters the back part of the superior
meatus of the nose.79,82 It gives rise to the posterior and
medial lateral nasal branches. The former spreads forward over the conchae and anastomoses with nasal
branches of the descending palatine and ethmoidal arteries. The posterior medialnasalbranches supply blood
to the posteromedial and posterior wall of the maxillary
sinus. When doing a sinus lift, caution must be exercised
to avoid damaging these vessels if the procedure is being
extended to the posterior wall of the sinus.
INFRAORBITAL AND POSTERIOR SUPERIOR
ALVEOLAR ARTERY
The infraorbital artery provides branches to the anterior part of the sinus. These vessels anastomose with
vessels of the posterior superior alveolar artery within
the buccal plate of bone (intraosseous artery) and in
the buccal tissues (extraosseous artery). The intraosseous artery is <16 mm from the crest of the ridge in
20% of cases, and it may need to be managed during
lateral window preparation.83 If the intraosseous artery
is severed, apply pressure with an instrument to the
hemorrhaging site, or it can be touched with a cautery
unit (e.g., Bovie). If a lateral window was created,
elevate the membrane, and compress the bone with
a mosquito hemostat, thereby collapsing the
1841

Application of Anatomy

hemorrhaging blood vessel (Fig. 9). On occasion, it is

necessary to continue preparing the window, despite
the bleeding, until the membrane is elevated and the
bone can be clamped. The assistant should hold the
suction tip next to the bleeding site to preserve good visibility. When the intraosseous artery is severed on the
mesial aspect of the lateral window, it probably is also
injured on the distal aspect. Therefore, the clinician
may need to deal with bleeding on both sides of the lateral window. If a CT scan reveals the presence of an intraosseous artery before starting the lateral window, and
it is possible to circumvent it, develop the lateral window
inferior to the artery, and elevate the membrane internally in a superior direction. However, reasonable access must be achieved, because a poorly located
lateral window can lead to a non-optimal sinus lift outcome. Another technique that can be used to isolate the
artery and not injure it during creation of the lateral window uses a piezosurgery unit (ultrasonic) (Fig. 10).84

Volume 79 Number 10

Figure 10.
Piezosurgery was used to create a lateral window and isolate the
intraosseous artery without inducing hemorrhaging.

Anterior Nasal Spine

Under the nose, in the midline, at the lower margin of
the anterior aperture, there is a sharp bony process
formed by the forward elongation of the maxillae that
is referred to as the anterior nasal spine (Fig. 11).85 It is
used as a landmark when elevating a large flap in the
premaxilla in preparation for flap advancement. Care
must be exercised when extending flap elevation beyond this point because the tissue is thin, and it is possible to penetrate through the tissue into the nose. The
bony rim of the nares is referred to as the piriform rim.
Maxillary Sinus
The maxillary sinus (antrum of Highmore) is pyramidal in shape and is the largest paranasal sinus. Typical
average dimensions of the sinus are height, 36 to 45 mm,
width, 25 to 35 mm, and length, 38 to 45 mm.74 The

Figure 11.
Anterior nasal spine (arrow). It is located under the nose, in the midline,
at the lower margin of the anterior aperture. It is a sharp bony process
formed by the forward elongation of the maxilla.

Figure 9.
If the lateral window for a sinus lift is created and an intraosseous
artery hemorrhages, move the membrane laterally and compress the
bone with a mosquito hemostat to occlude the hemorrhaging blood
vessel. Arrow points to location where hemostat is occluding the blood
vessel.
1842

Figure 12.
CT scan. The ostium (arrow) is the opening from the maxillary sinus
into the middle meatus of the nose.

Greenstein, Cavallaro, Tarnow

J Periodontol October 2008

ostium is the opening from the sinus to the middle meatus of the nose (Fig. 12). It is situated on the superior
aspect of the medial wall of the maxillary sinus above
the first molar. The mean distance from the most inferior point of the antral floor to the ostium is 28.5 mm.86
Thus, when performing a sinus lift, the sinus should not
be overfilled with graft material beyond 15 mm to avoid
potentially blocking the ostium and causing sinusitis.
The maxillary sinus is surrounded by six walls.87 1)
The anterior wall contains the infraorbital nerve and
blood vessels to the anterior teeth. The infraorbital artery gives off the anterior superior alveolar arteries
that supply the sinus mucosa in the anterior section
of the sinus. 2) The superior wall is very thin and
makes up the orbital floor. A bony ridge contains
the infraorbital canal with the nerve and blood vessels.
3) The posterior wall corresponds to the pterygomaxillary region, which separates the antrum from the
pterygopalatine fossa. It contains the posterior superior alveolar nerve and blood vessels, including the
pterygoid plexus of veins and internal maxillary artery. 4) The medial wall separates the sinus from the
nasal fossa. The maxillary ostium (around first molar
area) drains into the middle meatus of the nasal cavity.
5) The sinus floor may extend between the roots of
the maxillary molars. The floor may be 10 mm below the floor of the nasal cavity. 6) The lateral wall
forms the posterior maxillary and zygomatic process.
This wall provides access for the sinus graft procedure.
The medial wall derives its arterial supply from nasal mucosal vasculature. This comes from branches
of the sphenopalatine artery: posterior lateral nasal
and posterior septal branches. The frontal, lateral,
and inferior walls derive their arterial supply from
the osseous vasculature (infraorbital, facial, and palatine arteries). The medial sinus wall drains through
the sphenopalatine vein. All other veins drain through
the pterygomaxillary plexus. Innervation is provided
by nasal mucosa nerves and the superior alveolar
and infraorbital nerves.
Septa (Underwoods clefts) have been located in
31.7% of the maxillary sinuses in the premolar area,
and they usually do not compartmentalize the antrum.88 However, they frequently get larger as they
proceed medially. Therefore, during a sinus lift, membrane elevation over partial septa should proceed laterally to medially, because elevation attempted
anteriorly to posteriorly is more prone to create a perforation. To accommodate large or multiple septa during a sinus lift, more than one lateral window can be
created as part of the antral opening.88 In addition,
septa are a concern if an osteotome sinus floor elevation procedure is planned because it is difficult to infracture the subantral floor under them.
There are several other issues of interest regarding
the management of the maxillary sinus area. If diagnos-

tic imaging indicates that the inferior wall (alveolar

ridge) or the lateral wall of the sinus has a bony fenestration, a split-thickness flap needs to be developed over
these defects to avoid tearing the Schneiderian membrane when the flap is elevated (Fig. 13). Subsequently,
as part of the membrane release, the residual tissue over
the bone defects must be pushed into the sinus, because
the sinus membrane cannot be separated from the soft
tissue that was lodged in the osseous defects.
During a lateral window preparation, if a tear in the
Schneiderian membrane occurs and it is a relatively
small defect, the opening can be patched with a collagen barrier.89 However, when a tear occurs along the
periphery of the window and it is difficult to reengage
the membrane, before the tear elongates, extend the
osteotomy several millimeters in bone away from the
original site. Remove the bone over the membrane
to attain better visibility and accessibility, and reengage the membrane where it is not torn (Fig. 14).
The normal width of the Schneiderian membrane is
generally 0.3 to 0.8 mm.90 However, it can appear

Figure 13.
CT scan. There is a fenestration (arrow) in the inferior wall of the sinus.
When a sinus lift is done, after a split-thickness flap is elevated, the
tissue in the fenestration is pushed into the sinus because the
membrane and the tissue are fused.

Figure 14.
Perforation of the membrane along the periphery of the lateral
window. To reengage the membrane and avoid tearing of the
membrane, more bone is removed to expose more membrane (arrows).
1843

Application of Anatomy

thicker if there is chronic inflammation resulting in

hyperplasia. If the membrane is very thick, consider
obtaining an ear, nose, and throat consult before proceeding with implant placement or a sinus lift.
Nerve Innervation in the Maxilla
The sensory nerves of the palate are branches of the
maxillary nerve.91 The greater palatine nerve innervates the gingiva, mucous membranes, and most of
the glands of the hard palate.91 The nasopalatine
nerve supplies the mucous membranes of the anterior
hard palate. The lesser palatine nerves supply the soft
palate.91 The infraorbital nerve innervates the mucosa of the maxillary sinus; the maxillary incisors, canine, and premolars; the maxillary gingiva; the inferior
eyelid and conjunctiva; part of the nose; and the superior lip.92 The posterior superior nerve supplies the
gingiva and mucous membranes in the posterior maxilla, sinus, and molar teeth.91
CONCLUSIONS
Familiarity with the anatomic structures pertaining to
dental implantology is critically important. Preplanning and review of anatomy before surgical procedures can help to avoid problems. However, certain
anatomic structures may be problematic with respect
to treatment planning. In this regard, many of the
shortcomings of two-dimensional radiography for
treatment planning can be eliminated with the use
of three-dimensional imaging. In particular, if the
mandibular or mental nerves position is not clear
or if it is unclear how much bone is present for implant
placement, a CT scan should be ordered. Similarly,
CT scans are an important diagnostic aid in predetermining the dimensions of the maxillary sinus and
the presence of unexpected findings (e.g., septa, tumors, and intraosseous arteries). A general rule to
follow is, if you are wondering if you need a CT scan,
order one. Finally and importantly, proper training
should be obtained to provide advanced surgical
procedures.
ACKNOWLEDGMENT
The authors report no conflicts of interest related to
this review.
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Correspondence: Dr. Gary Greenstein, 900 W. Main St.,
Freehold, NJ 07728. Fax: 732/780-7798; e-mail: ggperio@
aol.com.
Submitted February 10, 2008; accepted for publication
March 21, 2008.