682 BIFID MANDIBULAR CANAL SONNEVELD ET AL

Bifid Mandibular Canal: A Case Review

and Retrospective Review of CBCTs
Keith A. Sonneveld, DDS,* Peter T. Mai, MS,† Maritzabel Hogge, DDS, MS, MSMEd,‡ Eun Y. Choi, DMD, MS,§
and Jason E. Portnof, DMD, MD¶

he inferior alveolar nerve (IAN) Purpose: This case presentation noted to have bifid canals. A greater

T is a branch of the fifth cranial

nerve, which splits into 3 divi-
sions intracranially. The third divi-
and retrospective review of cone-
beam computed tomograms is to
evaluate prevalence, classification,
percentage of patients were shown to
have bilateral bifid canals (42.9%)
versus either unilateral side (25%
sion of the trigeminal nerve exits and demographics of bifid mandibu- left, 32.1% right), but is statistically
the skull base at the foramen ovale
lar canals (BMC) to inform practi- insignificant. Prevalence was greatest
and further splits into a number of
branches. The IAN enters the mandi- tioners on this variation and avoid in types 1 and 3 (35.9% and 51.3%,
ble at the mandibular foramen near untoward complications due to fail- respectively, P ¼ 0.000011). Types 2
the junction of the body and the ramus ure to diagnose. and 4 were much less common.
of the mandible, where it courses Materials and Methods: Two Conclusion: BMCs are an
through the mandible, supplying sen- thousand one hundred thirty scans important anatomic variation that
sory innervation to the teeth, gingiva, were evaluated by 2 oral and max- has implications on any mandibular
mucosa, lip, and chin.1–3 It has been illofacial radiologists. BMCs were surgery, including implant surgery.
suggested that the 1 mandibular canal noted and classified according to Just more than 1% of patients have
arises from 3 separate ones, which Naitoh. Demographic data were also this variation, but failure to recog-
fuse in a majority of cases to form 1 collected and analyzed. nize this in a patient can result in
canal.4 Results: Twenty-eight patients poor outcome, as illustrated in the
A clinically significant variation
were noted to have bifid mandibular case presented. (Implant Dent
of normal anatomy of the mandibular
canal is that of a bifid or trifid canal, with an average age of 39 2018;27:682–686)
mandibular canal, which has been years (6 19.5), with no strong sex Key Words: anatomy, paresthesia,
noted in the literature since the predilection. Patients (1.31%) were complications
1970s.5–8 It has been suggested that
problems arise with local anesthe-
sia,9–11 implant placement, third molar extractions, bone grafting pro- of retrospective studies showed that eval-
cedures,12 and even mandibular os- uation of bifid canals based on in situ
*Resident, Department of Oral and Maxillofacial Surgery, Nova teotomies. Detection preoperatively evaluation, panoramic radiographic eval-
Southeastern University-College of Dental Medicine, Fort
Lauderdale, FL.
†Student, Nova Southeastern University-College of Dental
and appropriate planning should sig- uation, multidetector computed tomogra-
Medicine, Fort Lauderdale, FL.
‡Associate Professor, Division of Radiology, Nova
nificantly reduce the likelihood of phy, or CBCT evaluation yielded
Southeastern-College of Dental Medicine, Fort Lauderdale, FL.
§Assistant Professor, Division of Radiology, Nova Southeastern-
complications such as bleeding and a prevalence of 6.46%, 4.20%, and
College of Dental Medicine, Fort Lauderdale, FL.
¶Associate Professor, Department of Oral & Maxillofacial
paresthesia/dysesthesia. 16.25%, respectively.12
Surgery, Nova Southeastern University-College of Dental With the advent of technology, A number of different classification
Medicine, Fort Lauderdale, FL.
detection of these has gone from detec- schemes have been proposed,18 based on
Reprint requests and correspondence to: Keith A. tion with a panoral radiograph to panoramic radiographic findings,3,7,8,19
Sonneveld, DDS, Department of Oral and Maxillofacial medical-grade computed tomography and more recently CBCT findings.20–22
Surgery, Nova Southeastern University-College of
Dental Medicine, 3200 S, University Drive, Davie, FL to cone-beam computed tomogra- Numerous case reports exist describing
33328, Phone: 708-738-1116, Fax: 954-355-5490, phy.12 A wide range of different retro- the cases as incidental findings, before
E-mail: KS2042@mynsu.nova.edu
spective studies exist examining treatment or involving minimal compli-
ISSN 1056-6163/18/02706-682 prevalence,13–17 with prevalence as low cations.9–11,16,23,24 The case presented is
Implant Dentistry
Volume 27
Number 6 as 0.35% and as high as 65%.17 The prev- a complication that is based on a lack of
Copyright © 2018 Wolters Kluwer Health, Inc. All rights
reserved. alence differed significantly with the proper detection before dental implant
DOI: 10.1097/ID.0000000000000819 method of evaluation. A meta-analysis placement.

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SONNEVELD ET AL IMPLANT DENTISTRY / VOLUME 27, NUMBER 6 2018 683

CASE REPORT
The patient is a 33-year-old woman
who presented to the clinic for evaluation
and treatment after placement of a dental
implant in site 30. The patient had
immediate implant placement with allo-
graft and platelet-rich plasma after extrac-
tion of the tooth approximately 3 weeks
before initial evaluation in the clinic. The
patient experienced immediate intense
pain, which was followed with dysesthe-
sia of the lower lip and chin area, which
has improved in the intervening time
before presentation to office.
The patient has no remarkable Fig. 1. Panoramic radiograph on initial evaluation in the clinic, after implant placement. Close
medical history. She takes no medica- examination of the posterior body/ramus area of the right mandible shows some irregularity of
tions at home and denies any drug the cortex of the mandibular canal, indicating a bifid mandibular canal.
allergies. Clinical examination on eval-
uation showed a well-developed, well-
nourished woman, with no significant
extraoral or intraoral edema or ery-
thema. A heavily restored dentition is
noted and implant fixture in the place of
tooth number 30, with no significant
mobility or tenderness associated with
this site. There is hypoesthesia of the
gingiva overlying the site, but overall,
the dysesthesia of her lip reported pre-
viously is absent on evaluation.
The panoramic radiograph is shown
in Figure 1. Close inspection of the right
mandibular body shows what appears to
be a cortical irregularity in the posterior
region that could indicate the presence of
a bifid canal. The patient also provided
CBCT scan CDs, which were evaluated Fig. 2. CBCT volume render showing a transverse accessory canal, which is positioned
by the Nova Southeastern University – superior to the main trunk of the mandibular canal. It is much easier to appreciate the bifid
College of Dental Medicine oral and nature of the canal, as it splits in the posterior body region and passes through the mandible
maxillofacial radiologists who confirmed superior to the main trunk of the canal. This accessory branch ascends toward the crest of the
alveolus in the area of the implant in site 30.
the presence of a bifid canal, which would
be considered type Ib according to Nortje
et al,7 type I according to Langlais et al,19
review. A total of 2130 CBCT scans described by Naitoh (Fig. 4). A type 1
and type 3 without confluence according
were evaluated by oral and maxillofa- or “retromolar canal” is a bifid canal,
to Naitoh et al20 (Fig. 2). The preoperative
cial radiologists at Nova Southeastern which splits in the ramus region and
and postoperative CBCT scans (Fig. 3)
University College of Dental Medicine. terminates in the area posterior to the
show coronal views, which clearly depict
The presence of a bifid mandibular third molar or near the apex of the sec-
2 separate nerve foramina, and the close
canal was noted, as well as canal ond or third molars. A type 2 or “dental
approximation of the implant to the
classification according to Naitoh. canal” splits in the ramus region and
accessory canal.
Other data compiled for evaluation terminates in the area of the second pre-
included age, sex, and laterality. molar or first molar. A type 3 or “for-
Statistical analysis was performed ward canal” splits in the ramus region
MATERIALS AND METHODS to determine the mean age with standard and runs parallel to the main canal and
The study was evaluated by the deviation. A chi-square analysis was terminates near the mental foramen.
Institutional Review Board of Nova performed on the other data to determine Type 4 canals are rare and are similar
Southeastern University and was deter- validity with a P value of 0.05. to the type 3 canals except that they run
mined to be exempt from full review The classification scheme used for buccolingually, termed as a “buccolin-
because of its nature as a retrospective analysis in the present research is gual canal.”

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684 BIFID MANDIBULAR CANAL SONNEVELD ET AL

RESULTS
CBCT scans (2130) were exam-
ined, with a total of 28 patients who
were noted to have bifid mandibular
canals (BMCs), for a total number of 40
BMCs. Patients (1.31%) were found to
have a bifid mandibular canal, and
0.938% of canals scanned were found
to be bifid (Table 1).
The mean age was 39 years with
a standard deviation of 19.58 years
(Table 2).
The percentage of female patients
with BMC was 54%; male was 46%.
This distribution was found to be sta-
tistically insignificant (P value 0.705,
Table 2).
The distribution of laterality was
25%, 32.1%, and 42.9% left, right, and
Fig. 3. A, Preoperative CBCT cross-sectional images at 1.8 mm intervals showing distinctly bilateral, respectively. This was also
separate radiolucency superior to the main trunk of the IAN, which represents the accessory found to be statistically insignificant (P
canal. By tracking this separate canal, it is seen that it closely approximates the root apices of value 0.507, Table 2).
tooth number 30, which informs the treating provider with details important for planning Distribution of classification was
implant surgery. B, Postoperative CBCT showing the dental implant placed within 0.42 mm of
the accessory canal. This close approximation of the implant to the accessory canal violates
shown to be highest in the type 3
the guidelines to keep implant placement farther than 2 mm from the mandibular canal. The category at 51.3%, followed by type 1
recommendation is done to reduce the risk of postoperative sensation disturbances, dis- at 35.9%. Much lower was types 2 and
turbances which occurred for this patient. 4, at 5.1% and 7.7%, respectively.
These findings were determined to be
statistically significant (P value
0.000011, Table 2).

DISCUSSION
This case discusses an unfortunate
complication that occurred as a result of
failure to diagnose a bifid mandibular
canal. In this situation, the initially
treating provider had a CBCT image,
which has shown consistently higher
prevalence than other modes of detec-
tion.12 There is as well evidence shown
that these radiographic studies do
indeed correlate to in situ presence.22
The generally accepted recommen-
dation for implant placement in the
mandible is to stay 2 mm away from
Fig. 4. A, Cropped panoramic reformatted view. Type I, retromolar canal. This shows the
the mandibular canal.25 This recom-
separation from the main trunk in the ramus area, where it ascends superiorly toward the
retromolar area just distal to the third molar. B, Sagittal view. Type II, dental canal. The image mendation is made to avoid complica-
shows the separation from the main trunk of the canal in the ramus area. The image was tions such as anesthesia, hypoesthesia,
unfortunately unable to capture the termination of the accessory branches at the apices of the dysesthesia, and paresthesia. There are
second and third molar. C, Cropped panoramic reformatted view. Type III, forward canal. This multiple different ways to create an
image shows a linear radiolucency that splits from the main trunk of the mandibular canal and insult to the IAN during implant place-
runs along the mandible, ultimately terminating in the apices of the first molar and premolars. ment, including direct and indirect
D, Cross-sectional view. Type IV, buccolingual canal. This type of accessory canal can only be
viewed from the cross-sectional view or, in some cases, axial views. The 2 distinct radio-
insult.26 However, a retrospective study
lucencies are approximately the same diameter, making it difficult to make a determination evaluated implant placement closer
between the main trunk and accessory canal. than 2 mm to the IAN, which showed
no statistically significant difference in

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SONNEVELD ET AL IMPLANT DENTISTRY / VOLUME 27, NUMBER 6 2018 685

Table 1. Prevalence of BMCs associated with a failure to detect this

variation of normal anatomy. In the
Prevalence (%) current age, with the increasing use of
Scans performed 2130 cone-beam computed tomography
Patients with BMC diagnosis 28 1.31 imaging for treatment, it is likely that
Total no. of mandibular canals 4260 the diagnosis of bifid canals will
Bifid canals 40 0.938 become more frequent. The provider
This data table shows the total number of patient scans evaluated, compared with the number of patients diagnosed with a bifid treating the mandible surgically must be
canal, yielding a prevalence. As well, the total number of mandibular canals was evaluated compared with the number of diagnosed vigilant and cognizant of the possibility
bifid canals, yielding a prevalence among all canals.
of a bifid mandibular canal and amend
treatment accordingly.
Table 2. Statistical Analysis
P Value DISCLOSURE
Age The authors claim to have no
Mean 39 financial interest, either directly or
Standard deviation 19.58 indirectly, in the products or informa-
Sex, no. per sex (%) 0.705457 tion listed in the manuscript.
Male 13 (46)
Female 15 (54)
Laterality, no. per sex (%) 0.50734 ROLES/CONTRIBUTIONS
Left 7 (25) BY AUTHORS
Right 9 (32.1) K. A. Sonneveld: Primary Investi-
Bilateral 12 (42.9) gator. P. T. Mai: Secondary Investiga-
Classification, no. per type (rate [%]) 0.000011
tor. M. Hogge: Reading Oral and
Type 1: retromolar canal 14 (35.9)
Maxillofacial Radiologist. E. Y. Choi:
Type 2: dental canal 2 (5.1)
Type 3: forward canal 21 (51.3)
Reading Oral and Maxillofacial Radi-
Type 4: buccolingual canal 3 (7.7)
ologist. J. E. Portnof: Faculty Advisor.
The pool of data was analyzed for mean age with standard deviation, sex predilection, laterality, and type of classification according to
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