multiple mandibular nerve canals: radiographic observations and

VOLUME 38 • NUMBER 9 • OCTOBER 2007 781

QUINTESSENCE INTERNATIONAL

The mandibular canal, or the inferior alveolar

canal, transmits the inferior alveolar nerve, a

branch of the third division of the fifth cranial

nerve (trigeminal nerve), and the associated

vessels. The canal typically extends from the

mandibular foramen to the mental foramen.

The terminal dental and incisive branches

leave the inferior alveolar nerve within the

canal to supply the teeth and adjacent struc-

tures. A terminal branch leaves the canal at the

mental foramen to become the mental nerve.1

Occurrence of bifid mandibular nerve

canals is very rare, and its reported inci-

dence is less than 0.9%.1 Chavez-Lomeli and

colleagues2 suggested that during embryon-

ic development there may be 3 inferior den-

tal nerves innervating 3 groups of mandibu-

lar teeth. Later they fuse to form a single

nerve. Incomplete fusion of these nerves can

explain the presence of bifid or trifid nerve

canals3 in some patients.

It is important for clinicians to recognize

the presence of bifid canals on panoramic

radiographs and modify the dental treatment

accordingly. This article describes 5 cases of

bifid mandibular nerve canal and 1 case of

trifid mandibular canal and discusses their

radiographic diagnosis and clinical anesthet-

ic, orofacial surgical, and prosthetic implica-

tions in dental practice.

CASE REPORTS

Case 1A 35-year-old woman was referred for a

panoramic radiograph (College of Dental

Sciences [CODS], Manipal, India) to evaluate

periodontal bone loss. The radiograph

revealed generalized loss of crestal cortica-

tion along with significant bone loss and a

bifid mandibular canal on the left side (Fig 1).

Multiple mandibular nerve canals: Radiographic observations and clinical relevance.Report of 6 casesAjit Auluck, MDS1/Keerthilatha M. Pai, MDS2/

Muralidhar Mupparapu, DMD, MDS3

Variation in the normal anatomic pattern of the inferior alveolar nerve canal such as bifid

or trifid mandibular nerve canal is one of the reasons for local anesthetic failure in dental

practice. The present article reports 5 cases of bifid mandibular nerve canal and 1 case of

trifid mandibular canal and discusses their diagnostic criteria, radiographic features, and

clinical implications in dental practice. The objective of this review is to help clinicians

identify bifid and trifid mandibular canals on panoramic radiographs and subsequently

use the information in the modification of dental treatment planning. Once the multiple

canals are identified, the local anesthetic injection technique, prosthetic design, and surgi-

cal procedures can be modified to prevent pain and discomfort during treatment proce-

dures. (Quintessence Int 2007;38:781–787)

Key words: bifid mandibular canal, inferior alveolar nerve, local anesthesia, mandibular

canal, panoramic radiograph, trifid mandibular canal

1Assistant Professor, Oral Medicine and Radiology, Manipal

College of Dental Sciences, Mangalore, India.

2Professor and Head, Oral Medicine and Radiology, Manipal

College of Dental Sciences, Manipal, India.

3Associate Professor and Director, Division of Oral and

Maxillofacial Radiology, University of Medicine and Dentistry of

New Jersey, New Jersey Dental School, Newark, New Jersey.

Reprint requests: Dr M. Mupparapu, Diagnostic Sciences, D-

860, UMDNJ New Jersey Dental School, 110 Bergen Street, PO

Box 1709, Newark, NJ 07101-1709. Fax: 973-972-3164. E-mail:

[email protected]

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782 VOLUME 38 • NUMBER 9 • OCTOBER 2007


Auluck et a l

Case 2A 27-year-old woman presented (CODS) with

a prescription for a panoramic radiograph for

pre–implant placement evaluation. The

radiograph revealed an impacted maxillary

right canine and bifid mandibular canal on

the right side (Fig 2).

Case 3A 30-year-old woman had an overretained

maxillary left primary canine, and the perma-

nent canine was missing. A panoramic

radiograph, obtained (CODS) to investigate

the missing permanent canine, showed an

impacted maxillary left permanent canine and

bifid mandibular canal on the left side (Fig 3).

Case 4A 16-year-old girl who had recently under-

gone orthodontic treatment reported for a

prescribed panoramic radiograph (CODS).

The radiograph showed apical root resorption

of the anterior and premolar teeth as well as a

trifid mandibular canal on the left side (Fig 4).

Case 5A 45-year-old man reported to the Oral and

Maxillofacial Radiology Clinic (New Jersey

Dental School [NJDS], Newark, New Jersey)

from the Oral Diagnosis Clinic seeking gen-

eral dental care. The panoramic radiograph

showed multiple missing teeth in the maxilla

and mandible, caries, residual roots, and

multiple restorations, and the mandibular

nerve was noticed to be bifid bilaterally (Fig

5). The mesial extent of the inferior portion of

the bifid canal could not be traced com-

pletely. It is assumed that it either extends

beyond the tomographic layer mesially or

does not have enough canal space to be

captured as radiolucent on the film.

Case 6A 29-year-old woman was referred to the oro-

facial pain clinic (NJDS) for evaluation of

chronic paroxysmal pain in relation to the

mandibular left third molar region. Despite

treatment with anti-inflammatory medication,

pain was persistent.

Fig 1 Cropped panoramic radiograph demon-strating the bifid mandibular canal on the left side.The duplicated canal is toward the posterior andinferior border of the mandibular angle.

Fig 2 Cropped panoramic radiograph demon-strating the bifid mandibular canal on the right side.




Auluck et a l

To assess the proximity of the impacted

and inverted third molar to the inferior alveo-

lar nerve canal, a computerized tomograph-

ic (CT) scan was obtained. During examina-

tion of the hard tissue anatomy of the region

in the mandibular coronal views in bone win-

dows, the variation in the mandibular canal

was noticed on the left side. The canal

appeared dumbbell shaped superiorly with

an extension inferiorly at its origin, and in the

more anterior sections it appeared separate

(Figs 6a and 6b). The sections in the region

of the mental foramen failed to show addi-

tional evidence of this duplication and prob-

ably were not captured well because of

miniaturization.

Fig 3 Cropped panoramic radiograph showingthe bifid mandibular canal on the left.

Fig 4 Cropped panoramic radiograph showingthe trifid mandibular canal on the left side.

Fig 5 Bilateral bifid mandibular canal. (arrowheads) Primary canal; (arrows) duplicated (bifid) canal.



Auluck et a l

DISCUSSION

The term bifid is derived from the Latin word

meaning cleft into 2 parts or branches. For

the mandibular nerve, this occurs at the level

of the mandibular foramen.3 Various studies

using panoramic radiographs have depicted

the presence of bifid mandibular nerve

canals. Its incidence is considered very low

and is reported to be 0.08%, 0.4%, and

0.9%4,5 in various studies. It is suggested that

bifid mandibular canals occur more fre-

quently in females.1,4 Interestingly, 5 of our 6

cases were in women.

Chavez-Lomeli and colleagues2 suggest-

ed that during embryonic development 3

separate canals fuse to form a single

mandibular canal. The bifid and trifid

mandibular canals seen in the present cases

possibly represent unfused canals that per-

sisted as separate, distinct mandibular

canals. Case 4 is the second reported case

in the literature of a trifid mandibular canal.3

Bifid mandibular canals may show multiple

patterns, and 2 distinct classifications were

proposed by Langlais et al4 and Nortje et al5

(Tables 1 and 2).

Each of the nerve canals is surrounded by

upper and lower cortical boundaries that are

easily visible on radiographs. These nerve

canals originate from the mandibular fora-

men. The cortical boundaries surrounding

the nerve canals can fuse to form a triangular

area of bone. If, on a panoramic radiograph,

a triangle having its vertex at the root of sep-

aration of bifid mandibular canal is seen, it is

a pathognomonic feature indicating the pres-

ence of double canals.1 In cases 1 to 5 where

panoramic radiographs were used, this trian-

gular area of bone was identified on the

radiograph. In case 6, bifid canals were iden-

tified incidentally on a CT scan.

There may occasionally be a false appear-

ance of multiple canals on panoramic radio-

graphs. This can be due to the imprint of the

mylohyoid nerve on the internal mandibular

surface where it separates from the inferior

alveolar nerve and travels to the floor of the

mouth.6,7 The false radiographic appear-

ances can also be due to radiologic osteo-

condensation caused by the insertion of the

mylohyoid muscle into the internal mandibu-

lar surface, with a distribution parallel to the

dental canal.1

On panoramic radiographs, to detect bifid

mandibular canals, clinicians must look for

the presence of accessory mandibular fora-

men or the triangular area of bone formed by

the inner cortical boundaries of canals. On a

cross-sectional tomogram or a CT scan (refor-

matted coronal slices), a well-corticated outer

ring of the inferior alveolar canal can be iden-

tified, and the position can be traced in multi-

ple cross-sectional slices until it extends up to

the mental foramen region. The traditional

cortical notching technique can also be used

to identify the canal on CT studies.8 A Denta-

Scan (GE Healthcare) or a SIM-PLANT

(Materialise) software programs can be used

to obtain the dental CT reformatted images.8


Fig 6a Coronal CT view of the mandible in bonewindow demonstrating the bifid mandibular canalimmediately beneath the impacted and invertedmandibular left third molar.

Fig 6b A more posterior coronal CT section of themandible in bone window, showing the mandibularcanal beneath the impacted left third molar. Notethe area of confluence just before the canal sepa-rates into 2 different canals.




Auluck et a l

Identification of the second or third canal

is an important task for the practicing clini-

cian because of its implications on local

anesthetic outcomes. In the authors’ experi-

ence, the inferior alveolar nerve can appear

in various anatomic positions. The nerve

may start out as separate canals within the

ramus of the mandible only to fuse at the

molar region. From there it runs a common

course until the region of the mental fora-

men. This is the most common and easily

identifiable pattern with the triangular bony

island between the 2 canals. It is likely that in

patients with bifid or trifid canals the branch-

es of the nerve run parallel courses within

the body of the mandible until the mental

foramen and possibly end up giving rise to a

secondary mental foramen.

Based on this anatomic variation, an algo-

rithm (Table 3) was developed for a quick

identification of these canals on the

panoramic radiographs, selection of

advanced radiographic procedures, and to

help in the decision-making process. One

should remember that panoramic radio-

graphs and cross-sectional tomograms

should not be prescribed for identification

purposes of these canals alone. If there is

already an indication for obtaining the

panoramic radiograph, either to identify the

position of the tooth in question or to visual-

ize the pathosis that was not completely

seen on an intraoral periapical or occlusal

film, then the radiograph can be examined

for the presence of the mandibular canals.

Inadequate anesthesia is the most com-

mon problem encountered in patients with

bifid mandibular nerve canals. There is no

specific pattern of division or duplication of

the nerve canals.9 This makes it difficult to pre-

dict the efficacy of inferior alveolar nerve

block injections. Inadequate anesthesia of the

region supplied by the mental nerve may be a

problem because 2 separate mental foramina

may exist and the anesthetic solution may

have affected only 1 of the 2 neural bundles.

In cases of bifid canals, a high inferior

alveolar nerve block, such as the Gow-Gates

technique, can be used wherein the anes-

thetic solution is deposited around the trunk

of the mandibular nerve. This technique

simultaneously anesthetizes both the buccal

and lingual nerves along with anomalous or

minor divisions of the mandibular nerve.1,6,9,10

Type I Consists of unilateral or bilateral bifid mandibular canals extending to the third molar or immediatesurrounding area.

Type II Consists of unilateral or bilateral bifid mandibular canals extending along the course of the maincanal and region within the ramus or body of the mandible.

Type III Combination of first 2 categories. Consists of a bifid canal extending to the third molar or surround-ing area or 1 side, as in type 1, and a bifid canal extending along the course of the major canalregions within the ramus or body of mandible in the other side, as in type 2.

Type IV Consists of 2 canals, each of which originates from a separate mandibular foramen and then joinsto form 1 canal.

Table 1 Langlais et al4 classification of bifid mandibular canals

Type I (Most common) Duplicate canals originating from a single mandibular foramen; the canals are usu-ally the same size.

Type Ia The lower canal is smaller. Type Ib The upper canal is the smaller of the 2 canals.Type II A short upper canal extending to the second or third molar areas.Type III (Least common) 2 canals of equal size, arising from separate foramina that join in the molar area.Type IV A double canal variation in which the supplemental canals arise from the retromolar pad area and

join the main canals in the retromolar areas.

Table 2 Nortje et al5 description of the patterns of duplication of mandibularcanals




Auluck et a l

Gow-Gates technique requires maximal

mouth opening and hence, in patients with

restricted mouth opening, the Akinosi tech-

nique can be used to administer local anes-

thesia.9,10 In both these techniques, since the

needle is inserted at a higher level, potential

damage to the maxillary artery and the ptery-

goid plexus exists, and care should be taken

to avoid the injury.10 These techniques

should be used only when there is definitive

radiographic evidence of multiple mandibu-

lar canals and when conventional inferior

alveolar nerve block fails to provide ade-

quate anesthesia.

Bifid or trifid mandibular canals contain

neurovascular bundles.3,11 This fact has impor-

tant surgical implications. During third molar

extraction, extensive care must be taken

because the tooth may infringe on or be with-

in the canal itself, increasing the risk of nerve

damage. Failure to recognize extra canals

can also result in postextraction complica-

tions such as traumatic neuroma, paresthe-

sia, and increased postoperative bleeding.6

Implication for theMandibular Identification Procedures Implications for general dentist or canal features to confirm local anesthesia the implant dentist

Table 3 Diagnostic algorithm for multiple mandibular canals with treatment-planning implications

Appearance ofthe radiolucent,single canal withsuperior and infe-rior well-corticatedborders bilaterally

Two distinct radio-lucent canals, oneabove another,separated usuallyby an island ofmedullary bone

Two distinct radio-lucent canals separated by auniform amountof medullary bone

Three distinct radiolucent canalsseparated byislands of medul-lary bone; allcanals have corti-cated boundaries

Single canal

Double canalsthat are fusedposteriorly

Double canalsthat remain sepa-rate until the men-tal foramen region

Triple canals thatare fused posteri-orly or remainseparate until themental foramenregion

None necessaryunless a root-formimplant is beingplanned

A cross-sectionaltomogram or CT isrecommended ifan implant isplanned in theregion

Cross-sectionaltomogram/CT recommended

Cross-sectionaltomogram/CT recommended

None

Usually none if theinferior alveolar blockis given at a higherlevel (before the nerveenters the canal)

Use caution whileperforming dentalsurgery in the regionsupplied by the mental nerve; if amental nerve block isineffective, an inferioralveolar block is recommendedUse caution whileperforming dentalsurgery in the regionsupplied by the men-tal nerve; if a mentalnerve block is ineffec-tive, resorting to a fullinferior alveolar nerveblock is a better wayto achieve optimallocal anesthesia

None

Position of the canalsmay be somewhatsuperior; use cautionwhile assessing theposition of the canalsbefore implant place-ment implantsAdditional cross-sectional CT may benecessary

Use caution whileassessing the bonefor implant place-ment; additionalcross-sectional CTmay be necessary;use caution whiletreatment planningimplants both anteriorand posterior to themental foramen;additional cross sectional CT may be necessary




Auluck et a l

Epker12 suggested that in surgical proce-

dures such as mandibular osteotomy, it is

necessary to protect the vascularity of the

mandible. Hence, the presence of additional

neurovascular bundles adds to the complex-

ity of surgical procedures. Furthermore, in

cases of trauma, all mandibular fractures

should be handled with care to ensure that

the neurovascular bundles line up exactly, to

avoid impingement when fracture is

reduced. Alignment of the fractured frag-

ments becomes more difficult when the sec-

ond neurovascular bundle is located in a dif-

ferent plane.6 Therefore, while planning the

surgical procedures, the dental surgeon

must look for radiographic evidence of such

an anomaly, determine its location, and mod-

ify the surgical techniques accordingly.

As alveolar bone resorbs in the proximity

of the mental foramen, patients with a

mandibular prosthesis experience pain

because of the pressure on the neurovascu-

lar bundle. In cases of bifid mandibular canal

with branches extending to the third molar

and retromolar pad areas, such a problem

can be encountered.6 Therefore, recognition

of this possible anomaly will allow the clini-

cian to modify the prosthetic design and

impression techniques.

Another important aspect of duplication

of the mandibular canals concerns the iden-

tification of the neurovascular bundles pre-

cisely before placement of any root-form

implants. The duplicate canals may or may

not be visible on head and neck radio-

graphs; it is possible that the bone in cross

section can be evaluated more easily using

either a complex motion tomography, cone

beam CT, or conventional CT utilizing dental

reformation software.13

Awareness and detection of bifid canals is

of considerable interest to the general den-

tist. Careful radiographic observation can

help the clinician recognize this anomaly,

achieve appropriate local anesthesia, and

modify dental treatment accordingly.

Identification of the multiple mandibular

canals also will help the clinician in the plan-

ning and placement of root-form implants

within the mandibular body.

ACKNOWLEDGMENT

The authors would like to thank Dr Gary Heir, professor,

Department of Diagnostic Sciences, University of

Medicine and Dentistry of New Jersey, New Jersey

Dental School, Newark, for allowing us to use the mate-

rial in case 6.

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