The mandibular canal (MC) transmits the inferior alveolar nerve (a branch of the mandibular nerve which is the third division of the trigeminal nerve) and the inferior alveolar artery and vein.
The inferior alveolar nerve supplies the mandibular teeth and gives off the mental nerve, which exits the MC through the mental foramen.
Knowledge of the anatomy and location of the MC are essential for successful procedures in the region such as inferior alveolar nerve block, surgical dental extractions especially wisdom teeth, implants placement, etc.1
Anatomical variations of the MC, mostly bifid,2-4 and more rarely trifid,5 have been reported by many authors using different radiographic technologies [panoramic, computed tomography (CT) and cone-beam computed tomography (CBCT)].2-4
This report describes a case of a unilateral bifid MC (BMC) suspected by a panoramic radiograph and confirmed by a CBCT prior to a dental treatment.
A 22-year old male presented to our office for extraction of his wisdom teeth.
On the panoramic, #18 was absent, while #28, #38 and #48 were impacted with mesioangulated inclination (Figure 1).
The apices of #38 and #48 were superimposed on the left and right image of the MC and a BMC was suspected at the left side. A CBCT was requested for further assessment.
On the CBCT examination, and after drawing the canal on both sides, the following were noted: i) on the right side: the MC is located lingual to the root of the #48, in close relationship with the distal root (Figure 2); ii) on the left side: at the exit of the mandibular foramen, appears the usual track of the MC, but distal to him, appears another thinner canal that goes more inferior, closer to the inferior border of the mandible, and join the principal canal at the level of the distal root of #37 (Figures 3 and 4).
At the level of #38, the MC is located lingual to it, in close relationship with its distal and mesial root.
BMC was evaluated by many authors by means of different radiographic techniques.
A higher incidence was reported by Durst and Snow [8.3% (85/1024)].9
Nowadays, with the technological improvement of the imaging techniques such as CBCT, more details are provided and consequently better evaluation. Thus, many studies propose that the incidence of BMC is underestimated with the use of panoramic radiographs alone.9,10
Kuribayashi et al., consider that the incidence of BMC may be superior when using CBCT, since panoramic radiographs are not adequate to detect all canals especially narrow ones. In their study, they reported the prevalence of BMC to be as 15.6% (47/301).4
These findings were consistent with the ones of Klinge et al., who concluded in their study performed on cadavers that panoramic images were unsuccessful to identify the MC in 36.1% of cases,10 and Bogdán et al., who noticed that among their specimens, only 0.2% of BMCs were visible on panoramic radiographs while 19.6% were detectable on dry mandibles.5
On the other hand, on panoramic images, some anatomical structures may mimic BMCs such as the groove of the mylohyoid nerve located on the deep internal surface of the mandible ramus,8,11 or some intra-bony dense trabecular formations.12
This being said, even if routine panoramic radiographs prior to many dental and oral procedures in the region of the MC are largely recommended, they have limitations in exhibiting intra osseous structures consequently when used to assess the existence and the configuration of BMCs. Contrariwise, CBCT is considered more accurate for differentiating true from false BMCs.4,12
Concerning the types of BMCs, many classifications have been suggested by different authors among others Nortjé et al.,2 Naitoh et al.,13 and Langlais et al.3 whose classification remains the most cited in the literature.14
The latter is divided into four types according to their locations and shapes (Table 1).
We believe our present case is still a rare variation.
Although considered a rare anatomical variation, BMC may be found in each patient and must be assessed adequately.
Technological improvement of imaging techniques has provided alternatives for complete and precise evaluations. Among these techniques is CBCT, which provides images in the three planes, offering better information about the MC and the detection/confirmation of BMCs thereby preventing probable complications.