Bifurcation of the mandibular canal- Radiological appreciation of a rare anatomical variation - Report of 3 cases and review of the literature

The mandibular canal is a single canal that runs in the mandible carrying inferior alveolar neuro vascular bundle and splitting of the mandibular canal into in its course is rare occurrence. With the advent of 3-dimensional imaging modalities like computed tomography or cone-beam computed tomography better visualization becomes possible. As a result, more cases of this nature are being reported in the recent past giving rise to increased prevalence than in the past where two-dimensional imaging like digital panoramic tomography were dominating. This article also appreciates the radiological anatomy of three cases with bifurcation of the mandibular canal incidentally diagnosed in the cone-beam computed tomography and also discusses the clinical significance of this rare anatomical entity.


Introduction
The mandible is a unique piece of anatomy that had amazed both the anatomists and clinicians due to its structure and multitude of functions it performs. The mandible being the second bone to begin ossification in the body ossifies approximately in the 6-7 th week of intrauterine development. [1] Cartilage formation tends to occur as clusters from the Meckel's cartilage and then unify to form a single bone. In both humans and primates, this ossification process completes in the first year after birth. [2] Mandibular canal is formed by the encapsulation of bone during embryogenesis. [2] The mandibular canal originates from the mandibular foramen in the posterior aspect of mandible and terminates at the mental foramen in the anterior aspect of mandible and it carries the inferior dental nerve, artery, and vein. . [1] It is a single canal, running anteriorly, through the trabecular bone, to the level of the alveolus of the mandibular central incisor, near the mental foramen. [1] The canal is wide and narrows towards the medial side. [1,2] It is known that the mandibular foramen can have variations, but rare in nature. [3] It can be in the form of the bifid, trifid, double mandibular canal, and pseudo bifid/double mandibular canal. [3] The reason for these variations in the mandibular canal is related to the embryological formation of the inferior dental nerve (IDN) in the mandible. [4] Radiologically, the mandibular canal is characterized by a radiolucent strip in between two radio-opaque lines, generally, it is a single structure observed in different positions of the mandible and around the mandibular third molar. [3] The incidence of a bifid mandibular canal is dependent on the method of radiological investigation such as Dental panoramic The presence of BMC has many clinical implications and such as knowledge of variations in the course of the mandibular canal is important in lower impacted third molar removal surgery, implant placement in the posterior mandible, orthognathic surgery, when managing the failure of IDN block and as a differential diagnosis in pain in posteriorly resorbed alveolar ridges caused by the pressure exerted by dentures [5]. [6][8]. [9].
Here, we report three cases of BMC which was identified incidentally to appreciate its radiological anatomy and literature to understand this entity.

Case history
In all 3 cases, the bifurcation of the mandibular canal was diagnosed from the referrals for evaluating the risk of Inferior dental canal damage in lower mandibular third molar removal surgery by evaluating the Cone Beam Computed Tomography (CBCT) images.
Details of the 3 cases are summarized in table 1. Table 1 (table 2) According to this classification, our 3 cases belong to type 1, which is the more prevalent type as the division occurs before the root of the impacted mandibular third molar. The identification and understanding of this variation of the mandibular canal is important for a maxillofacial surgeon or plastic surgeon as well, especially when performing bilateral sagittal split osteotomy in the orthognathic surgical correction of the defects of the mandible. [14] Complications such as traumatic neuroma, paresthesia, and bleeding can occur due to the ignorance of this variation. [15] The prevalence of bifid mandibular canal is rare but with the advent of better threedimensional modalities, this premise may be questionable. Further investigations are warranted. The appreciation of the anatomy of this entity is important for the management of the IDN block failures. Also, for performing extraction of impacted lower third molars, placement of posterior implants, and performing bilateral sagittal split osteotomy in orthognathic surgery to prevent IDN canal damage.

Conflicts of interest
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