Position of mandibular third molar to inferior alveolar canal using cone beam computed tomography: a new classification

Background: Various imaging modalities have been used by clinicians in the preoperative assessment of the third molar position. The aim of this study is to initiate and confirm a new classification for the inferior alveolar nerve (IAN) injury with respect to positional relation between the tooth and the inferior alveolar canal (IAC) using Cone Beam Computed tomography (CBCT). Material and Methods: Mandibular CBCT scans were assessed randomly and were reviewed retrospectively. Patients with complicated mandibular third molars cases were then selected for the study. Complicated mandibular third molars refer to those which met at least one of the following criteria i.e., partially or fully impacted, contact or interrupt the inferior alveolar canal, considerable obstruction of the longitudinal axis of adjacent tooth during teeth eruption. The new classification system was established based on: the positional relation of tooth to the IAC in the coronal/ axial reconstructions of the CBCT. Results: Of these cases, TYPE I: Buccal and Abutting (28%), TYPE II: Lingual and Abutting (48%), TYPE III: Root Apex and Abutting (14%) (When the nerve is <5mm from the root apex), TYPE IV: Intraradicular (10%). TYPE II was the most common type of classification (48%) while TYPE IV was the least common type (10%). Conclusions: The presented new classification system which is based on positional relation between the tooth and the IAC is proved to be applicable in detecting mandibular third molar with higher risk of IAN injury. Hence this will aid as a good guidance for the appropriate treatment design.