Background and objectives: Dental and Maxillofacial radiology has long played an exciting and critical diagnostic role, never truer than now with the rapidly expanding array of imaging modalities. Conventional radiographs for third molar evaluation provide information only in two dimensions and therefore spatial orientation of the tooth along with the surrounding structures becomes difficult implying the use of Cone Beam Computed Tomography (CBCT) and Digital Volumetric Tomography (DVT).

Methods: A prospective study was carried out to assess the risk factors associated with the impacted third molar on routine radiographs (IOPA and OPG) in relation to the IAC. The findings from these radiographs were then correlated with the CBCT/DVT findings with JP Rood’s criteria as the baseline.

Results: X-ray IOPA, OPG and CBVT received a median rating of 5 (Poor), 3 (Sufficient) and 1 (Excellent) in the vertical position whereas for the horizontal plane they received a median rating of 5 (Poor), 5 (Poor) and 1 (Excellent) respectively. Statistically highly significant difference was seen among the groups in both the horizontal ( p < 0.001) and vertical ( p < 0.001) plane. X-ray IOPA and OPG failed to detect the horizontal position of the IAC in relation to the roots of third molar in all the cases.

Conclusions: CBVT scan provides accurate information regarding the size and shape of IAC, the inclination of impacted mandibular third molar and the distance and location of the mandibular canal to the impacted tooth in the bucco-lingual and infero-superior dimension. Darkening of the roots, loss of cortication and the interruption of the white line of the IAC can be considered as important high risk factors for intimate root–nerve relationship and intraoperative exposure and mutilation of the inferior alveolar nerve in routine radiographs.

Key words : mandibular third molar; IAC; IOPA; OPG; CBVT/DVT