Cross-sectional tomography. A diagnostic technique for determining the buccolingual relationship of impacted mandibular third molars and the inferior alveolar neurovascular bundle.

Twenty-two patients with 31 impacted mandibular third molars were examined with a new, precise, cross-sectional tomographic technique to assess the radiographic size, shape, branching pattern, location, and degree of cortication of the mandibular canal, and the inclination of impacted mandibular third molars in the buccolingual plane. The mandibular canal, including bifid canals, was accurately identified in 30 cases (96.8%). The cross-sectional appearance of the canal was an uncorticated, or partially corticated, radiolucent oval that measured on average (+/- SD) 2.9 +/- 0.7 x 2.5 +/- 0.6 mm in diameter. It was located more frequently (45.2%) on the buccal aspect of the impacted mandibular third molar. About 60% of the mandibular canals notched the inner cortical plate of the mandible or the third molar root surface. Cystic expansion and quantification of cortical bone destruction were readily assessed by this technique. It was concluded that diagnostic information obtained from cross-sectional tomograms significantly aids the oral and maxillofacial surgeon during the preoperative diagnostic workup and that the radiation risks are comparable to those of other accepted localization techniques.