Relation between mandibular third molar and mandibular canal as assessed by three-dimensional Computed tomographic reconstruction.

Mandibular third molars are usually located near the inferior alveolar nerve. Their surgical removal may damage the nerve and cause dysesthesia of the lower lip. Panoramic radiography is often used preoperatively to estimate the distance between the mandibular third molars and the inferior alveolar nerve. However, the buccolingual relation of these structures cannot be determined by this method.Three-dimensional Computed tomography (3 D-CT) is more useful in diagnosis than panoramic radiography. This study was designed to assess the diagnostic value of 3 D-CT.A total of 209 mandibular third molars in 138 patients were evaluated by both 3 D-CT and panoramic radiography. We classified the radiographic relation between tooth roots and the mandibular canal into 5 types. The types were recorded for each panoramic radiograph and 3 D-CT scan.3 D-CT findings: 49 teeth showed Type 1; 45 of 49 teeth showed exposure of the inferior alveolar nerve.Panoramic radiograph findings: 82 teeth showed Type 1; 38 of 82 teeth showed exposure of the inferior alveolar nerve. There was a significant difference between 3 D-CT findings and panoramic radiographic findings (p<0.05).Patients with loss of the superior white line of the canal on panoramic radiographs had a high incidence of nerve exposure during surgery (p<0.005). There was also a correlation between radiographic loss of the superior white line and closeness of the tooth and canal on 3 D-CT (p<0.05). These findings are clinically important.We conclude that 3 D-CT provides clinically useful information with respect to the relation between the mandibular third molars and the mandibular canal.