Comparison Between Panoramic and Cone Beam Computed Tomography (CBCT) for Dental Use for the Assessment of Inferior Alveolar Canal in 500 Extracted Third Molars

Abstract

Statement of the Problem: In this study, the positional relationship between the mandibular canal, through which the inferior alveolar nerve passes, and the third molar was observed in detail in patients who underwent CBCT imaging. The same information was obtained from panoramic radiographs and compared. Materials and Methods: The materials used were radiographs of 500 third molars from 366 patients (159 males, 207 females; aged 15 to 79 years, mean 32.5 years) who were treated at the Dept of Oral Surgery, Nihon University School of Dentistry in the 6 years between 1998 and 2004, and who underwent Cone-beam computerized tomography (CBCT) imaging (3DX, MORITA Cop Kyoto Japan, US name 3D Accuitomo). The distance and positional relationship between the third molar and the mandibular canal, buccolingual position, and mandible width were observed using the CBCT images. The positional relationship between third molar and mandibular canal and the status of the white line defining the superior wall of the mandibular canal were observed using panoramic radiographs. Method of Data Analysis: From the contiguous parallel slices of the dental arch (cross-sectional view of the arch) that were acquired, the image in which the third molar and mandibular canal were closest was selected and classified as follows. Classification based on distance: Relationship between third molar and mandibular canal on CBCT images Separated by more than 1 mm (Grade I), separated by less than 1 mm or in contact, and walls of mandibular canal seen as white lines (Grade II), Separated by less than 1 mm or in contact, and walls of mandibular canal not seen as white lines (contiguous with periodontal membrane space) (Grade III). The distance was measured using the 3DX system software (Morita Co, Kyoto, Japan). Classification based on location: Located on buccal side of third molar (B), Mandibular canal in contact with root apex (I), Located on lingual side of third molar (L), Located in the area of the ramus (R). Classification of panoramic radiographic findings: Third molar and mandibular canal in contact or overlapping and Superior wall of mandibular canal seen as a continuous white line (Type A). Third molar and mandibular canal in contact or overlapping and Superior wall of mandibular canal not clearly seen as a continuous white line (Interruptions of the cortical white line) (Type B). Downward displacement of the mandibular canal in the area of the third molar (Diversion of the canal) (Type C). Patients were examined for postoperative dysesthesia of the lower lip. Results: Among the 366 patients (500 teeth) in whom CBCT imaging was performed, the mandibular canal was in buccal position in 252 patients, inferior position in 139 patients, lingual position in 95 patients, and in the ramus region in 14 patients. Based on the distance, 167 patients were Grade I, 194 were Grade II and 139 were Grade III. The panoramic radiographic findings were as follows: Type A; 230 patients, Type B; 175 patients, and Type C; 95. Grade III distances were seen in CBCT images of 28 of 230 (12.1%) patients with Type A panoramic radiographic findings, 30 of 175 patients (17.3%) with Type B findings, and 81 of 95 patients (85.2%) with Type C findings. Postoperative dysesthesia of the lower lip occurred in 5 patients (1.0%), all of whom were classified as Grade III. Conclusion: Diversion of the mandibular canal in the area of the third molar in panoramic radiographic images indicates a tendency for proximity of the third molar and mandibular canal, which would help to determine the risk of dysesthesia after extraction.