Diagnostic ability of limited volume cone beam computed tomography with small voxel size in identifying the superior and inferior walls of the mandibular canal

BACKGROUND: The aim of this study was to evaluate the visibility of the superior and inferior walls of the mandibular canal separately using limited volume cone beam computed tomography (CBCT) with small voxel size. METHODS: CBCT cross-sectional images of 86 patients obtained by 3D Accuitomo FPD and reconstructed with a voxel size of 0.08 mm were used for the evaluation. A 30-mm range of the mandible just distal to the mental foramen was divided into three equal areas (areas 1, 2, and 3, from anterior to posterior). Each area contained 10 cross-sectional images. Two observers evaluated the visibility of the superior and inferior walls of the mandibular canal on each of the cross-sectional images in these three areas. The visibility ratio in each area was determined as the number of cross-sectional images with a visible wall divided by 10. RESULTS: In all areas, the visibility ratio of the superior wall was significantly lower than that of the inferior wall. As for variance among the three areas, the ratio was highest in the most posterior area (area 3) and tended to decrease gradually towards the mental foramen for both walls. Cases in which more than two thirds of the superior wall could be identified (visibility ratio of 0.7 or more) in areas 1, 2, and 3 were 44, 62, and 66%, respectively. CONCLUSIONS: The superior wall was significantly more poorly visualized than the inferior wall in all areas examined. The visibility of the superior wall on CBCT images was limited even when a limited volume device with small voxel size was used.