Diagnostic imaging study of the relationship between the mandibular third molar and mandibular canal. Use of helical computed tomography for multiplanar reconstruction

We aimed to evaluate the ability of panoramic radiography to reflect the information provided by three-dimensional CT scans of the mandibular third molar and mandibular canal by comparing panoramic radiographs with CT scans. Panoramic radiography was used to evaluate the superimposition of the third molar root apex with the mandibular canal and deflection of the mandibular canal at the third molar root apex. Deflection and compression of the mandibular canal was detected by cine display of cross-sectional images. For each case, panoramic radiographs and Tooth-Pix images of the CT scans were compared. Results showed a higher incidence of mandibular canal deflection with an increase in overlap between the mandibular canal and third molar root apex. In the present study, a bone wall was absent more often in cases in which the mandibular canal traveled on the lingual side than in cases in which it traveled on the buccal side and above the tooth axis. Therefore, it may be necessary to carefully examine morphology as well as anatomic position when analyzing the mandibular canal image. It may be necessary to pay closer attention during tooth extraction when the root apex is below the lower mandibular canal wall, or when widening of the mandibular canal by a considerable portion of the third molar is observed on panoramic radiograph. Therefore, pre-surgical CT may be needed to determine the positional relationship when mandibular canal deflection at the root apex is detected by panoramic radiography. (author)