Detection of the apical lesion and the mandibular canal in conventional radiography and computed tomography

The purpose of this study was to compare the information gathered from dental radiography and high resolution computed tomography (CT) scans with regard to the detection of the endodontic lesion and its relation to the important neighboring anatomic structures such as the mandibular canal.

Fifty patients with a persistent apical lesion referred for endodontic surgery were selected. The teeth involved were 6 mandibular premolars and 44 mandibular molars. Eighty roots were evaluated. For each case 1 CT scan and 1 periapical radiograph were taken. The apical lesion and the mandibular canal were evaluated for possible identification in CT scan or radiograph. The presence of the lesion was correlated to the findings during the surgical procedure. The CT scans of the involved roots were further evaluated with regard to the bone thickness and differentiation between cancellous and cortical bone. The position of the lesion/root within the mandible was studied in all dimensions.

All 78 lesions diagnosed during surgery were also visible with the CT scan. In contrast, only 61 of the lesions were noted by conventional radiographs. The mandibular canal could be identified in 31 cases in dental radiographs, whereas in the oblique cuts of the corresponding CT scans the mandibular canal was detected in all patients. The amount of cortical and cancellous bone and the bone thickness as well as the three-dimensional extent of the lesion could only be adequately interpreted in CT scans.

The use of CT provides additional, beneficial information not available from dental radiographs for treatment planning in apical surgery of mandibular premolars and molars. When the mandibular canal cannot be detected in dental radiographs or is in close proximity to the lesion or root apex, CT should be considered before endodontic surgery. The presence, extent, and location of the lesion and its relation to the mandibular canal can be predictably evaluated in a CT scan of the area.