Diagnostic reliability of panoramic radiography and spiral computed tomography in evaluating topographic relationship of impacted mandibular third molar with inferior alveolar canal

Abstract

Introduction: The inferior alveolar canal is described as a dark linear shadow with thin radiopaque superior and inferior borders cast by the lamella of bone. Conventionally, preoperative assessment is performed by orthopantomogram (OPG). Spiral computed tomography (CT), allows the clinician to localize and determine the relation of the impacted tooth and the inferior alveolar neurovascular canal (IANC) in three dimensions. Objectives: To describe the anatomical and morphologic variation of IANC as it appears in digital OPG and to correlate its relation with IANC on the CT. Materials and Methods: 100 patients were subjected to OPG and were studied for anatomic and morphologic variation. Eleven patients with mandibular impacted third molar in close proximity to the IANC were further subjected to CT examination. Results: Linear type was the commonest on the left side (39.5% in females and 41.9% in males) and elliptical type on the right side (52.6% in females and 45.2% in males). Morphologic variation showed bifid canal present in only 1 (1.6%) male on the left side. On the left side, narrowing of canal was seen in 4 (100%) teeth on OPG, in which 3 (75%) teeth showed 0 mm with cortical break in the CT. Three (100%) teeth showing interruption of white line (superior radiopaque border of IANC) on the OPG also showed 0 mm with cortical break in the CT. On the right side, 2 (100%) teeth showing narrowing of canal on the OPG correlated with 0 mm with cortical break in the CT and 1 (100%) tooth showed interruption of white line which correlated with 0 mm with cortical break in the CT. Conclusion: The comparison between the OPG patients and the CT patients (selected using the Roods criteria from the OPG patients) showed statistically significant value for narrowing of canal and interruption of white line with 0 mm loss of cortication in CT.