The Validity of the Panoramic Radiography in Evaluating the Topographic Relationship between Mandibular Canal and Impacted Third Molars in Comparison with Cone Beam CT-scan

: Background : The purpose of this study is to compare the validity of panoramic radiography with CBCT (Cone Beam Computed Tomography) in the assessment of the relationship between the mandibular third molar and the mandibular canal.Materials and Methods : In this descriptive-analytical study, 80 mandibular third molars were extracted from 48 patients. On the panoramic radiography (PR) there was a close relationship between the root tooth and mandibular canal in all the teeth. The teeth were classified on the basis of six radiographic markers in panoramic radiographs (superimposition, root opacity/darkening of the roots, root deflection, diversion of the canal, interruption of the cortical border of the canal and narrowing of the canal). Then, the relationship between the markers and presence or absence of contact is CBCT was investigated.Results : The superimposition marker in the interrupted group and group with intact border was significantly higher than the group with no cortical border. The interruption of the cortical border of the canal and increased radiolucency marker were significantly higher in no-cortical border group than the other two groups. As to the other three markers (diversion of the canal, narrowing of the canal and root diversion) due to the low frequency in the 80 teeth, the findings were presented in a descriptive manner.Conclusion : Presence or absence of a radiological sign in panoramic radiography will not properly predict the existence of a close relationship with third molar and it is suggested that in case of tooth-canal overlapping either as a superimposition or as other aforesaid markers, the patient should be referred for CBCT assessment regarding the additional and useful information provided by CBCT.