Assessment of the space for the lower wisdom teeth. Panoramic radiography in comparison with computed tomography.

From 13 patients a computed tomograph (CT-scan) and a panoramic radiograph (Orthophos, program 1, P1) were examined with respect to the spatial conditions of the lower wisdom teeth. In the panoramic radiograph the available space for the third molars of the lower jaw was determined by calculating the ratio (Q) of 2 distances: the mesiodistal crown diameter and the retromolar space. In the axial CT 3 different positions of the third molar were distinguished: third molar located anterior to the ramus mandibulae = sufficient space, partially within the ramus = restricted space, totally within the ramus = deficient space. These positions were compared with the findings in the panoramic radiograph, firstly in relation to the ramus and secondly in relation to a line (L) perpendicular to the occlusal plane at the intersection of the anterior border of the ramus and the crista temporalis. Furthermore, the mesial rotation of the third molar was measured and the relation of the bony structures surrounding the teeth were described. Comparison of the CT results with the quotients of the P1 showed that, for those wisdom teeth molars with an available space above 50% to under 100%, any of the 3 CT gradings was found. Assessing the projection of the ramus over the third molar as seen in the P1, 60% of the P1- and CT-results corresponded. The relation between the line L and the third molar showed coincidence in 76% of all cases. These results and the mesial rotation of the wisdom teeth as well as their different relation to the bony environment are possibly important factors concerning their eruption prognosis. The three-dimensional CT-scan gives new possibilities for further investigations of third-molar problems.