The topography of displaced canines: a 3D-CT study

This study investigated the development of a three-dimensional (3D) coordinate system for radiologic volumetric data, allowing the analysis of the tooth axis of displaced teeth in relation to the occlusal, frontal, and sagittal reference planes.

The data basis consisted of multislice computed tomography (MSCT) data of 37 patients with displaced upper canines. A total of 20 patients displayed unilateral displacement and 17 patients bilateral displacement (n = 54). The non-displaced canines of the opposite side served as the reference group (n = 20), together with MSCT data of 6 patients with non-displaced canines (n = 12). Three reference planes were constructed in the VoXim®5.6 program using landmarks (apex point and tip of the canine, incision point of the lower jaw, mesiobuccal tip of the lower left and right first molar, A-point). The tooth axis of the canines was analyzed in relation to these planes.

The angle to the frontal plane was only slightly smaller in non-displaced canines (mean: 17.53°) than in palatally displaced canines (mean: 19.62°), which however exhibited a considerably greater range (0.40-38.00°). In contrast, the mean angle in buccally displaced canines was 32.79°. Both the differences between the reference group and buccally displaced canines and those between the palatally and buccally displaced canines were statistically significant. The angles for buccal (55.16°) and palatal (56.63°) displacement relative to the occlusal plane were significantly smaller than for the non-displaced teeth (70.95°). However, the range of palatal displacement was high (27.3-80.6°). The inclination towards the sagittal plane was slight for non-displaced canines (mean 6.07°) and for buccally displaced canines (mean 8.25°). The mean angle of palatally displaced canines was significantly larger (23.28°) than that in the other groups, with a much greater range (6.70-50.80°).

The 3D coordinate system developed in this study allows the exact measurement of tooth position relative to three spatial planes, thus, enabling tooth position to be objectively determined.