Center of resistance of maxillary canines: a 3D computational model for orthodontic applications

Introduction The center of resistance (CRES) is regarded as the fundamental reference point for predictable tooth movement. Only a handful of studies have evaluated the CRES of a maxillary canine; however, most had a low sample size, used idealized models, or involved 2D analysis. The objectives of this study were to determine the 3D location of the CRES of maxillary canines, evaluate its variability, and investigate the effects of applying orthodontic load from two directions on the location of the CRES. Methods Cone-beam computed tomography (CBCT) scans of 50 maxillary molars from 25 patients (mean age, 20.8 ± 8.7 years) were used. CBCT images were manipulated to extract 3D biological structures via segmentation. The segmented structures were cleaned and converted into virtual mesh models made of tetrahedral triangles having a maximum edge length of 1 mm. The block, which included the canines and periodontal ligament, consisted of a mean of 4863 ± 1544 nodes and 23 501 ± 8512 tetrahedral elements. Specialized software was used to preprocess the models to create an assembly and assign material properties, interaction conditions, boundary conditions, and load applications. Specific loads were applied, and custom-designed algorithms were used to analyze the stress and strain to locate the CRES. The CRES was measured in relation to the geometric center (R point) of the buccal surface of the canine. Results The average location of the CRES for the maxillary canine was 3.91 ± 1.33 mm palatal, 6.52 ± 1.24 mm distal, and 8.37 ± 2.39 mm gingival relative to R. None of the canines showed a convergence of the CRES at a single point, but the difference was not significant (P > .01). In the anteroposterior and the vertical planes, the CRES showed significant association with root divergence (P < .01). Conclusion The canine CRES was found distal, apical, and palatal to the R point. It was located at 61.5% of the total tooth length or 17.2 mm measured from the cusp tip. Anatomic variation and orientation have a significant impact on the 3D localization of the CRES.