Spatially-dense three-dimensional analysis of the midfacial skeletal shape asymmetry in skeletal Class III patients

Introduction This study aimed to analyze midfacial skeletal shape asymmetry in skeletal Class III patients using a three-dimensional spatially-dense method. Methods Sixty skeletal Class III patients' cone-beam computed tomography images were retrospectively enrolled and divided into three groups according to occlusal plane inclination (OPI) and mandibular lateral deviation (MD). A spatially-dense template of the anterior outer surface of the midfacial skeleton was established and validated. Through template registration, a large number of homologous quasi-landmarks of the midfacial skeleton were automatically identified. After robust superimposition of the original and mirror images, the root-mean-square error was calculated as the asymmetry index (AI). Color-coded maps were generated to visually display the location and magnitude of the asymmetry. Results The median overall midfacial skeletal AIs of group 1 (with OPI and MD), group 2 (with MD without OPI), and group 3 (without OPI or MD) were 1.55, 1.27, and 1.19, respectively. The overall AI of group 1 was significantly higher than that of group 2 (P < .05) and group 3 (P < .01). Within group 1, the AI of the alveolar process was significantly higher than that of other regions. Conclusions The three-dimensional spatially-dense method allows quantitative and visual analysis of shape asymmetry of the midfacial skeleton. Skeletal Class III patients with occlusal plane inclination and mandibular lateral deviation exhibit a significantly greater degree of midfacial skeletal asymmetry, with the alveolar process identified as the main asymmetric site of their midfacial skeleton.