Xiuping Wu, Yanning Ma, Nan Zhang, Bin Zhao, Wei Wang, Yuxun Cheng, Song Li
Clear aligner treatment is considered to be helpful for periodontitis orthodontics because these aligners are easy to wear and take off. However, studies have shown that the instantaneous force associated with such aligners may affect periodontal tissues. The goal of this study was to identify the optimal orthodontic displacement of clear aligners concerning torque movement using a Three-Dimensional (3D) finite element. We acquired Cone Beam Computed Tomography (CBCT) data from a patient without diabetes and other systemic diseases and who received invisible orthodontics. Based on the different degrees of alveolar bone absorption (1/3 and 1/2 of the root length were reduced horizontally from the alveolar crest along the Z-axis to form alveolar bone models with different degrees of absorption (M1, M2, and M3)), 3D-FEMs of the mandible were established using MIMICS 10.0 and ABAQUS 6.5 software. The 3D stress distribution diagrams and stress values for the teeth (lower incisor, central incisor, lower canine) under three different periodontal conditions (M1, M2, and M3) were then identified by ABAQUS 6.5. The stress values for the root and periodontal ligament increased when the periodontal condition was worse and increased as the level of displacement increased. For patients in which the alveolar bone exhibited 1/3 resorption, we found that when the displacement was 0.18 mm, the stress values of the roots of the anterior teeth (0.591 MPa2.406 MPa) were similar to those of the control group. The stress values of the anterior teeth of the PDL (0.048 MPa-0.216 MPa) were the same as the control group when the displacement was 0.15 mm. For patients in which the alveolar bone exhibited 1/2 resorption, the stress values of the roots of the anterior teeth (0.644-3.969 MPa) were similar to those of the control group; the PDL’s stress values at 0.10 mm (0.056-0.461 MPa) were similar. This experiment showed that when the current tooth is subjected to an additional torque of 5 degrees during lip tilt movement, a clear aligner should be used to reduce the displacement, to avoid greater stress concentration on the root and periodontal ligament. The optimal displacements of M2 and M3 periodontal patients were 0.15 mm and 0.10 mm, respectively.