The evaluation of the torque control parameters in upper incisors with finite element analysis during posterior expansion in clear aligner treatments

ÖGÜT ÖZUĞUR, E. (2024) The Evaluation of the Torque Control Parameters in Incisors with Finite Element Analysis During Posterior Expansion in Clear Aligner Treatments The aims of this study were first to evaluate the effect of the posterior expansion with clear aligner on both posterior and anterior teeth using Finite Element Method (FEM), and then to compare the effectiveness of the attachments or power ridges to prevent torque loss of the anterior teeth during posterior expansion by determining the stress distribution on the teeth and periodontal ligament, and the amount of displacement of the teeth. The study focused solely on dental expansion, utilising cone-beam computed tomography (CBCT) data from a 19-year-old female with median palatal suture fusion. Bone modelling was conducted using 3D Slicer software, including reverse engineering and 3D computer-aided design (CAD) activities. Solid models compatible with analysis environments were generated, and meshing was optimised using ANSYS Workbench software. The LS-DYNA solver was employed to solve finite element models. The aligner thickness was determined as 0.76 mm. Buccal expansion activation was 0.2 mm with 1.5° buccal root torque. In the first phase of the study, Model 1.1 was attachment free model whereas Model 1.2. included gingival beveled horizontal attachments (GBHA) on the posterior teeth. In the second phase of the study, additional 3 models were compared based on Model 1.2; Model 2.1 with labial and palatal power ridges on the central incisor, Model 2.2 with a labial horizontal attachment on the central incisor and Model 2.3 with a labial GBHA on the central incisor. Model 1.2 showed more parallel movement compared to the Model 1.1 attachment free model during posterior expansion with clear aligner. With Model 1.1, a greater expansion was obtained. In both models, incisors showed retroclination during posterior expansion. In Model 2.1, 2.2 and 2.3, adding attachments and power ridges to central incisor prevented retroclination of the incisors. In all the models, the von Mises stresses were higher at the central and lateral incisors compared to the posterior teeth. On the periodontal ligament, main stresses were found to be distributed on the premolars. As a conclusion, this FEM study demonstrated that the use of attachments on the posterior teeth during expansion with clear aligners is effective to prevent buccal tipping of the molars. Furthermore, adding horizontal attachments or double power ridges on the central incisor avoid retroclination of anterior teeth during expansion with aligners. Keywords: FEM Analysis, Torque Control, Expansion, Clear Aligner Treatment