The effectiveness of the attachment position in rotated premolar in clear aligner treatment: a finite element study

The purpose of the study was to evaluate the impact of different placements of vertical rectangular and bevelled vertical rectangular attachments on the correction of rotated premolars with clear aligners using finite element analysis. A three-dimensional finite element model was constructed that included mandibular teeth, periodontal ligament structures and attachments. Rotational correction without attachments were compared to rotational control with two different attachments. Seven different scenarios were created with these attachments positioned on the buccal, lingual and both buccal and lingual surfaces. For all scenarios, 1.2o of aligner activation was applied. The amount of tooth displacement, stress distributions in the periodontal ligament and clear aligner deformation were analyzed. It was observed that the models with attachments demonstrated superior efficacy in rotation correction compared to those without attachments. The tooth demonstrated a clockwise movement in all models. While the highest Pmax (0.1150 MPa), Pmin (-0.1299 MPa) and Von Mises values in the periodontal ligament (0.05279 MPa) were measured in Model 7, the lowest Pmax (0.02461 MPa), Pmin (-0.02992 MPa) and Von Mises (0.01097 MPa) values were measured in Model 1. Among all attachment configurations, the bevelled vertical rectangular attachment positioned both buccally and lingually exhibited the highest levels of displacement (35 μm), stress on the periodontal ligament (0.05279 MPa), and deformation of the clear aligner (88.97 μm). The utilisation of an attachment for the purpose of rotation correction was found to be more effective. The results obtained with the two different attachment types were found to be similar. The addition of a bevel to the attachment and its positioning buccally and lingually resulted in an increase in the amount of movement in the tooth, the deformation of the clear aligner, and the stress experienced by the periodontal ligament.