Prediction Of Torque Expression Of Upper Central Incisor Using Different Auxiliaries In Clear Aligners - A FEM Study

BACKGROUND: Torque control of maxillary incisors remains a biomechanical limitation of clear aligner therapy. Auxiliaries such as attachments and power ridges have been proposed to enhance torque expression; however, quantitative evidence comparing their isolated biomechanical effects is limited. This finite element method (FEM) study aimed to predict and compare torque expression of the maxillary central incisor using clear aligners without auxiliaries, with vertical rectangular attachments, and with power ridges. MATERIALS AND METHODOLOGY: A three-dimensional FEM model was constructed from CBCT and intraoral scan data of a patient with normal occlusion. Three models were analyzed: Group I (aligner without attachment), Group II (aligner with vertical rectangular attachment), and Group III (aligner with power ridge). A palatal force of 1.89 N was applied to simulate incisor torque. Displacement patterns along x, y, and z axes and stress distribution within the periodontal ligament (PDL) and alveolar bone were evaluated. RESULTS: Vertical displacement was minimal and clinically insignificant in all groups. Labio-lingual displacement differed markedly: Group III demonstrated the greatest palatal crown and root displacement, indicating superior torque expression, followed by Group II, while Group I showed inadequate root control. Peak PDL stress was highest in the power ridge model (19.62 MPa), moderate with rectangular attachments (14.67 MPa), and lowest without attachments (13.48 MPa). CONCLUSION: Power ridges significantly enhance torque expression of maxillary central incisors and have significant biomechanical advantage and force transmission compared with rectangular attachments or no attachment designs. Vertical rectangular attachments offer limited torque improvement, whereas aligners without auxiliaries are biomechanically insufficient for effective torque control.