Biomechanical analysis of maxillary incisor intrusion with clear aligners under different periodontal conditions: a finite element analysis.

Objectives: To investigate the biomechanical effects and determine the optimal increment for maxillary incisor intrusion using clear aligners across three periodontal conditions via finite element analysis (FEA). Materials and methods: Nine FE models were created in a 3 × 3 design simulating three periodontal states (M1: normal bone level; M2: one-third alveolar bone loss; M3: one-half alveolar bone loss) combined with three intrusion increments (0.10, 0.15, and 0.20 mm). Anterior tooth displacement, root von Mises stress, and periodontal ligament (PDL) maximum compressive stress were analyzed. Results: Tooth displacement and mechanical stresses escalated with greater bone loss and larger increments. Central incisors experienced more pronounced tipping, whereas lateral incisors achieved greater vertical intrusion. Consequently, lateral incisors endured higher stresses; their PDL stress was approximately double that of central incisors. While central incisor intrusion efficiency increased proportionally with increment, lateral incisors in M2 and M3 states demonstrated higher efficiency at the 0.15-mm increment (peaking at 92.0%) than at 0.20 mm. In the M3 state, increasing the increment from 0.10 to 0.20 mm sharply amplified lateral incisor root stress (2.96-8.18 MPa) and PDL stress (0.056-0.114 MPa). Conclusion: Clear aligners produce maxillary incisor intrusion with concurrent tipping. Lateral incisors show higher intrusion efficiency but endure greater mechanical stress than central incisors. Alveolar bone loss exacerbates both tipping tendency and stress. For patients with alveolar bone loss exceeding one-third, the intrusion increment is recommended to be limited to 0.15 mm.