Tooth rotational control with varying attachment configurations in clear aligners under compromised periodontal ligament support: a finite element study

With the high prevalence of periodontitis, tooth rotation resulting from periodontal damage can be corrected through orthodontic treatment; however, the biomechanical complexity of tooth movement in compromised periodontal tissues, combined with the inherently low rotation accuracy of clear aligners, present significant challenges to tooth rotational control. This finite element study aimed to explore appropriate attachment configurations for tooth rotation under periodontally compromised conditions. Based on cone beam computed tomography data of a patient, three-dimensional finite element models of the upper dental arch, periodontal ligament (PDL), alveolar bone, aligners, and attachments were created. The right maxillary second premolar(A5) was targeted as the rotated tooth with a 30°clockwise rotation. Simulations were conducted with varying alveolar bone loss levels (0/2/4/6 mm) and attachment configurations (none, vertical/horizontal rectangular, and vertical elliptical). A 1° aligner activation angle was applied, and finite element analysis was performed for 16 conditions to assess tooth displacement, periodontal ligament stress, and aligner condition by Ansys Workbench. All groups achieved counterclockwise rotation of the A5, but exhibited concomitant tipping and intrusion. PDL von Mises stress peaked in the lingual cervical region and exceeded apical values. The vertical ellipsoid attachment produced the greatest rotational displacement and highest cervical periodontal ligament stress. The horizontal rectangular attachment showed a more favorable center of rotation with comparatively large rotational displacement and cervical periodontal ligament stress. The vertical rectangular attachment yielded lower cervical periodontal ligament stress and reduced anchorage loss, but smaller rotational displacement and more pronounced undesired displacement. Increasing alveolar bone loss shifted the center of rotation and increased displacement, accompanied by greater undesired biomechanical effects, anchorage loss, and periodontal ligament stress. The horizontal rectangular attachment showed a condition-specific mechanical trade-off within this framework; therefore, clinical extrapolation should be cautious and supported by patient-specific in vivo validation. Treatment planning for rotational movements should consider periodontal support, with close periodontal monitoring and biomechanically informed attachment selection to reduce unintended movements and periodontal loading.