Comparative effects of temporary anchorage devices combined with various auxiliary attachments on maxillary molar mesialization with clear aligners: a finite element analysis

This study aimed to investigate the biomechanics of maxillary dentition, specifically displacement patterns, midline deviation, and stress distribution of the first molar and anchorage teeth during first molar mesialization using clear aligners (CA) assisted by temporary anchorage devices (TADs) combined with different auxiliary attachments, including buccal buttons, aligner-based angel buttons and power arms. Finite element models of the CA, micro-implants, maxillary teeth, periodontal ligament (PDL), and alveolar bone were constructed. Four finite element models were simulated: model A (CA alone, control); model B (CA with micro-implants connected to aligner-based angel buttons); model C (CA with micro-implants connected to buccal buttons on the first molar); and model D (CA with micro-implants connected to power arms on the buccal surface of the first molar). The simulations evaluated three-dimensional tooth displacement, midline deviation, tipping angles, and PDL hydrostatic pressure of the maxillary dentition. Mesialization of the first molar using CA alone resulted in mesiolingual tipping and intrusion, while anchorage teeth experienced distobuccal or distolingual tipping and extrusion. Midline deviation tended toward the edentulous side due to reciprocal forces. Auxiliary force systems generally improved the efficiency of molar mesial movement from 44.12% to 52.92% and reduced anchorage tooth displacement compared to the control. Aligner-based angel buttons showed the most effective anchorage stability and minimal midline deviation (0.0137 mm). Buccal buttons produced the largest mesial movement of the first molar, with pronounced tipping (0.714°) and uneven PDL stress. Power arms showed near-bodily movement of the first molar and relatively uniform PDL stress, although anchorage control was less pronounced than that of aligner-based angel buttons. The combined use of micro-implants and auxiliary devices demonstrated distinct effects on the first molar mesialization and anchorage teeth stability. Notably, aligner-based angel buttons provided the most effective anchorage control and the least midline deviation, while power arms resulted in more bodily movement of the first molar.