Biomechanical analysis of the effect of Class II traction configurations and aligner overtreatment on molar distalization: a finite-element study

Objective: This study aimed to evaluate the biomechanical effects of aligner overtreatment on molar distalization using clear aligners.

Methods: Various models were created and integrated into finite-element software. Six distinct study models were devised for analysis. The first three models examined second molar distalization with different configurations of attachments, i.e. no attachment, horizontal or vertical attachment on the second molar. For the fourth and fifth models, Class II elastic traction, either implemented via a precision cut or button on canines, was applied. Lastly, aligner overtreatment with varying degrees of root distal tipping (0°, 2°, 4°, 6°, 8°, 10°, and 12°) for the second molar was designed in the last study model.

Results: Distalization of the second molar produced buccal tipping, distal tipping and intrusion of the second molar, and labial proclination and intrusion of the central incisor. These displacement tendencies were enhanced by adding attachments on the second molar, especially the vertical attachment. Class II elastic tractions enhanced molar distalization and diminish anchorage loss, with the precision-cut configuration being biomechanically superior to the button design. Aligner overtreatment produced bodily molar distalization and mitigated adverse biomechanical effects on anchorage teeth.

Limitations: The study's limitations include the use of finite-element models, which may not fully represent real clinical scenarios, and the lack of consideration for individual patient variability.

Conclusions: We suggest that Class II elastic traction via the precision-cut configuration and the design of vertical attachment on the second molar be applied for molar distalization. Appropriate aligner overtreatment helps achieve bodily molar distalization and minimizes adverse biomechanical effects on anchorage teeth.