Biomechanical effects of different initial posterior inclinations during extraction space closure with clear aligners: A finite element analysis.

Introduction: This study aimed to evaluate the biomechanical effects of different initial mesiodistal inclinations of posterior teeth during extraction space closure using clear aligner treatment.

Methods: Three different finite element models were developed for first premolar extractions, each representing different initial mesiodistal inclinations of the posterior teeth: model 1 with 15° mesial inclination, model 2 with upright posterior teeth, and model 3 with 10° distal inclination. A total of 12 en-masse retraction aligner models with varying posterior antitipping designs (0°, 1°, 2°, and 3°) were constructed to simulate space closure.

Results: From models 1 to 3: Sagittally, posterior teeth increased mesial crown movement but decreased distal root movement; vertically, posterior teeth reduced crown intrusion but enhanced root intrusion; the posterior rotation center shifted distally and apically. Horizontally, model 3 indicated the greatest mesiolingual rotation of posterior teeth across all models. For anterior teeth, model 1 exhibited the most incisor retraction and lingual tipping, whereas model 3 displayed the least incisor retraction and lingual tipping. In addition, the progressive posterior antitipping design gradually diminished both the mesial tipping of posterior teeth and the lingual tipping of anterior teeth.

Conclusions: Different mesiodistal inclinations of posterior teeth had various biomechanical effects in 3 dimensions during space closure. Careful consideration should be given to the mesiodistal angulation of posterior teeth during extraction space closure with aligners.