Biomechanical effects of clear aligners with different distal coverage designs combined with Class II elastic traction for maxillary first molar distalization: a finite element study.

Background: The sequential distalization of teeth may affect the final efficacy of molar distalization in clear aligner treatment (CAT), necessitating additional anchorage protection for distalized posterior teeth. This study aimed to examine the anchorage protection effects of a distal uncoverage clear aligner (DUCA) and Class II elastic traction on the distalized second molar during maxillary first molar distalization.

Materials and methods: Finite element models of maxillary first molar distalization in CAT were constructed. Two different designs of CAs-a distal coverage aligner (DCA) and a DUCA-were utilized for maxillary first molar distalization after the second molar had been distalized by 2 mm. The force value of Class II elastic traction was set to 0, 1, 2, and 3 N. The displacement of the maxillary teeth and CAs was recorded.

Results: Significant biomechanical differences were observed between DCA and DUCA. The initial closure of the space between the first and second molars in the DUCA group was mostly due to the first molar distalization. In comparison to DCA, DUCA exhibited less mesial displacement of the second molar and greater anterior anchorage loss. The anchorage loss reduction of the canines caused by Class II traction was the most pronounced, whereas the impact on the second molar was minimal.

Conclusion: During first molar distalization in CAT, the anchorage protection effect of Class II elastic traction on the distalized second molar was limited. The utilization of a DUCA can effectively mitigate anchorage loss of second molar. Simultaneously, it is crucial to apply a greater Class II traction force to protect the anterior anchorage.