Effects of maxillary molar distalization using clear aligners during the mixed dentition and early permanent dentition with 3 types of Class II traction: a three-dimensional finite element analysis.

Background: Impacts of the developmental stages of maxillary second molars, methods for distalization of the maxillary first molars, Class II traction application, and different traction modes on three-dimensional molar movements, anchorage tooth displacement, and stress distribution remains poorly understood.

Method: Patients with maxillary second molars in Nolla 4-6 and 7-8 stages were selected for 3D finite element modeling. We analyzed three-dimensional movements and stress distribution in maxillary and mandibular dentitions after unilateral and bilateral distalization of maxillary first molars using clear aligners, with no traction and three types of Class II traction.

Results: In Nolla 4-6 and 7-8 stages, after bilateral molar distalization, maxillary anterior labial inclination, tooth, periodontal membrane and alveolar bone stress were more significant. Movements of maxillary first molars were greater in Nolla 7-8 stages regardless of unilateral or bilateral molar distalization. Either unilateral or bilateral molar distalization, Angel button group provided better anchorage control for central incisors. Precision incision group provided superior anchorage control for lateral incisors and achieved the largest distal movements of maxillary first molars. Lingual button group provided anchorage control for deciduous or permanent canines. Molar distalization modes had no effect on mandibular dentition. Movements and maximum periodontal membrane stress values of mandibular dentition were the smallest in the Angel button group.

Conclusion: When moving molars distally, it's necessary to consider the development of maxillary second molar and evaluate the distalization modes, Class II traction modes and the influence on anchorage teeth, to design personalized treatment plan.