Effect of different trimline extension of clear aligners in combination with Class II elastics on the mandibular dentition: a finite element analysis

Abstract

Objective of this study is to evaluate the effect of different trimline extension of aligners and the effect of elastics applied through the slit cutouts and buttons on the mandibular dentition using Class II intermaxillary elastics combined with clear aligner treatment. Three-dimensional (3D) finite element models that simulate the effects of Class II elastics on the mandibular arch in four different scenarios were studied, named, straight and high trimline aligner (HTLA) model with elastic applied through buttons (Model 1), straight and low trimline aligner (LTLA) model with elastic applied through buttons (Model 2), HTLA model with elastic applied through slit cutout (Model 3), LTLA model with elastic applied through slit cutout (Model 4). 3D displacements of the teeth, von Mises stress (VMS) in the periodontal ligament (PDL) were calculated. In all models, the crown of the mandibular anterior teeth moved labially, the root moved lingually, and the mandibular first molars moved mesially. Among all models, labialization of incisors and mesialization of molars was highest in Model 2 and lowest in Model 3. In clear aligner treatment combined with Class II elastics, HTLA was more effective in controlling mandibular incisor proclination and mesial tipping of mandibular molars. The slit cutout models were more effective in controlling mesial tipping of mandibular molars.