Finite element analysis on pushing the molar backwards using invisible aligner with different migration displacement.

Purpose: This paper examines the biomechanical mechanism behind the effect of the invisible aligner technique on tooth movement processes.

Methods: To compare the effects of different target positions on tooth movement and the periodontal ligament (PDL), two kinds of aligners were designed to provide displacements of 0.2 mm (Model A) and 0.3 mm (Model B). Different displacements of the maxillary second molar were simulated using the finite element (FE) method.

Results: The results of numerical simulations showed that the maximum stress was in the PDL of the distal surface and the palatal surface. The stress of the PDL in Model B was larger than Model A, with the displacement of the second molar 0.027 mm in Model A, by 44.9% lesser than that in Model B.

Conclusions: The aligner that provided a displacement of 0.2 mm was more suitable for pushing the second molar backward in the initial stage. During the tooth movement processes, the displacement of the crown was larger than that of the root and the displacement decreased gradually from the crown to the root. In addition, the displacement and rotation of teeth during orthodontic treatment were measured and analysed.