Effect of Class II elastics on different mandibular arch preparation stabilized with aligners and stainless-steel wires: A FEM study

Finite element models that simulate the effects of class II elastics on the mandibular arch in six different scenarios, using various immobilization methods of the posterior dentition, were studied. Per-element distribution of linear elastic stress-strain and total displacement was computed. Maximum strain on the PDL and maximum stress on alveolar bone increased with posterior tip-back and with the use of archwires vs. aligners. The configuration of the dentition affects the performance of aligners. They perform best on an unlevelled mandibular arch. Applying class II elastics results in vertical side effects that can be modulated by various mandibular stabilization methods. This is likely to be clinically relevant for high-angle patients and may explain the differing effects on the facial profile observed using various treatment modalities. 1-Increasing mandibular molar tip-back generally resulted in less eruption tendencies, with mandibular anchorage preparation resulting in the least amount of calculated vertical displacement. 2-Unexpectedly, with class II forces the use of aligner technology on an unlevelled curve of Spee resulted in improved vertical control when compared to aligner use on a levelled dentition. 3-Generally, using an archwire results in better transmission of stresses to adjacent teeth than the use of aligners. 4-Simulating interarch elastics requires implementing a medial component/orientation of the forces to better emulate clinical situations. 5-A hypothetical configuration: 15(o) tip-back of the mandibular second molar and aligner stabilization displayed the least amount of vertical movement and the most forward horizontal movement of the 2nd molar.