Finite element analysis of the first molar relationships after orthodontic treatment utilizing single-arch extraction of the upper first bicuspids

Abstract

In order to evaluate the validity of Class II occlusal condition of the first molars after orthodontic treatment utilizing single-arch extraction of the upper first bicuspids, computer simulated biomechamcal analysis was carried out. Four sets of setup models were produced. The setup models represented two occlusal conditions (Simple Class II : The Class II occlusal condition with the upper first molar displaced parallel in the mesial direction from a Class I occlusal condition and Modified Class II : The Class II occlusal condition in which mesial rotation and distal angulation were applied to the upper first molar), and two types of upper first molars which differed in terms of the developments of the distal cusps (Type l: well developed and Type 3: poorly developed) . Next, the surface shapes of the setup models were recorded, and the models of the teeth and the bolus (a small mass of food) were produced for the computer simulation. A finite element analysis was applied to the models and the von Mises' stress that arose inside the bolus model was calculated as an index of destruction efficiency of the bolus.
The results were as follows:
1. For the Type 1 upper first molars no remarkable change in the von Mises' stress was recognized between Simple Class II occlusal condition and Modified Class II occlusal condition.
2 . For the Type 3 upper first molars there was a significant change in the von Mises' stress between Simple Class II occlusal condition and Modified Class II occlusal condition.