The effect of rotation upon dental structure components following orthodontic fix appliance

BACKGROUND AND AIMS: The purpose of the study is to evaluate through a FEM (Finite Element Method) the effects of the rotation movement upon a complex structure (enamel– pulp -alveolar bone, PDL), for external load. METHOD: The progressive action of a fixed orthodontic device on three teeth: first molar, first and second premolar is modeled and simulated with the components placed on the buccal and palatal surfaces of the tooth. For the reproduction of a situation similar to the real one, the loading of the model was performed through a nodal force applied at a height of the crown, of various amplitudes, F = 1 N; 2, 3 and 4 N. The values of stress are: maximum stress of the whole structure and the shearing effect for the pulp. RESULTS: The characteristics of the material are Young’s E modulus and Poisson’s ratio of the components of the modeled structure. The most stressed elements of the structure are the pulp and the ligament, revealed by von Mises stress. The elements of the structure are mainly stressed in fiber compression in the direction of the moment’s action given by the orthodontic forces and in fiber stretching in the opposite direction. Out of the orthodontic movements: translation, tipping, intrusion-extrusion, rotation is the most dangerous. CONCLUSIONS: The accumulated stress effect in the pulp becomes dangerous. The orthodontic movements given by dental force values higher than 1.5–2N are to be avoided.