Influência do posicionamento do Parafuso Expansor Hyrax nos movimentos dentários e no ligamento períodontal: um estudo com elementos finitos

Abstract

The objective of this study was to simulate different vertical and anteroposterior positions of the expander screw of hyrax appliance and assess the displacement of the teeth and the patterns of distribution of forces in the periodontal ligament using the finite element method (FEM). The part of the maxilla with teeth, periodontal ligament, midpalatal suture, and the hyrax appliance were modeled, and 6 distinct FEM were created to simulate different positions of the expansion screw.There were 2 vertical positions at distances of 20 and 15 mm from the occlusal plane. Another 3 positions were anteroposterior, with the center of the screw placed between and equidistant from the mesial face of the first molar and the distal face of the first premolar aligned to the center of the crown of the first molar, and the anterior edge of the screw aligned to the distal face of the first molar.The initial activation of 1mm of the expander screw was simulated in each model. The first premolar (U4) and the first molar (U6) presented the greatest displacement and concentration of stress and compression; the most anterior and occlusal position of the expander screw was the one with the greatest displacement and stress on the teeth. U4 and U6 showed counterclockwise rotation; more expressive in U4.The teeth showed an intrusive displacement of the vestibular face and an extrusive aspect of the palatine face, except for U4 which showed a tendency for vestibular extrusion and lingual intrusion.The dental crowns moved in the vestibular direction and the roots in the lingual direction whereas U4 presented an inverse tendency. Stress concentration occurred on the vestibular face of lingual roots and on the cervical region of lingual faces and compression was located in the cervical region of vestibular roots. The variation of the vertical and anteroposterior positioning of the expander screw interfered in the displacement and also in the distribution and intensity of forces on the teeth. The most anterior and occlusal position of the expander screw produced a more effective transference of mechanical effort to the teeth resulting in bigger displacement.