Evaluation of Maxillary First Molar Intrusion Mechanics with Mini-Implant Anchorages Using the Finite Element Method

抄録

This study aimed to evaluate the effect of the maxillary first molar intrusion mechanics with mini-implant anchorages on the Von Mises stress and initial displacement using finite element analysis. A three-dimensional finite model was established using Mimics 17.0, Geomagic Studio 2014, Unigraphics NX 8.5 and Ansys workbench 15 software based on original cone beam computed tomography data. Four loading methods were used. The displacement of the maxillary first molar was calculated along the x-, y- and z-axes, and the von Mises stress distribution was visualized using color-coded scales. Most of the stress was concentrated on the cervical or middle third of the roots of the maxillary first molar and decreased toward the apex in all models. The minimum and more uniform stress distribution appeared around the apical third of the roots. The strongest stress on the periodontal ligament (PDL) and alveolar bone was always around the cervical and root furcation. After intrusion, the maxillary first molar was bodily intruded without tipping in model 1, whereas buccal tipping was observed in models 2 and 4. In model 3, the molar had the tendency of mesial-lingual rotation. The vertical displacements were 95.3%, 79.6%, 95.3% and 79.6% of the total displacements of models 1-4, respectively. All cusps were uniformly intruded in models 1 and 3. Buccal cusps were intruded 50% more than the lingual cusps in model 2. All of the cusps were intruded except for the distal-lingual cusp in model 4. The apical third of the roots suffered the minimum stress and was not prone to evident resorption during intrusion, whereas the maximum stress on PDL was also maintained within the normal physiological range. Four loading methods were available for intrusion. Model 1 was the best, followed by models 2, 3 and 4. The tooth cusp conditions should be considered during molar intrusion.