Three-dimensional finite element analysis of the uprighting movement of mandibular mesially inclined second molars

Introduction: The mesially inclined mandibular second molar can be supported upright by the microimplant anchorage. This study established the finite element model to analyze the displacement trend and periodontal ligament (PDL) stress distribution of the uprighting mandibular second molar with the microimplant under different conditions. Methods: A 3 -dimensional model of the mandible and dentition was established. The mesial inclination of the mandibular second molar was 30 degrees, 45 degrees, and 60 degrees. Microimplants were implanted between the buccal side of the second premolar and the first molar and in the distal part of the mandibular second molar, respectively. Six groups were set, each loaded with 0.5 N of force. The second molar initial displacement trend and PDL stress distribution were evaluated. Results: The PDL stress of mandibular second molars in all groups was within the physiological limit, and the PDL stress of mandibular second molars in the distal implant groups was lower than that of mandibular second molars in the mesial implant groups. PDL stress concentration in the cervical area. Tooth displacement decreased as the mesial inclination angle of the second molars increased. The sagittal displacement of mesial implant groups was larger, and there was a tendency of mesiobuccal torsion when standing uprighting; the vertical displacement of distal implant groups was larger, and there was a tendency of distal lingual torsion when standing uprighting. Conclusions: Distal microimplant has a better extrusion effect on the mesially inclined second molar, whereas mesial microimplant has a better effect on the distal movement. The optimal orthodontic force for microimplant traction on mesially inclined second molars is 0.5-0.8 N. (Am J Orthod Dentofacial Orthop 2024;165:314-20)