Three-dimensional Finite Element Biomechanical Analysis Of Mandibular Occlusion And Mandibular Impact After Different Kinds Of Osteotomy

Objective To analyze and study the stress distribution in mandible when chewing and hit by external impacts after different kinds of osteotomy by adopting three-dimensional finite element biomechanics,to explore the changes in mandibular stress caused by biomechanical characteristics of mandible,different kinds of osteotomy and the risks of different postoperative fractures,so as to provide a theoretical basis for preoperative design and intraoperative surgical procedures through mechanical analysis.Methods Normal mandibles of young females were selected in this study,a complete three-dimensional finite element model of mandible was constructed by Mimics and Geomagic software based on CT scan data,and the materials of the 3D model were determined and constrained in Ansys software,to simulate the chewing of mandible when masticatory muscles worked normally,so as to analyze stress distribution in mandible.In addition,based on the occlusal analysis of the 3D model of mandible,curved osteotomy 3D model,splitting osteotomy 3D model and curved osteotomy combined with splitting osteotomy 3D model were simulated in computer,to perform biomechanical study to normal mandible,curved osteotomy 3D model,splitting osteotomy 3D model and curved osteotomy combined with splitting osteotomy 3D model under the same impacts in the same position,to test stress at the same positions of different models,and comparison and analysis were conducted.Results:1.A complete three-dimensional finite element model of mandible was established by Mimics,Geomagic and Ansys software according to CT scan data.2.Curved osteotomy 3D model,splitting osteotomy 3D model and curved osteotomy combined with splitting osteotomy 3D model were established successfully through computer simulation.3.Under the same impacts to normal mandible,the stress is mainly concentrated in the chin,coronoid process,mandibular angle and neck of condyloid process.4.Compared to the preoperative model,mandibular stress of curved osteotomy 3D model did not change significantly,the stress in the neck of condyloid process decreased,but the stress in mandibular ramus increased.The stress in resection margins of mandibular angle and coracoid process changed significantly,up by more than 2 times.5.Compared to the preoperative model,the stress inside and outside of neck of condyloid process as well as the stress in coronoid process of splitting osteotomy 3D model declined,but the stress in the inner plate of remaining mandibular angle was significantly higher than that in normal mandibular angle,and stress in residual inner plate of mandible and upper margin of mandibular ramus was more than 2 times higher than that in the preoperative model.6.Compared to the preoperative model,stress in resection margins of mandibular angle,ramus,coracoid stress of curved osteotomy combined with splitting osteotomy 3D model increased obviously,and stress in coracoid process,outer edge of remaining inner plate increased by nearly 6 times.Conclusion 1.When mandible is chewing,the stress is mainly concentrated in the mandibular condyle,coronoid process and molar region,with the maximum stress located in coracoid process.2.Under the same frontal impact,the fracturing risks of ramus and coracoid stress may increase significantly after curved osteotomy,and the fracturing risk of the neck of condylar process may slightly decrease.The fracturing risks of remaining inner plate of mandibular angle increase obviously after splitting osteotomy.The fracturing risks of top margin of mandibular ramus and coracoid process may significantly increase after curved osteotomy combined with splitting osteotomy,and fracturing risk of top margin of mandibular ramus after curved osteotomy combined with splitting osteotomy is higher than that after curved osteotomy or splitting osteotomy.