Three Dimensional Simulation Of Gingival Soft Tissue Deformation

Virtual surgery simulation system is an important application of virtual reality technology in medicine.It is of great significance for doctors to practice before surgery and to plan surgery.Virtual surgery uses computer to construct virtual surgery scene and human-computer interaction to realize the operation process.Virtual orthodontic system is a typical application of virtual surgery simulation system.The deformation simulation and modeling of gingival soft tissue is an important part of virtual orthodontic system.Therefore,this paper focuses on the deformation simulation of gingival soft tissue in virtual orthodontic system,and carries out relevant research.The main research contents and innovations are as follows:(1)In view of the existing triangle mesh quality measurement methods are mostly based on a single triangle,for the triangle mesh surface fairing quality measurement,only judging from the visual effect,it is difficult to accurately measure through numerical value,this paper designs a smoothness measurement method to measure the fairing quality of the triangle mesh surface.Through experiments,the accuracy of the algorithm is verified,and the result is consistent with the result of human visual evaluation.This measurement method provides a basis for the evaluation of the simulation effect of gingival soft tissue deformation.(2)In order to solve the problem of hyper-elasticity caused by excessive external force when the traditional mass spring model simulates the deformation of gingival soft tissue,an improved mass spring model based on threshold constraint is proposed.Based on the traditional surface model,the optimal threshold value of the deformation spring is set by comparing the deformation effect and the deformation speed.When the deformation spring is shortened or extended beyond the threshold,the spring length is restored to the original length as the initial length of the next single step deformation,so that the face model has a kind of body feature.In the deformation simulation experiment,the improved model is applied to the deformation simulation of gingival soft tissue in virtual orthodontic system.The results show that the deformation speed of the improved model is increased by more than 28%and the sum of smoothness is significantly reduced,which shows that the improved model can solve the problem of super-elasticity,improve the accuracy of deformation simulation,and simulate the defo rmation process of gingival soft tissue more truly.(3)In order to solve the problem of low quality of the area based adaptive subdivision algorithm,an improved adaptive subdivision algorithm based on vertex smoothness judgment is proposed.In this paper,the vertex smoothness is used as the criterion of subdivision.Before subdivision,the smoothness of vertex 1-domain region is calculated on the whole.By comparing the vertex smoothness and the smoothing threshold,the subdivision region is determined and loop subdivision is carried out.The average smoothness index is designed to evaluate the subdivision effect.This method comprehensively considers the influence of the number of mesh vertices after subdivision on the judgment of subdivision mesh quality,so it can reasonably evaluate the performance of subdivision algorithm.In the subdivision experiment,the improved adaptive subdivision algorithm is applied to the triangular mesh subdivision of gingival deformation area.The results show that the average subdivision time of the improved adaptive subdivision algorithm is about 4.12%saved.After subdivision,the triangular mesh is more regular,more evenly distributed,and the surface fairing quality is better.