Research On Computer Simulation Methods For Gum Deformation In Virtual Orthodontics Treatment

How to realistically simulate gum deformation is a very complicated and important problem in the development of Virtual Orthodontics Treatment System. The paper concentrated on solving this problem. On the analysis of mass-spring model, a force model for soft tissue surface deformation is established.Firstly, on the basis of analyzing the deformation principle of several common soft tissue physical models, the paper compares their simulation accuracy and speed. Mass-spring model is an experienced model, because of its simplicity,easy operation and stronger fitting for topological structural change. But in our subject, the gum is expressed by a series of triangular facets, which is obtained from STL tooth model by using segmentation method. For conventional mass-spring, to add directly bend spring is difficult. In order to view anti-bending simulation results, a resistance force in the normal direction of the vertex is imposed. The resistance force value is associated with vertex displacement. Then, detailed force analysis for the deformation vertex is emphasized. There are four kinds of force that apply to vertex in the model, which is spring force, gravity, external force and the resistance force in the normal direction of the vertex. For the boundary vertex and other vertex, different force balance equations are expressed to calculate the external force and the displacement values.Finally, we discrete dynamic process of deformation, and simulate the result using a static method. When teeth move a small step, we can know the displacement and calculate the external force of boundary vertex of gum, then calculate the displacement of other vertex by using iterative procedure based on the force model. Iterative will continue till all gum vertexes become still. Based on these computing, we get a frame of gum deformation. Teeth move step by step, and then a series of frames of gum deformation are obtained. The simulation method is presented, and implemented by using Visual C++ and OpenGL. Experiment shows that the method is effective, and the simulation is realistic.