Contact Biomechanics Calculation And Simulation Analysis Of Bracketless Invisible Orthodontic

Compared with brackets,invisible orthodontics without brackets has the advantages of beauty,convenience and hygiene,comfortable wearing,and safety.However,in practical applications,problems such as insufficient expression and overcorrection still plague clinicians.The correction process requires manual intervention based on the doctor’s experience,and it is difficult to achieve the goal of digital precision correction.Insufficient research on underlying biomechanical principles,inaccurate frictional contact models,and the complexity of misfit cases can lead to deviations in digital modeling,numerical calculation,and tooth arrangement planning.In view of this,this paper will start from the biomechanics of frictional contact,and conduct research on the construction of frictional contact model,calculation and simulation of contact stress and strain for invisible orthodontic treatment without brackets:（1）Preparation of digital models of invisible appliances.Tooth-periodontal ligament-invisible appliance combined model is the basis for calculation and simulation of friction contact model.Based on tooth-oral point cloud model,three-dimensional mesh model and surface model of tooth are reconstructed;then based on three-dimensional tooth model,Invisible appliance model（the crown was offset outward by0.75mm）and periodontal ligament model（the root was offset by 0.25mm）are obtained by the method.（2）Construction and numerical solution of a two-dimensional elastic contact model based on microplanes.Local contact part between appliance and tooth is assumed to be a two-dimensional micro-plane.Surface contour shape model of the contact part is simulated by python programming,and contact surface stress and surface displacement are calculated by boundary element method.Deformation parts are square,rectangular and circular,respectively,and the maximum contact stress is 5.0MPa,5.51MPa and 5.85MPa,and the maximum contact displacement is 0.51mm,0.85mm and 1.28mm,respectively.（3）Construction and numerical calculation of a three-dimensional contact mechanics model under assumption of elastic half-space.Based on the elastic half-space fractal theory,asperity contact mechanics model is constructed.Contact load and contact area under elastic,elastoplastic and plastic deformation states is analyzed and calculated.The first elastic-plastic and second elastic-plastic are calculated and analyzed,and contact loads are obtained as 1.05N,2.10N and 2.87N,respectively,and contact areas are respectively 19.6mm~2,40.61mm~2,and 25.53mm~2.（4）Case analysis of comprehensive correction based on finite element method.In this study,One case of central incisor and lateral incisor with torsion and inclination is analyzed by finite element method（FEM）under force and displacement loads.The maximum stress and displacement of the combined moving contact surface are 2.35 MPa and0.38 mm respectively.And theoretical calculation results are in good agreement with simulation results.Relationship between simplified numerical calculation model and complex case simulation model is verified.It provides a reference for further study of biomechanics of invisible correction.