饰瓷与基底瓷双层结构全瓷冠残余应力的三维有限元分析

目的探讨全瓷冠高温烧结后冷却过程中,冠内不同部位以及结合界面处残余应力的分布及影响因素。方法三维光学面扫描仪对全瓷修复体基底冠与最终牙冠表面分别进行扫描,获取冠内外点云数据;Geomagic Studio8与UG NX5将扫描后的壳体模型转成三维实体模型;运用有限元分析软件ABAQUS6.7热位移偶合单元对模型进行网格划分,施加温度载荷,模拟全瓷冠高温烧结后冷却过程,分析全瓷冠残余应力分布,并以修饰瓷与基底瓷热膨胀系数相同模型进行对比。结果建立起饰瓷与基底瓷双层结构的全瓷冠三维有限元模型。残余应力在全瓷冠颈缘处修饰-基底瓷结合界面分布最大,在修饰瓷较厚部位残余应力分布较小。随着烧结温度的降低,残余应力逐渐增大。结论运用三维面扫描建立的双层全瓷冠三维有限元模型精确,方法简便;全瓷冠残余应力分布较高部位与临床修复体的易破坏部位一致,提示,在进行全瓷冠修复时要注意基底瓷与修饰瓷热膨胀系数的匹配并且要保证冠边缘保持足够的瓷层厚度。

Finite element analysis of residual stress in a bilayered all-ceramic crown

Objective To investigate the residual stress distribution of a bilayered all-ceramic crown during the cooling process using the finite element method.Methods The 3D point picture of a bilayered all-ceramic crown was obtained through three dimentional sensing system(3DSS).Geomagic Studio8 and UG NX5 were employed to transform the 3D point picture of a bilayered all-ceramic crown into a 3D solid model.The residual stress of the model was analyzed.The results were compared when the coefficient values of the veneer and core were the same.Results A 3D finite element model of bilayered dental ceramic crown was established.The maximum residual stress was found at the interface between the core and veneer on the margin of all-ceramic crown.The residual stress was minimum where the veneer ceramic was thickest.The residual stress also increased with the cooling temperature decreasing.Conclusion The method used to build a bilayered ceramic crown is convenient and accurate.The position of maximum residual stress in ceramic crown is the same as that in all-ceramic crown which is easily broken in clinic.Thermal match between core and veneer ceramic and the thickness of the margin of all-ceramic crown should also be taken into account in all-ceramic crown repair.