下颌第一磨牙牙体缺损修复的三维有限元力学分析

目的:对根管治疗的下颌第一恒磨牙髓室壁未破坏与部分破坏的两种最大远中牙合面牙体缺损充填,全冠与桩核全冠修复进行三维有限元应力分析,为临床修复方式的选择提供一定的理论依据。方法:通过三维激光扫描、三维造型设计技术,建立下颌第一恒磨牙髓室壁未破坏和髓室壁部分破坏的最大远中牙合面牙体缺损,银汞合金、复合树脂充填,镍铬合金全冠修复或铸造镍铬合金桩核全冠、金合金桩核全冠修复的三维有限元模型。观察4种载荷下牙本质Mohr应力分布,比较牙本质最大Mohr值。结果:在最大、垂直、斜向载荷下,两类修复牙本质最大Mohr值均明显小于牙本质拉伸极限强度。髓室壁牙体组织部分破坏的模型,在垂直、斜向载荷下,牙本质最大Mohr值为桩核全冠的小于充填全冠的,应力由充填全冠集中于冠边缘、牙颈部分散到根部。在水平载荷下,两类修复牙本质最大Mohr值均有急剧增加,接近或超过牙本质拉伸极限强度。结论:髓室壁牙体组织是否保留对修复后牙体的抗折力及修复方法的选择有重要影响。

A 3-Dimensional finite element mechanical analysis on structure defect restoration of the mandibular first molar

Objective: To make a mechanical analysis on 3-dimensional finite element models of the mandibular first molar with the maximum distal occlusal structure defect involving pulp chamber wall or not,which were restored by filling and crown or post core and crown, and to provide a guideline for planning restoration for such kind of tooth structure defect. Methods: 3-dimensional finite element models of the maximum distal occlusal structure defect involving pulp chamber wall or not were built using advanced 3-dimensional laser scanning and 3-dimensional computer assisted design technique, which adopted the amalgam filling or composite resin filling and then restoration of NiCr metal crown and NiCr alloy post core and crown or Au alloy post core and crown. The Mohr strength theory was applied for comparing the maximum Mohr stress value of dentin and stress concentration areas in two models under different simulating loads. Results: Under the maximum, vertical and inclined loads, the maximum Mohr stress values of dentin of two kinds of restorations were obviously lower than the tensile limit strength of dentin. Under the vertical and inclined loads, the defect involving pulp chamber wall, the maximum Mohr stress values of dentin of post core and crown were lower than that of filling and crown's. Comparing with filling and full crown restoration, the stress concentration area in the models with the post core and crown restoration transfered to parts of root from crown margin, tooth cervix. Under horizontal load, the maximum Mohr stress value of dentin of the two kinds increased remarkably and was close to or greater than that value. Conclusion: Whether or not reserving of pulp chamber wall had an important influence to resistance of teeth after restoration and selecting methods of proper restoration.