Abstract: Objective　To investigate the stress distribution of restoration，residual dental tissue，enamel，dentin，adhesive layer of mandibular first molars with different bottom thickness by using lithium disilicate ceramic onlay. Methods　To collect one tooth of mandibular first molars in vitro with all values are in the normal range. To establish 3 D finite element model of this mandibular first molar meiso-occlusal cavity with different bottom thickness（h）by CBCT scanning technology，Mimics19.0，Hypermesh and ANSYS Workbench15.0 reverse engineering software. With the h=0 mm，1 mm，3 mm，5 mm as a variable，respectively for h0，h1，h3，h5. The stress distribution of each part was analyzed with vertical loading of 300 N or oblique loading of 180 N. Results　（1）Under vertical loading，comparing the equivalent stress. Restoration：h5 > h3 > h1 > h0，residual dental tissue：h5 > h3 > h0 > h1，enamel：h3 > h5 > h1 > h0，dentin：h0 > h1 > h3 > h5，adhesive：h5 > h0 > h3 > h1. During oblique loadin，restoration：h5 > h3 > h1 > h0，residual dental tissue：h1 > h3 > h5 > h0，enamel：h3 > h5 > h1 > h0，dentin：h0 > h1 > h3 > h5，adhesive：h5 > h3 > h0 > h1.（2）At the same bottom thickness，the equivalent stress range of each part is different；and at the different thickness，the range of the same part is alike. Conclusion　The bottom thickness is an important factor of affecting the stress distribution in the restoration and each part of the tooth. When using lithium disilicate ceramic material as the onlay material to restore the mandibular first molar，bottom thickness material with 1 mm maybe the best. It is conducive to remain the stability of the restoration and each part of the tooth，but it should be pay attention to adjust the cuspal inclination in order to reduce lateral force.

Key words: ceramic onlay, mandibular first molar, finite element analysis, bottom thickness

摘要： 目的　探讨应用二矽酸锂陶瓷高嵌体修复不同垫底厚度的下颌第一磨牙修复体、剩余牙体组织、牙釉质、牙本质、粘接剂的等效应力大小及分布情况。方法　收集一颗完整的离体下颌第一磨牙，通过锥形束CT（CBCT）扫描技术，Mimics19.0、Hypermesh、ANSYS Workbench15.0等逆向工程软件，建立下颌第一磨牙近中面不同垫底厚度的三维有限元模型，以垫底厚度（h）0 mm、1 mm、3 mm、5 mm为变量，分别记为h0、h1、h3、h5，观察静态垂直向加载300 N或斜向加载180 N时修复体、剩余牙体组织、牙釉质、牙本质、粘接剂的等效应力大小及分布情况。结果　（1）垂直向加载时各结构不同垫底厚度等效应力大小比较，修复体：h5 > h3 > h1 > h0，剩余牙体组织：h5 > h3 > h0 > h1，牙釉质：h3 > h5 > h1 > h0，牙本质：h0 > h1 > h3 > h5，粘接剂：h5 > h0 > h3 > h1；斜向加载时各结构不同垫底厚度等效应力大小比较，修复体：h5 > h3 > h1 > h0，剩余牙体组织：h1 > h3 > h5 > h0，牙釉质：h3 > h5 > h1 > h0，牙本质：h0 > h1 > h3 > h5，粘接剂：h5 > h3 > h0 > h1。（2）同一垫底厚度时，各部结构等效应力分布范围不同；不同垫底厚度时，同一结构等效应力分布基本相同。结论　垫底厚度是影响修复体及牙体各结构等效应力大小及分布的重要因素；根据等效应力的大小和分布，当采用二矽酸锂陶瓷材料作为高嵌体修复下颌第一磨牙时，1 mm的垫底厚度有利于修复体及牙体各结构稳定，但需注意调牙合时应减小侧向力。

关键词: 陶瓷高嵌体, 下颌第一磨牙, 有限元分析, 垫底厚度