固定桥不同桥体龈端形态修复下颌第一磨牙的三维有限元分析

目的　应用三维有限元分析法探讨不同桥体龈端形态对固定桥基牙及牙周膜应力分布的影响。方法　利用健康成人牙列的锥形束CT（CBCT）原始数据，通过三维建模软件建立下颌第一磨牙缺失，第二前磨牙与第二磨牙为基牙的双端固定桥，并模拟三种不同桥体龈端形态，即改良鞍式、改良盖嵴式、船底式。利用Ansys 17.0对已建立的三种不同龈端形态的固定桥有限元模型加载垂直向载荷，分析固定桥基牙牙本质、牙周膜的应力分布情况。结果　①三种龈端形态的固定桥在相同载荷条件下第二前磨牙牙周膜应力均较第二磨牙应力值大；②桥体龈端形态均不会影响单个基牙应力分布的规律；但与其他两种形态的修复体相比，船底式龈端形态的单根基牙综合应力值更小，且双根牙综合应力值更大；③固定桥受垂直载荷时三组桥体基牙牙周膜综合应力分布大小依次为：改良鞍式＜改良盖嵴式＜船底式，但三者应力均未超出基牙牙周储备力，只是随着桥体龈端面积减小，基牙动用的牙周储备力增加。结论　①磨牙是比较理想的基牙，在修复时，应首先考虑的是前磨牙的牙周支持力是否充足；②船底式固定桥修复后更有利于保护单根基牙，改善固定桥应力分布；③三种龈端修复形态下基牙牙周支持组织都能承担日常咬合力，对基牙牙周膜健康无影响。

Three-dimensional finite element analysis of the three gingival types of fixed bridge with the lack of the first mandibular molars

Objective To investigate the effect of different gingival types of fixed bridge on the stress distribution of the abutment and periodontium via the method of three-dimensional finite element analysis.Methods A fixed bridge with the mandibular second premolar and the second molar acting as the abutment to restore the missing first molar was established using three-dimensional modeling software based on original cone beam computed tomography(CBCT)data of healthy adult dentition.Three different types of bridge gingival ends were simulated,namely modified saddle type,modified crest type and bottom type.After vertical loadings were exerted on three kinds of finite element models respectively,the stress distributions of dentin and periodontal membrane of the fixed bridge abutment were analyzed using ANSYS 17.0 software.Results(1)The second premolar teeth always suffered higher stress compared with the first molar teeth under the same loading condition.(2)The stress distribution of a single teeth showed no significant difference among three different gingival types of fixed bridge,while the bottom type of prosthesis showed smaller stress in the second premolar teeth and bigger stress in the first molar teeth.(3)The stress distribution of the periodontal membrane of the three groups of bridge abutment teeth was as follows:modified saddle type