下颌第一磨牙不同桩核位置数目金合金桩核修复后基牙应力的三维有限元分析

Three-dimensional finite element analysis on the stress of mandibular first molar restored with different locations and numbers of gold alloy posts and cores

背景:磨牙桩核的设计受多因素影响,既要考虑桩数目对固位力的影响,也要兼顾不同数目桩对牙本质应力大小和分布的影响。目的:应用三维有限元分析下颌第一磨牙近中颊壁缺损金合金桩核全瓷冠修复时,桩数目和位置对基牙应力的影响。方法:用锥形束CT数据建立下颌第一磨牙近中颊壁缺损的三维有限元模型,设计7种桩核修复模式:A组在近中颊根放置单个桩,B组在近中舌根放置单个桩,C组在远中根放置单个桩,D组在近中颊和远中根放置2个桩,E组在近中颊和近中舌放置2个桩,F组在近中舌和远中根放置2个桩,G组在近中颊、近中舌和远中根放置各放1个桩,模拟金合金桩核全瓷冠修复,分别在最大载荷(600 N)、垂直载荷(225 N)、斜向载荷(225 N)和水平载荷(225 N)下检测基牙的Von Mises应力分布及最大值。结果与结论:(1)各模型Von Mises应力分布:金合金桩核全瓷冠修复下颌第一磨牙近中颊壁缺损时,随着桩数目和位置的变化,剩余牙本质上Von Mises应力的峰值呈现出不规律变化,应力分布基本相似,主要分布于桩核末端对应的牙本质、远中牙颈部及根分叉区域;(2)不同桩核数目、位置及载荷下的基牙Von Mises应力最大值:当放置单个桩时,在垂直载荷、斜向载荷和水平载荷作用下,远中根内放置桩较近中颊根和近中舌根放置桩,牙本质最大Von Mises值小;随着桩的数目和位置变化,剩余牙本质上Von Mises应力峰值呈现出不规律变化。在相同修复方式下,随着载荷侧向力的增加,基牙Von Mises应力最大值逐渐增加;在近中颊根和近中舌根放置桩时,水平载荷下的基牙Von Mises应力最大值最大;(3)结果表明:金合金桩核全瓷冠修复下颌第一磨牙近中颊壁缺损时,桩核数目和位置对牙本质应力峰值和分布均有影响。

BACKGROUND： The design of post and core of the molar is affected by various factors, including the effect of the number of posts on the retention force and the effect of the number of posts on the dentin stress and distribution. OBJECTIVE： To make a mechanical analysis on the three-dimensional finite element models of the mandibular first molar defect restored with different numbers and locations of gold alloy posts, cores and all-ceramic crown. METHODS： Cone-beam CT based three-dimensional finite element models of post and core restored first mandibular molars were established, with seven different post designs. According to the numbers and location of gold alloy post inserted into root canal, a single post was placed at the mesial buccal root in group A, a single post at the mesial tongue root in group B, a single post at the distal root in group C, two posts at the mesial buccal root and the distal root in group D, two posts at the mesial buccal root and mesial tongue root in group E, two posts at the mesial tongue root and the distal root in group F, one post respectively at the mesial buccal root, mesial tongue root and distal root in group G. The von Mises criterion was applied for comparing the maximum von Mises stress value of dentin and stress concentration areas in the seven models which restored with golden alloy posts and cores with all-ceramic crown under the maximum （600 N）, vertical （225 N）, inclined （225 N） and horizontal （225 N） loads. RESULTS AND CONCLUSION： Under vertical, inclined and horizontal direct loads, the maximum stresses on the remaining dentin in group C were significantly lowest, compared with the groups A and B. The maximum stresses on the remaining dentin changed irregularly with the variation of the numbers and location of posts, when the mandibular first molar defect was restored with all-ceramic crown with gold alloy posts and cores. Under the horizontal load, the maximum Von Mises stress value of the dentin increased remarkably. Under the horizontal load, the maximum stresses on the remaining dentin in group E were the highest. To conclude, the numbers and location of posts and cores have influence on magnitude and distribution of stress, when the mandibular first molar defect is restored with all-ceramic crown with gold alloy post and core.