桩核冠修复后牙多壁缺损三维有限元应力分析

目的:应用三维有限元分析不同数量、不同位置纤维桩核冠修复下颌第一磨牙近远中颊牙合面缺损MDBO(三壁缺损)时牙本质的应力。方法:建立右下第一磨牙三维有限元模型,模拟三壁缺损,根据根管打入纤维桩的不同数目和不同部位分为4组,A组近舌、远中根管各打入纤维桩一根;B组近颊、远中根管各打入纤维桩一根;C组近颊、近舌、远中根管各打入纤维桩一根;D组根管内无纤维桩植入。4组均采用树脂核及钴铬合金烤瓷全冠修复,测试垂直牙合力或45°牙合力加载下Von mises应力和最大拉应力的峰值变化。结果:D组在垂直牙合力或45°牙合力加载下,Von mises应力、最大拉应力的应力峰值均高于A^C组,差异有统计学意义(P<0.05);AC组,差异有统计学意义(P<0.05);A^C组间无差异。4组45°方向加载时牙根桩核应力均大于垂直方向,二者具有显著性差异(P<0.01)。应力图显示牙颈部应力稍高,其他区域的应力值较小却分布较均匀,在根管壁上呈现低应力的分布状态。结论:桩核数目的变化与各组之间剩余牙本质上Von mises应力、最大拉应力的应力峰值变化不大,在桩核固位强度足够的前提下,应尽可能多保存根管外健康的牙体组织,以减少牙根管壁的应力;同时应尽量减少侧向力,以免引起根管壁与桩核较大应力集中,从而降低牙折风险,提高修复体使用寿命。

Stress Analysis in Restoring Multi-wall Defective Distomolar by Using Post-core Crown under Three-dimensional Finite Element Model

Objective To apply the three-dimensional finite element model to analyze the stress of dentine during restoring distal dentomental surface defects of mandibular first molar by using different numbers and location of post-core crown.Methods The three-dimensional finite element model of mandibular first molar was established to mimic the three wall defects. The tooth samples were divided into four groups according to the numbers and location of fiber post inserted into root canal. Two fiber posts were respectively inserted into mesiolingualcanal and distolingual distal root canal in group A. Two fiber posts were respectively inserted into mesiobuccal and distolingual root canal in group B. Three fiber posts were respectively inserted into mesiobuccal,mesiolingualcanal and distolingual root canal in group C. Fiber post was not inserted into root canal in group D. In all groups resin nuclear and Co-Cr based porcelain-fused-to-metal（ PFM） crown were used to multi-wall defective distomolar. Under pressure loading with the angle of vertical or 45 degrees,the changes of Von mises stress and the maximum tensile stress were tested. Results Under pressure loading with the angle of vertical or 45 degrees,the peak values of Von mises stress and the maximum tensile stress in group D were significantly highest,compared with the other three groups（ P〈 0. 05）. The stress distribution figure showed that the stress of tooth neck was higher,the stress values of other locations were lower and well-distributed,the wall of root canal showed lower stress distribution. Conclusion The number of post-core was not related with the peak values of dentinal Von mises stress and the maximum tensile stress.The sufficient strength of post-core retention is a prerequisite in reducing the stress of root canal wall by retaining much more health tooth tissues outside root canal. Meanwhile,side stress should be reduced in order to avoid the intensive stress of root canal wall and post-core,decrease the risk of tooth fracture and extend its l