下颌第一磨牙不同位置和数目氧化锆桩核冠修复后的三维有限元应力分析

Three-dimensional finite element stress analysis of mandibular first molars restored different sites and numbers of zirconia post-cores and all ceramic crowns

目的通过建立近中颊壁缺损的下颌第一磨牙有限元模型,模拟氧化锆桩核全瓷冠修复效果,分析不同桩核设计对修复效果的影响。方法提取锥形束CT扫描下颌第一磨牙离体牙的数据,使用Mimics、Geomagic、Ansys软件,建立氧化锆桩核全瓷冠修复近中颊壁缺损的下颌第一磨牙有限元模型,依据放置桩的根管数目和位置不同建立7组模型(A:远中根管;B:近中颊根管;C:近中舌根管;D:远中和近中舌根管;E:近中颊和近中舌根管;F:远中和近中颊根管;G:远中、近中颊和近中舌根管),比较最大载荷(F1)、垂直载荷(F2)、斜向载荷(F3)和水平载荷(F4)4种载荷下7组模型基牙Von Mises应力峰值及分布。结果氧化锆桩核全瓷冠修复下颌第一磨牙近中颊壁缺损时,桩的数目、位置对牙本质Von Mises应力峰值及分布影响显著。G组模型在F1、F2、F3和F4四种载荷下,牙本质最大Von Mises应力分别为41.6498、20.5315、20.4553、40.8043 MPa,均小于其他6种模式;F组模型在F1、F2、F3和F4四种载荷下,牙本质最大Von Mises应力分别为41.8181、20.5414、27.2719、43.6618 MPa,除F3载荷时大于D组和G组模型外,F1、F2和F4载荷时均小于A、B、C、D和E组。结论氧化锆桩核全瓷冠修复下颌第一磨牙近中颊壁缺损时,桩核的数目和位置会对修复效果产生显著影响。推荐在近中颊根管和远中根管均放置桩或3个根管均放置桩,3个根管均放置桩更利于分散牙本质应力。

Objective To establish finite element models of the mandibular first molar with mesiobuccal wall defects than enables simulating the efficacy of repair with zirconia post-core all-ceramic crowns,and to analyze the impact of different post-core designs on the repair efficacy.Methods Data of the mandibular first molar in vitro were extracted from cone beam CT scans.Mimics,Geomagic and Ansys softwares were used to establish the finite element model of the mandibular first molar repair in mesiobuccal defects using zirconia post-cores and all-ceramic crowns.According to the sites and numbers of root canals where the posts were placed,there were seven models were established,namely,model A for post placement in the distal root canal,B for the mesiobuccal root canal,C for the mesiolingual root canal,D for the distal and mesiolingual root canals,E for the mesiobuccal and mesiolingual root canals,F for the distal and mesiobuccal root canals,and G for the distal,mesiobuccal and mesiolingual root canals.These models were compared for the peak value and distribution of Von Mises stresses under 4 types of loading:maximum load(F1),vertical load(F2),oblique load(F3)and horizontal load(F4).Results For mandibular first molar repair in mesiobuccal wall defects using zirconia post-cores and all-ceramic crowns,the number and site of the post had a significant impact on the peak value and distribution of Von Mises stresses upon the dentin.Under the four types of loading(F1,F2,F3 and F4),the maximum Von Mises stresses upon the dentin were 41.6498,20.5315,20.4553,and 40.8043 MPa with model G,respectively,which were smaller than those with the other six models.Under the four types of loading(F1,F2,F3 and F4),the maximum Von Mises stresses upon the dentin were 41.8181,20.5414,27.2719,and 43.6618 MPa with model F,respectively;except for the models D and G under the loading of F3,these peak stresses were smaller than those with models A,B,C,D and E under the loading of F1,F2,and F4.Conclusion For mandibular first molar repair in mesiobuccal wall defects using zirconia post-cores and all-ceramic crowns,the number and site of the post had a significant impact on the peak value and distribution of Von Mises stresses upon the dentin.Recommendably,the post may be placed at the mesiobuccal and the distal root canals,or all of the three root canals.Placement of posts on all of the three root canals are more conducive to dispersing the stress on dentin.