纤维桩修复上颌第一磨牙牙体缺损的三维有限元力学分析

Three-dimensional finite element analysis on fiber-reinforced composite post-restored maxillary first molar with tooth defect

目的·探究纤维桩修复上颌第一磨牙腭面(palatal-occlusal,PO)和远中邻面(distal-occlusal,DO)牙体缺损时适宜的修复策略。方法·建立上颌第一磨牙PO和DO 2种牙体缺损模型,每种缺损类型采用不放纤维桩(no post,NP)、腭根单纤维桩(palatal post,PP)、腭根及远颊根双纤维桩(palatal and distobuccal posts,PDP)、腭根及近颊根双纤维桩(palatal and mesiobuccal posts,PMP)以及三根管纤维桩(palatal,distobuccal and mesiobuccal posts,PDMP)5种不同策略进行全冠修复的有限元模型。若多桩组的纤维桩在树脂核内出现干扰,则将较细的桩于重叠处下方1 mm处水平截断。对各模型分别加载与牙体长轴平行的800 N垂直力和与牙体长轴呈45°角的225 N侧向力。通过有限元分析计算牙体组织和纤维桩内的等效应力及纤维桩-树脂水门汀、树脂水门汀-根管壁界面上的最大切应力。结果·对于牙体外表面的最大等效应力值,垂直载荷下PO缺损的PMP组和DO缺损的PDP组最小(分别为36.17 MPa、36.23 MPa),侧向载荷下PO缺损的PDMP组和DO缺损的PMP组最小(分别为40.47 MPa、42.05 MPa)。在2类牙体缺损中,置入纤维桩后根管内表面颈1/3的应力值普遍下降,中1/3的应力值普遍上升;腭根桩和近颊根桩中的最大等效应力值分别为垂直载荷和侧向载荷下的最高值(分别为60.75~71.29 MPa,45.91~51.82 MPa),相对应的纤维桩-树脂水门汀界面上最大切应力值也为相应载荷下的最高值(分别为11.26~12.93 MPa,12.38~13.03 MPa)。各组在垂直载荷下水门汀-根管壁界面上的最大切应力值相近(9.96~10.58 MPa),而在侧向载荷下PMP组和PDMP组水门汀-根管壁界面上的最大切应力值较高。结论·上颌第一磨牙应根据不同的牙体缺损类型采取不同的纤维桩修复策略:PO缺损宜采用腭根单纤维桩修复;DO缺损宜采用腭根加近颊根双纤维桩修复,同时控制垂直力。

Objective·To explore the appropriate strategy for restoring maxillary first molars with palatal-occlusal(PO)defect or distal-occlusal(DO)defect by using fiber-reinforced composite posts.Methods·Two types of defects in maxillary first molars were established:PO defect and DO defect.For each type,5 finite element models with different restoration strategies were created:no post(NP),palatal post(PP),palatal and distobuccal posts(PDP),palatal and mesiobuccal posts(PMP),and palatal,distobuccal and mesiobuccal posts(PDMP).In the multi-post groups,if 2 posts overlapped in the resin core,the thinner one was horizontally trimmed 1 mm below the intersection point.The models were loaded by a vertical force—an 800 N force parallel to the long axis of the tooth,and a lateral force—a 225 N force directed at 45°to the long axis of the tooth.The following parameters were calculated by using finite element analysis:equivalent stress in the tooth structure and the posts,and maximum shear stress on the post-cement and cement-canal interfaces.Results·Under the vertical loading,the maximal equivalent stress on the external surfaces of the tooth with PO defect was the lowest in the PMP group(36.17 MPa),while it was the lowest in the PDP group with DO defect(36.23 MPa).Under the lateral loading,it was the lowest in the PDMP group with PO defect(40.47 MPa),while it was the lowest in the PMP group with DO defect(42.05 MPa).With either defect,the equivalent stress on the internal surfaces generally decreased at the cervical 1/3 of root canals and increased at the middle 1/3 after post inserting.Palatal canal post and mesiobuccal canal post respectively withstood the highest equivalent stress under vertical loading and lateral loading(60.75‒71.29 MPa and 45.91‒51.82 MPa,respectively),and the maximal shear stresses on these two post-cement interfaces were also the highest under the corresponding loading(11.26‒12.93 MPa and 12.38‒13.03 MPa,respectively).The maximum shear stresses on the cement-canal interfaces were similar among the groups under the vertical loading(9.96‒10.58 MPa),while under the lateral loading they were higher in the PMP group and the PDMP group.Conclusion·The appropriate strategy for fiber-reinforced composite post restoration on maxillary first molars should be determined according to the type of tooth defect.For PO defect,the strategy of one post restoring in palatal canal is recommended;for DO defect,the strategy of two posts restoring in palatal and mesiobuccal canals respectively with approaches to reduce vertical occlusal force is recommended.