磨牙全瓷冠断裂类型的力学实验与三维有限元分析研究

A comparative study of mechanical experiment and three-dimensional finite element analysis on fracture mode of all-ceramic molar crowns

目的通过力学实验和三维有限元研究不同直径半球形压头对全瓷冠断裂强度、断裂类型的影响，以期为临床全瓷冠骀面形态设计提供理论依据。方法分别用直径为4mm、10mm的压头对20个下颌第一磨牙全瓷冠（IPS e．maxpress）试件进行力学实验，观察全瓷冠试件的断裂类型。通过改变三维有限元模型3个受力点的位置及受力大小和方向，模拟直径为4mm、10mm的压头加载于全瓷冠时的应力分布状态，计算主应力的大小及分布。结果三维有限元分析显示，两种压头加载状态下，全瓷冠第一主应力均随载荷的增加而增加；4mm直径压头作用下全瓷冠应力集中在骀面中央窝，而10mm直径压头作用下令瓷冠应力集中于[牙合]面近远中方向窝沟处，呈“一”字形；4mm、10mm直径压头作用下全瓷冠的抗折载荷分别为600～700N和2500—2750N。力学实验显示，4mm、10mm直径压头作用下全瓷冠的主要断裂类型分别为Ⅱ型和Ⅴ型，与三维有限元分析结果一致。结论4mm直径压头多造成全瓷冠中央窝破坏，10mm直径压头多造成全瓷冠和牙体模型严重折裂，提示临床工作中应注意减小全瓷修复体对[牙合]牙的牙尖曲率。

Objective To investigate the influence of indenter diameter on fracture strength and fracture mode of IPS e. max all-ceramic crowns using mechanical experiments and three-dimensional finite element （3-DFE） method, to validate the 3-DFE model using mechanical experiments, and to provide a guideline for occlusal surface design for IPS e. max all-ceramic crowns. Methods A 3-DFE model of an all- ceramic crown on a molar was established using ANSYS10. 0 software. The 3-DFE crown was loaded occlusally at three points to simulate the contact points of a hemispherical indenter loading on the crown. Two indenter diameters （4 mm and 10 mm） were designed by changing loading point, load level and its direction. The stress distribution and the principal stress in the 3-DFE model were calculated. Meanwhile, IPS e. max ceramic crowns were made on a laboratory model and loaded with indenters. The diameters of the indenters were also 4 mm and 10 mm respectively. Fracture mode and fracture-resistance of the crowns were recorded. Results The principal stress increased as load increases for both small and large indenters. Stress concentrated in the central fossa of the 3-DFE crown when loaded with the small indenter. Stress concentration appeared in the middle area of the occlusal surface mesio-distally when 3-DFE crown was loaded with large indenter. The fracture-resistance load was 600 N to 700 N for 4 mm diameter indenter, and 2500 N to 2750 N for 10 mm diameter indenter. Mechanical experiments indicated the same results as those from 3-DFE analysis. Conclusions Both the three-dimensional finite element analysis and the mechanical experiment showed the same results. When loaded with 4 mm diameter indenter, fracture occured in the central fossa of the crown, however, 10 mm diameter indenter usually caused extensive crown damage.