Objectives

This study aimed to investigate the collective influence of material properties and design parameters on the fracture behavior of monolithic dental crowns.

Methods

Three-dimensional (3D) models (N = 90) with different combinations of design parameters (thickness, cusp angle and occlusal notch geometry) and material type (lithium disilicate, feldspar ceramic, zirconia, hybrid resin ceramic and hybrid polymer-infiltrated ceramic) were developed for the failure analysis using extended finite element method (XFEM) to identify the stress distribution, crack initiation load, fracture surface area and fracture pattern. Analytical formulation, in vitro fracture tests and fractographic analysis of dedicated models were also performed to validate the findings of the XFEM simulation.

Results

For all material types considered, crowns with a sharp occlusal notch design had a significantly lower fracture resistance against occlusal loading. In most of the models, greater crown thickness and cusp angle resulted in a higher crack initiation load. However, the effect of cusp angle was dominant when the angle was in the low range of 50° for which increasing thickness did not enhance the crack initiation load.

Significance

Comparing the critical load of crack initiation for different models with the maximum biting force revealed that for the studied monolithic materials excluding zirconia, a design with a rounded occlusal notch, 70° cusp angle and medium thickness (1.5 mm occlusal) is an optimum combination of design parameters in terms of tooth conservation and fracture resistance. Zirconia crowns exhibited sufficient strength for a more conservative design with less thickness (1.05 mm occlusal) and sharper cusp angle (60°).

中文翻译：

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整体式牙冠断裂分析：材料性能，尖角和牙冠厚度的影响。

目标

这项研究旨在调查材料特性和设计参数对整体式牙冠断裂行为的共同影响。

方法

 具有设计参数（厚度，尖角和咬合槽口几何形状）和材料类型（二硅酸锂，长石陶瓷，氧化锆，混合树脂陶瓷和混合聚合物渗透陶瓷）的不同组合的三维（3D）模型（N = 90）使用扩展有限元方法（XFEM）进行故障分析，以识别应力分布，裂纹萌生载荷，断裂表面积和断裂模式。还进行了分析配方，体外断裂试验和专用模型的形貌分析，以验证XFEM模拟的结果。

结果

对于所有考虑到的材料类型，具有清晰咬合缺口设计的牙冠对咬合负荷的抗断裂性明显较低。在大多数模型中，较大的胎冠厚度和尖角会导致较高的裂纹萌生载荷。但是，当夹角在50°的较低范围内时，尖角的影响最为明显，对于该范围而言，增加厚度不会增加裂纹萌生载荷。

意义

将不同型号的裂纹萌生的临界载荷与最大咬合力进行比较后发现，对于除氧化锆外的整体研究材料，具有圆形咬合槽，70°尖角和中等厚度（1.5 mm咬合）的设计是最佳的组合。牙齿保护和抗断裂性方面的设计参数。氧化锆冠展现出足够的强度，可用于更保守的设计，厚度更小（咬合1.05 mm），尖角更尖（60°）。