Fracture Strength of Endodontically Treated Teeth Restored with Various Core-Buildup Methods after Cyclic Loading

本课题采用一种新的实验方法，以牛牙为材料，模拟制作上中切牙后，在距牙釉质粘接处0 mm、1 mm、2 mm三个高度处切冠，制作出多颗大小、形状相同的牙齿。分别采用传统铸造桩核（Ag-Pd-Au合金）、复合树脂桩核加预制金属桩（不锈钢）和复合树脂桩核3种方法制作桩核。在RL-1型循环加载机上，以250 N/s的速度加载30万次，检测其断裂强度和断裂模式。结果表明，在0 mm冠向延伸时，只有3种方法的复合树脂桩核在循环载荷作用下其断裂强度显著降低，同时显著低于其他两种方法。在1 mm和2 mm冠状面延伸段中，三种方法的断裂强度几乎相同，不受循环载荷的影响。三种方法的断裂方式也无差异。因此，可以得出结论，1 mm冠状面延伸的牙齿结构是临床上非常重要的，有一个良好的结果。

In this project, a new experimental method to provide a lot of teeth with the same size and shape by bovine teeth was developed and after simulated fabrication of the upper central incisors their crowns were cut down at the three levels of coronal height, 0mm, 1mm and 2mm from cement-enamel junction. Those specimens were built up with three kinds of core buildup methods ; conventional cast post and cores (Ag-Pd-Au alloy), composite resin core with prefabricated metal post (stainless steel) and composite resin post and cores. Then they were crowned, immersed in the water, loaded with 250N at every second until 300, 000 times under cyclic loading machine (RL-1), and examined regarding fracture strength and modes. In addition, the fracture strength and modes without cyclic loading was also measured.As a result, in 0mm coronal extension, fracture strength of composite resin post and cores only among three methods decreased significantly after cyclic loading and at the same time was significantly lower than that of the other two methods. In 1mm and 2mm coronal extensions, fracture strengths of three methods indicated almost the same values and were not influenced by cyclic loading. There were no differences among fracture modes of three methods also. Therefore, it could be concluded that 1mm coronal extension of tooth structure is clinically very important to have a good outcome.