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

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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.