An in-vitro study under cyclic loading on post-and-cores for endodontically treated teeth without coronal extension

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Root fracture caused by post and cores occurs often in daily practice resulting in extraction of the teeth. In this study a new method of post-and-core restoration was developed using a thin layer of Co-Cr coping between cores and crowns and its effectiveness was examined by the static and cyclic loading tests.In the first research year, fracture strength and pattern of the post-and-cores with and without the Co-Cr coping were examined under the static loading using bovine teeth. As a result, the post-and-core with the Co-Cr coping was useful in the endodontically treated teeth with 0 mm and 1 mm coronal extension.In the second research year, two types of margin design, shoulder and beveled shoulder types, were examined under the cyclic loading. Each specimen immersed in 37℃ of water was added by the load of 300N with 1 Hz of 300,000 cycles. After cyclic loading the static loading was added also until the specimens were broken. As a result, the Co-Cr coping was found to be effective to improve the fracture strength in the beveled shoulder type of margin design, though not effective in the shoulder type. Highly decayed endodontically treated teeth remain in difficulties to artificially restore their crowns and very often indicate short longevity of the crowns. This in vitro study suggests the effectiveness of a thin layer of Co-Cr coping in the severe condition of endodontically treated teeth.