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

桩核引起的牙根断裂在日常拔牙中经常发生。本文提出了一种新的桩核修复方法，即在桩核和桩冠之间添加一层薄薄的Co-Cr复盖层，并通过静载和循环加载试验验证了该方法的有效性。在研究的第一年，采用牛齿对柱芯在静载荷作用下的断裂强度和断裂模式进行了研究。结果表明，在冠状延伸0 mm和1 mm的牙髓治疗中，具有Co-Cr冠的桩核是有用的。在第二个研究年度，研究了循环荷载作用下的两种边缘设计，肩型和斜肩型。每个浸泡在37℃水中的试样都加300N、1hz、30万次的荷载。循环加载后再加静荷载，直至试件断裂。结果表明，Co-Cr顶在斜角肩型边缘设计中有效提高断裂强度，但在肩型边缘设计中无效。高度腐烂的牙髓治疗后的牙齿仍然难以人工修复其冠，并且通常表明冠的寿命很短。这项体外研究表明，在牙髓治疗后的严重情况下，薄层Co-Cr的有效性。

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.