Libman W J, Nicholls J I
Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle 98195, USA.
Int J Prosthodont. 1995 Mar-Apr;8(2):155-61.
Twenty-five extracted human central incisors were divided into five groups and prepared for complete cast crowns. Test teeth had cast dowel cores fabricated with the ferrule height varying from 0.5 to 2.0 mm in 0.5-mm increments. The five control teeth did not have cast dowel cores. A 4.0-kg load was applied to each of the restored teeth at an angle of 135 degrees to the long axis of each tooth. This load was applied cyclically at a rate of 72 cycles per minute. The load application point was predetermined by a waxing jig that was used to wax all crowns. The primary variable was the ferrule length. The independent variable was the number of load cycles required to create preliminary failure. Preliminary failure was defined here as the loss of the sealing cement layer between crown and tooth. An electrical resistance strain gauge was used to provide evidence of preliminary failure. The results of this study showed that the 0.5 mm and 1.0 mm ferrule lengths failed at a significantly lower number of cycles than the 1.5 mm and 2.0 mm ferrule lengths and control teeth.
25颗拔除的人类中切牙被分为五组，并预备制作全冠。测试牙制作铸造桩核，桩核高度以0.5毫米的增量从0.5毫米变化到2.0毫米。五颗对照牙未制作铸造桩核。对每颗修复牙以与牙长轴呈135度角施加4.0千克的负荷。该负荷以每分钟72次循环的速率循环施加。负荷施加点由用于制作所有全冠的蜡型夹具预先确定。主要变量是桩核长度。自变量是产生初步破坏所需的负荷循环次数。此处将初步破坏定义为全冠与牙齿之间封闭粘结剂层的丧失。使用电阻应变仪来提供初步破坏的证据。本研究结果表明，0.5毫米和1.0毫米的桩核长度在显著低于1.5毫米和2.0毫米桩核长度以及对照牙的循环次数时发生破坏。
