Lindauer S J, Macon C R, Browning H, Rubenstein L K, Isaacson R J
Department of Orthodontics, School of Dentistry, Medical College of Virginia, Virginia Commonwealth University, Richmond.
Am J Orthod Dentofacial Orthop. 1994 Nov;106(5):481-6. doi: 10.1016/S0889-5406(94)70070-2.
The fracture resistance of ceramic brackets to orthodontic activations has been incorrectly estimated by previous investigations that have reported second order loads in terms of force magnitudes rather than moments. Because force magnitudes alone do not reflect the influence of distance from the site of force application on total load, it is impossible to apply previous results to actual clinical situations. The purpose of this study was to determine the average moments (in gram-millimeters) necessary to fracture various ceramic brackets subjected to second order tipping activations and compare them with actual clinical loads. Central and lateral incisor ceramic brackets from seven manufacturers were subjected to mesial-distal tipping arch wire activations at two speeds of load application with a testing apparatus designed for that purpose. Significant differences in fracturability among the brackets of various manufacturers and between central and lateral incisor brackets were found. There were no differences related to the speed of load application. Once the influence of bracket width was considered, the differences in fracture resistance between central and lateral incisor brackets were no longer apparent. Second order activations required to fracture the ceramic brackets in this study were all much greater than measured clinical orthodontic loads. It is unlikely that second order arch wire activations are a significant cause of ceramic bracket failure.
以往的研究在报告二级载荷时采用力的大小而非力矩，从而错误地估计了陶瓷托槽对正畸激活的抗断裂性。由于仅力的大小不能反映力作用点到施力部位的距离对总载荷的影响，因此无法将以往的结果应用于实际临床情况。本研究的目的是确定在二级倾斜激活下使各种陶瓷托槽断裂所需的平均力矩（克毫米），并将其与实际临床载荷进行比较。使用为此设计的测试设备，以两种加载速度对来自七个制造商的中切牙和侧切牙陶瓷托槽进行近远中倾斜弓丝激活。发现不同制造商的托槽之间以及中切牙和侧切牙托槽之间在可断裂性方面存在显著差异。加载速度没有差异。一旦考虑托槽宽度的影响，中切牙和侧切牙托槽之间的抗断裂性差异就不再明显。本研究中使陶瓷托槽断裂所需的二级激活均远大于测量的临床正畸载荷。二级弓丝激活不太可能是陶瓷托槽失败的重要原因。
