Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada; Department of Materials Engineering, The University of British Columbia, Vancouver, Canada.
Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada.
J Endod. 2018 Apr;44(4):643-647. doi: 10.1016/j.joen.2017.12.002. Epub 2018 Jan 12.
The purpose of this study was to evaluate the effect of a low amount of torsional preloading on the fatigue life and different degrees of cyclic fatigue on torsional failure of HyFlex EDM (EDM; Coltene-Whaledent, Allstetten, Switzerland) and HyFlex CM (CM; Coltene-Whaledent) instruments.
EDM and CM files were used. The fatigue resistance was examined in a 5-mm radius and 60° single curve, and the mean number of cycles to failure (N) was recorded. The torque and rotation angles at failure of the instruments were measured according to ISO 3630-1. New files were precycled to 0%, 50%, and 75% of the N, and torsional tests were then performed. Other new files were preloaded at 5%, 15%, 25%, and 50% of the mean rotation angles before the fatigue test. The fracture surfaces of the fragments were examined under a scanning electron microscope.
The fatigue resistance of EDM instruments was higher than that of CM instruments (P < .05). The torque and angle of rotation at fracture of the files were similar. Torsional preloading lowered the N of EDM at 15% preloading (P < .05) and the N of CM at 50% preloading (P < .05). However, the N of EDM files even with 50% torsional preloading was significantly higher than unused CM files (P < .05). Fatigue prestressing even at 75% had no negative effect on the torque and rotation angle of the EDM files. Moderate precycling (50%) of EDM files increased their torsional resistance. The fractographic patterns corresponded to the pattern defined by the last stage test.
A low amount (15%) of torsional preloading reduced the fatigue resistance of EDM files, whereas even extensive (75%) precyclic fatigue was not detrimental to their torsional resistance.
本研究旨在评估低扭转预加载量对 HyFlex EDM（EDM；Coltene-Whaledent，Allstetten，瑞士）和 HyFlex CM（CM；Coltene-Whaledent）器械的疲劳寿命和不同程度的循环疲劳以及扭转失效的影响。
使用 EDM 和 CM 文件。在半径为 5mm 和 60°的单个曲线上检查疲劳阻力，并记录失效的平均循环次数（N）。根据 ISO 3630-1 测量器械失效时的扭矩和旋转角度。将新文件预循环至疲劳试验的 0%、50%和 75%的 N，然后进行扭转试验。其他新文件在疲劳试验前以 5%、15%、25%和 50%的平均旋转角度进行预加载。使用扫描电子显微镜检查碎片的断裂表面。
EDM 器械的疲劳阻力高于 CM 器械（P<.05）。文件断裂时的扭矩和旋转角度相似。扭转预加载会降低 15%预加载的 EDM 的 N（P<.05）和 50%预加载的 CM 的 N（P<.05）。然而，即使在 50%的扭转预加载下，EDM 文件的 N 仍显著高于未使用的 CM 文件（P<.05）。即使在 75%的疲劳预加载下，也不会对 EDM 文件的扭矩和旋转角度产生负面影响。EDM 文件的适度预循环（50%）会增加其扭转阻力。断口形态与最后阶段试验定义的形态相对应。
少量（15%）的扭转预加载会降低 EDM 文件的疲劳阻力，而即使是广泛的（75%）预循环疲劳也不会对其扭转阻力产生不利影响。
