Shen Ya, Riyahi Abdullah Mahmoud, Campbell Les, Zhou Huimin, Du Tianfeng, Wang Zhejun, Qian Wei, Haapasalo Markus
Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, British Columbia, Canada; Department of Materials Engineering, The University of British Columbia, Vancouver, British Columbia, Canada.
Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, British Columbia, Canada.
J Endod. 2015 Apr;41(4):526-30. doi: 10.1016/j.joen.2014.10.008. Epub 2014 Nov 21.
The purpose of this study was to evaluate the effect of various degrees of cyclic fatigue on torsional failure and torsional preloading on the cyclic fatigue life of heat-treated K3XF nickel-titanium (NiTi) instruments (SybronEndo, Orange, CA).
The mean number of cycles until failure (Nf) of K3XF and K3 NiTi instruments was examined in a 3-point bending apparatus with a 7-mm radius and 45° curve. Torque and distortion angles at failure of new instruments and instruments stressed to 25%, 50%, and 75% of the Nf were measured according to ISO 3630-1. Other new files were preloaded at 25%, 50%, and 75% of the mean distortion angles before the fatigue test. After torsional preloading, the Nf was examined. The fracture surface of each fragment was examined with a scanning electron microscope.
The fatigue resistance of K3XF instruments was 2 times higher than that of K3 instruments (P < .05). The torque and angle of rotation at fracture of K3XF instruments were similar to those of K3 instruments. The 25%, 50%, and 75% torsional preloading significantly lowered the Nf of both K3 and K3XF instruments (P < .05). In the fatigue prestressed groups, K3 instruments with 75% preloading had significantly lower torque and distortion angles than unused K3 instruments (P < .05). The fractographic patterns corresponded to the pattern defined by the last stage test.
A low amount of torsional preloading reduced the fatigue resistance of K3 and K3XF instruments. A high amount of precycling fatigue significantly reduced the torsional resistance of K3 instruments. The torsional resistance of K3XF instruments was less affected by previous load cycling even after extensive precycling.
本研究的目的是评估不同程度的循环疲劳对热处理后的K3XF镍钛（NiTi）器械（SybronEndo，奥兰治，加利福尼亚州）扭转失效的影响，以及扭转预加载对其循环疲劳寿命的影响。
在半径为7毫米、弯曲角度为45°的三点弯曲装置中检测K3XF和K3镍钛器械直至失效的平均循环次数（Nf）。根据ISO 3630-1标准，测量新器械以及承受了Nf的25%、50%和75%应力的器械失效时的扭矩和变形角度。其他新锉在疲劳测试前以平均变形角度的25%、50%和75%进行预加载。扭转预加载后，检测Nf。用扫描电子显微镜检查每个碎片的断裂表面。
K3XF器械的抗疲劳性比K3器械高2倍（P <.05）。K3XF器械断裂时的扭矩和旋转角度与K3器械相似。25%、50%和75%的扭转预加载显著降低了K3和K3XF器械的Nf（P <.05）。在疲劳预加应力组中，预加载75%的K3器械的扭矩和变形角度显著低于未使用的K3器械（P <.05）。断口形貌模式与最后阶段测试所定义的模式相符。
少量的扭转预加载会降低K3和K3XF器械的抗疲劳性。大量的预循环疲劳会显著降低K3器械的抗扭性。即使经过大量预循环，K3XF器械的抗扭性受先前载荷循环的影响较小。
