Department of General Surgery and Surgical-Medical Specialties, University of Catania, Catania, Italy.
Department of Dentistry, Universidad Cientifica del Sur, Lima, Perù.
J Endod. 2018 Apr;44(4):648-653. doi: 10.1016/j.joen.2017.12.011. Epub 2018 Feb 1.
The purpose of this study was to assess the effects of sodium hypochlorite (NaOCl) immersion and sterilization on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) rotary instruments.
Two hundred ten new 25/.06 Twisted Files (TFs; SybronEndo, Orange, CA) and Hyflex CM (Coltene Whaledent, Cuyahoga Falls, OH) files were divided into 7 groups (n = 15) for each brand. Group 1 (control group) included new instruments that were not immersed in NaOCl or subjected to autoclave sterilization. Groups 2 and 3 were composed of instruments dynamically immersed for 3 minutes in 5% NaOCl solution 1 and 3 times, respectively. Groups 4 and 5 consisted of instruments only autoclaved 1 and 3 times, respectively. Groups 6 and 7 recruited instruments that received a cycle of both immersion in NaOCl and sterilization 1 and 3 times, respectively. Instruments were subsequently subjected to a fatigue test. The surface morphology of fractured instruments was studied by field-emission scanning electron microscopy and x-ray energy-dispersive spectrometric (EDS) analyses. The means and standard deviations of the number of cycles to failure (NCF) were calculated and statistically analyzed using 2-way analysis of variance (P < .05).
Comparison among groups indicated no significant difference of NCF (P > .05) except for the groups of TFs sterilized 3 times without and with immersion in NaOCl (P < .05). HyFlex CM files exhibited higher cyclic fatigue resistance than TFs when files were sterilized 3 times, independently from immersion in NaOCl (P < .05). EDS analysis showed the presence of an oxide-rich layer on the Hyflex CM files' external surface. No morphologic or chemical differences were found between files of the same brand subjected to different treatments.
Repeated cycles of sterilization did not influence the cyclic fatigue of NiTi files except for TFs, which showed a significant decrease of flexural resistance after 3 cycles of sterilization. Immersion in NaOCl did not reduce significantly the cyclic fatigue resistance of all heat-treated NiTi files tested.
本研究的目的是评估次氯酸钠（NaOCl）浸泡和灭菌对热处理镍钛（NiTi）旋转器械的循环疲劳强度的影响。
将 210 个新的 25/.06 号 Twisted File（TF；SybronEndo，Orange，CA）和 Hyflex CM（Coltene Whaledent，Cuyahoga Falls，OH）器械分为每个品牌 7 组（n=15）。第 1 组（对照组）包括未浸泡在 NaOCl 或未进行高压蒸汽灭菌的新器械。第 2 组和第 3 组由分别动态浸泡在 5% NaOCl 溶液中 3 分钟的器械组成。第 4 组和第 5 组由仅分别高压蒸汽灭菌 1 次和 3 次的器械组成。第 6 组和第 7 组招募了分别接受 1 次和 3 次 NaOCl 浸泡和灭菌循环的器械。器械随后进行疲劳试验。通过场发射扫描电子显微镜和 X 射线能量色散谱（EDS）分析研究断裂器械的表面形态。使用 2 因素方差分析（P<.05）计算失效循环数（NCF）的平均值和标准差，并进行统计分析。
各组间比较发现，除未浸泡在 NaOCl 中 3 次高压蒸汽灭菌的 TF 组和浸泡在 NaOCl 中 3 次高压蒸汽灭菌的 TF 组之间（P<.05）外，NCF 无显著差异（P>.05）。HyFlex CM 器械在 3 次高压蒸汽灭菌时表现出比 TF 更高的循环疲劳强度，而与是否浸泡在 NaOCl 无关（P<.05）。EDS 分析表明，HyFlex CM 器械外表面存在富含氧化物的层。在同一品牌的器械接受不同处理时，未发现形态或化学差异。
除 TF 外，重复的灭菌循环对 NiTi 器械的循环疲劳强度没有影响，而 TF 在 3 次灭菌循环后弯曲阻力明显下降。浸泡在 NaOCl 中并没有显著降低所有测试的热处理 NiTi 器械的循环疲劳强度。
