Fatigue Resistance of Nickel-titanium Instruments Exposed to High-concentration Hypochlorite

摘要

Abstract Introduction The purpose of this study was to introduce a new fatigue test model that simulates the clinical situation for evaluating the corrosion effect of 5.25% sodium hypochlorite (NaOCl) on nickel-titanium (NiTi) files and to evaluate the effect of 3 different temperatures (22°C, 37°C, and 60°C) on the cyclic fatigue of these files. Methods Three NiTi files (size 25/.04), K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and Vortex (Dentsply Tulsa Dental Specialties, Tulsa, OK), were subjected to cyclic fatigue tests inside a novel artificial ceramic canal with a curvature of 60° and a 5-mm radius. A 19-mm-long file segment from the tip was introduced into the canal and immersed in water or 5.25% NaOCl at 3 different temperatures, and the number of revolutions to fracture (N f ) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. Data were analyzed using univariate analysis of variance with the significance level at 0.05. Results The N f of Vortex files was the highest followed by K3XF and K3 ( P ? f of all files was highest at 22°C and lowest at 60°C ( P ? f was detected in Vortex files between 22°C and 37°C. The N f of all files in 5.25% NaOCl was shorter than that in water although there was no statistically significant difference. No pitting or crevice corrosion was observed on the fracture surface. Conclusions NaOCl, 5.25%, does not significantly affect the fatigue behavior of NiTi files. The fatigue resistance should be tested under specific temperature conditions. The austenite finish temperature of a file is important in determining the fracture risk at body temperature. Highlights ? A new fatigue test (in zirconium oxide) model that better simulates the clinical situation for the evaluation of the corrosion effect by 5.25% sodium hypochlorite (NaOCl) on nickel-titanium (NiTi) files is introduced. ? The effect of 3 different temperatures (22°C, 37°C, and 60°C) on the cyclic fatigue life of conventional superelastic and heat-treated NiTi files is evaluated. ? The fatigue life of NiTi files in 5.25% NaOCl is only slightly shorter than in water, with no statistically significant difference. ? The Vortex file with a reported high austenite finish temperature shows only a slight reduction of cyclic fatigue resistance at body temperature, whereas at 60°C the fatigue resistance is greatly reduced. ? Contrary to the Vortex file, the fatigue resistance of the K3 and K3XF files decreases clearly at body temperature. ]]>