Abstract
To evaluate the effect of simultaneous liquid or gel sodium hypochlorite (NaOCl) irrigation on cyclic fatigue of F6 SkyTaper (F6ST) and OneCurve (OC) single files, 180 new 25/0.06 F6ST and OC files were divided into 6 groups (n = 15) for each brand. Groups 1 and 4 included new instruments not exposed to NaOCl at 20 °C and 37 °C, respectively. Groups 2 and 5 included files activated with liquid NaOCl at 20 °C and 37 °C, respectively. Groups 3 and 6 consisted of instruments tested with NaOCl gel at 20 °C and 37 °C, respectively. Instruments were subjected to a fatigue test using a novel customized device. Data were expressed as time to fracture (TtF) and statistically analyzed (p < 0.05) after checking their normality through the Shapiro–Wilk test. Because they were normally distributed, 2-way analyses of variance (ANOVA) and the Tukey multiple comparison post-hoc test were used. Time to fracture of all tested instruments decreased at 37 °C (p < 0.05). At 20 °C, NaOCl improved TtF of F6ST and OC (p < 0.05). NaOCl liquid increased TtF of F6ST (p < 0.05) in comparison with gel, while there was no difference between the two formulations for OC. At 37 °C, both NaOCl formulations had no significant influence on TtF for F6ST, while they increased TtF of OC (p < 0.05). NaOCl improved the cyclic fatigue resistance of OC, independently of the temperature, while for F6ST the negative impact of higher temperature reduced the irrigant benefits.
Highlights
Nickel-titanium (NiTi) alloy is widely employed in endodontics due to its properties of superelasticity and shape memory [1]
NiTi instruments are subjected to an unexpected separation, due to the cyclic fatigue and torsional fracture, during the clinical use [2,3]
All instruments have a continuous taper of 0.06 and an S-shaped cross-section [13]. Another single-file system is the OneCurve endodontic file (OC; Micro Méga, Besançon, France), made from a NiTi alloy that receives a patent-protected heat treatment (C-Wire) which provides to the file a shape-memory effect
Summary
Nickel-titanium (NiTi) alloy is widely employed in endodontics due to its properties of superelasticity and shape memory [1]. Sci. 2020, 10, 6666 transformation, favoring a high percentage of the martensitic phase to increase the flexibility of heat-treated NiTi [5,6]. Single-file systems have been presented to facilitate the instrumentation protocols and minimize mechanical stresses [10]. Lemgo, Germany) is an example of a single-file system made by traditional NiTi alloy available in four different sizes, including 25 size. All instruments have a continuous taper of 0.06 and an S-shaped cross-section [13]. Another single-file system is the OneCurve endodontic file (OC; Micro Méga, Besançon, France), made from a NiTi alloy that receives a patent-protected heat treatment (C-Wire) which provides to the file a shape-memory effect. OC files present a tip size of 25 and a constant taper (6%) with a variable cross-section [12]
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