Effects of Simultaneous Liquid or Gel Sodium Hypochlorite Irrigation on the Cyclic Fatigue of Two Single-File Nickel-Titanium Instruments

Abstract

Featured Application The proposed customized device could represent a way to standardize cyclic fatigue tests of nickel-titanium instruments in the presence of irrigant solutions. Future studies could pursue laboratory investigations on nickel-titanium instrument surface exposed to irrigant solutions under these standardized methodological conditions. 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 degrees C and 37 degrees C, respectively. Groups 2 and 5 included files activated with liquid NaOCl at 20 degrees C and 37 degrees C, respectively. Groups 3 and 6 consisted of instruments tested with NaOCl gel at 20 degrees C and 37 degrees 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 degrees C (p < 0.05). At 20 degrees 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 degrees 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.