Effect of Sodium Hypochlorite and Hypochlorous Acid Solutions on the Cyclic Fatigue Resistance of Waveonegold, K3XF and Hyflex-EDM: A Study of Metallurgical Properties

The presented work was focused on investigating the effects of sodium-hypochlorite (NaOCl) and hypochlorous-acid (HOCl) solutions on the dynamic cyclic fatigue resistance of WaveOneGold (WOG), K3XF and Hyflex-EDM (HEDM) nickel-titanium (Ni-Ti) instruments. A total of 141 Ni-Ti instruments were included in the study, 45 of each file for cyclic fatigue testing and two for metallurgical analysis. The NiTi instruments were rotated in an artificial canal that was immersed in three different solutions [2.5% NaOCl, HOCl or distilled water (DW)] at body temperature until fracture occurred and the time to fracture (TtF) in seconds was recorded. Fractured and unused files were analysed by scanning-electron-microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and a microhardness tester. The mean data were analyzed statistically using Kruskal-Wallis, and post hoc Mann-Whitney-U test. The TtF of the HEDM was statistically significantly higher than that of WOG and K3XF for all solutions. It was found that 2.5% NaOCl and HOCl solutions reduced the TtF of the WOG, but had no significant effect on the K3XF and HEDM. By EDS analysis, it was determined that titanium-oxide compounds were formed on the file surfaces at most in 2.5% NaOCl solution. The highest hardness value was K3XF, and the lowest hardness value belonged to the HEDM instrument. The HOCl solution can be used as an alternative irrigation solution as it is less corrosive to the instruments compared to than NaOCl solution.