Impact of sodium hypochlorite and sterilization on R-Motion reciprocating file cyclic fatigue resistance

INTRODUCTION. Chemical exposure and sterilization may influence the fatigue behavior of nickel-titanium endodontic instruments. AIM. To evaluate the effects of immersion in 2.5% sodium hypochlorite and autoclave sterilization on dynamic cyclic fatigue resistance of R-Motion files. MATERIALS AND METHODS. Eighty R25 instruments (25/.06) were allocated to four groups ( n = 20): untreated control, autoclave sterilization, immersion in 2.5 mL of 2.5% NaOCl for 3 minutes, and immersion followed by sterilization. Dynamic fatigue was tested in a metallic canal with a 45° curvature and a radius of 6.06 mm. Time to fracture and fragment length were recorded. RESULTS. No significant differences were found for time to fracture ( p = 0.149; effect size = 0.431; power = 0.899) or fragment length ( p = 0.655; effect size = 0.118; power = 0.120). CONCLUSION. Under the tested conditions, NaOCl exposure, sterilization and their combination did not significantly change cyclic fatigue resistance relative to untreated instruments.