Abstract : Background: NiTi instruments have a risk of separation due to torsional or flexural fatigue (cyclic fatigue). Chemo-mechanical preparation and cleaning procedures cause the corrosion of endodontic instruments that may weaken the fracture resistance of the instruments.
Aim of the Study: To assess resistance to cyclic fatigue of Reciproc files R25 after immersion in different concentrations of sodium hypochlorite in conditions similar to those used in clinical practice.
Materials and Methods: The study sample included 40 new Reciproc R25 files according to the G-power program and divided randomly into four groups according to NaOCl concentration (n=10). Files were immersed in NaOCl for 10 minutes at room temperature and for 16mm length as following: Group A no immersion (control), Group B (1% NaOCl), Group C (2.5% NaOCl) and Group D (5.25% NaOCl). The cyclic fatigue resistance was tested in stainless steel artificial canal manufactured reproducing the instrument size and taper, with 120° angle of curvature and 2.5 radius of curvature. The Time to Fracture (TtF) was statically analyzed.
Results: According to statistical data for analytical study, the mean of Time to Fracture (TtF) group A control, B, C and D was170.77,153.10,142.32, and 132.59 respectively. One-way ANOVA test indicated no significant differences in mean of TtF between NaOCl concentration groups. Resistance to cyclic fatigue of R25 was not affected by the concentration of NaOCl used in this study (P>0.05).
Conclusions: Using different concentrations of NaOCl for 10 minutes did not reduce the resistance to cyclic fatigue of Reciproc R25 files.
Keywords: Cyclic fatigue, NaOCl, Reciproc R25.