Electropolishing enhances the resistance of nickel-titanium rotary files to corrosion-fatigue failure in hypochlorite

Abstract

Introduction: The aim of this study was to examine the fatigue behavior, especially at the low-cycle fatigue (LCF) region, of an experimentally electropolished FlexMaster and a commercial electropolished nickel-titanium (NiTi) instrument (RaCe) in a corrosive environment. Methods: A total of 90 NiTi rotary instruments were subjected to rotational bending at various degrees of curvatures while immersed in 1.2% sodium hypochlorite solution until broken. The maximum surface strain amplitude, calculated from the curvature of the instrument and the diameter of the cross section at break, was plotted against the LCF life. The results were compared with data for a non-electropolished commercial product tested by using the same methodology. Results: The fatigue life of both instruments generally declined with increasing surface strain amplitude; there was a significant difference between the 2 instruments. Comparing the surface-treated FlexMaster with its commercially available non-electropolished counterpart, an improved resistance to fatigue breakage as a result of electropolishing was noted (P < .05). Conclusions: The LCF life of a NiTi instrument rotating with a curvature in a corrosive environment is enhanced by electropolishing. The design, both cross-sectional and longitudinal, appears to have an effect on the fatigue behavior of NiTi rotary instruments. © 2010 American Association of Endodontists.