On the effect of sodium hypochlorite solution on NiTi

NiTi alloys are commonly used as materials for medical implants or medical devices due to their good biocompatibility and pseudoelasticity. In this context, the use of disinfectant solutions for irrigation requires careful consideration. The use of sodium hypochlorite (NaClO) for cleaning NiTi files, e.g. in root canal treatments, was studied and results showed pronounced differences regarding the effect of NaClO on NiTi. The observations range from non-detectable reaction to severe attack resulting in the formation of black particles and disintegration of the material. So far, the reasons for this asymmetric behavior remain to be clarified. The purpose of this study is to address the unresolved issues related to the behavior of NiTi in the presence of NaClO. This includes the investigation of the influence of thermal treatment, surface finishing and sample geometry. Pre-treated samples were immersed in NaClO for defined periods of time and it was observed that NiTi with thermally grown oxide layers is more susceptible to a reaction and formation of black flocculent residue. However, some heat-treated samples remained stable, confirming that the presence of an oxide layer is not a definite criterium for judging the material’s behavior. To gain more information regarding the underlying reaction, the black residue was subjected to drying and analyzed by X-ray diffraction (XRD) and the topography of the sample surfaces were analyzed by scanning electron microscopy (SEM). As a result, the conditions that lead to a detrimental effect are narrowed down, what should help to clarify the details in future work.