Effects of Sodium Hypochlorite on Corrosion Behavior and Cyclic Fatigue in Different Types of NiTi Rotary Endodontic Instruments

Sodium hypochlorite (NaOCl), as the most commonly used irrigant solution, offers strong antibacterial and organic tissue dissolving properties and has the potential to express a strong corrosive effect. The aim of the study was to evaluate the effects of NaOCl on corrosion behavior and cyclic fatigue in five different types of NiTi rotary endodontic instruments. The study examined: ProTaper Universal, ProTaper Next, Twisted File, HyFlex CM, and BioRace, each with 24 samples. Each group was divided into a control subgroup and a subgroup exposed to electrochemical testing of corrosion in 5.25% NaOCl. All instruments were exposed to a cyclic fatigue test in artificial canals with a curvature angle of 60 degrees and radius of 2 mm. The corrosion potential of NaOCl was determined in all groups of instruments. ProTaper Universal had a significantly lower corrosion resistance than ProTaper Next (p < 0.05), Twisted File, BioRace, and HyFlex CM (p < 0.001). HyFlex CM showed significantly higher resistance to cyclic fatigue compared to all the other groups of instruments (p < 0.001). Surface corrosion reduced cyclic fatigue resistance in most of the instrument groups, except in heat-treated instruments with controlled memory. HyFlex CM has proven to have the highest resistance to corrosion and cyclic fatigue.