The corrosive effects of sodium hypochlorite on nickel-titanium endodontic instruments: assessment by digital scanning microscope

AIM: Prolonged contact (several hours) of nickel-titanium (NiTi) endodontic instruments with sodium hypochlorite has a considerable corrosive effect which reduces the instruments' resistance to fractures. The aim of this study was to verify whether short-term contact (several minutes, as is the case in clinical practice) produces the same effects. METHODS: Using a digital scanning microscope, the blade surfaces of three groups of ProTaper instruments were examined, particularly of the #1 Shaping File. The blade's file (but not their handles) were soaked in sodium hypochlorite heated to 50 degrees C for three different times compatible with times in clinical practice, rather for 2, 5 and 10 minutes; the files were then compared with a control group. RESULTS: The micro-photographs did not reveal any appreciable signs of corrosion on the file blades. CONCLUSIONS: It is evident, therefore, that using sodium hypochlorite as an irrigating solution in root canals, where it comes into contact with NiTi rotary endodontic instruments, does not alter the surface structure of the files through corrosion. Thus it is possible to conclude that, considering the length of time used in clinical practice, sodium hypochlorite does not cause any increase of risk of fracture to Ni-Ti rotary instruments.