Impact of sodium hypochlorite irrigant on fatigue resistance of different nickel-titanium instruments

Aim: The purpose of this study was to investigate the resistant of three NiTi files, ProTaper (PTN), Hyflex EDM and 2Shape (TS) to cyclic fatigue after being immersed in a 2.5 percent NaOCl irrigant solution in different times (1&5 minutes) at 37°C. Materials and Methods: Seventy-two heat treated files used in this study, divided into three main groups (n=24) according to their metallurgy group-1: PTN, group-2: Hyflex EDM and group-3: TS files each group then subdivided into three subgroups, subgroup-1 immersed in 2.5 percent NaOCl for 1minute at 37°C subgroup-2 immersed in 2.5 percent NaOCl for 5 minutes at 37°C and subgroup-3 did not undergo any immersion as a control group. All files were put through cyclic fatigue testing in a digital water bath at 37°C to imitate body temperature in a stainless-steel artificial canal. The time to fracture was recorded in minutes, then by multiplying the time to fracture by the rotations per minute, the number of cycles to fracture (NCF) was calculated. The data were checked for normality before running a one-way ANOVA with a post hoc test.