Effect of autoclave sterilisation and heat activated sodium hypochlorite irrigation on the performance of nickel-titanium rotary files against cyclic fatigue

The present study aims to assess the impact of heat-activated sodium hypochlorite (NaOCl) and/or autoclave sterilisation on the cyclic fatigue resistance (CFR) of heat-treated nickel-titanium rotary files used in root canal treatment. The CFR of One Curve (OC) files was evaluated under the following conditions: as received (Group 1; control), immersion in NaOCl at 23 +/- 1oC (Group 2), immersion in NaOCl at 60 +/- 1oC (Group 3), autoclave sterilisation at 135 1oC (Group 4), combined treatment of autoclave sterilisation and immersion in NaOCl at 23 +/- 1oC (Group 5), and combined treatment of autoclave sterilisation and immersion in NaOCl at 60 +/- 1oC (Group 6). A simulated root canal in a zirconia block was utilised to test the performance of the files. All the types of treatments resulted in significant reductions in fracture resistance of the OC files. Immersion of the files in NaOCl at 23oC revealed the smallest reduction, while combined treatment of autoclaving and immersion in NaOCl at 60oC caused the greatest reduction. Autoclave sterilisation or exposure of OC files to 2.5% NaOCl adversely affect the cyclic fatigue life and increasing solution temperature or combined treatment caused additionally significant reduction in CFR.