Evaluation of cyclic flexural fatigue resistance of 25/0.04 and 25/0.06 twisted file rotary nickel-titanium endodontic instruments

Twisted files (TFs) are rotary nickel‐titanium (NiTi) instruments that are produced with a newly developed manufacturing process that is supposed to improve their properties, especially flexibility and resistance to cyclic flexural fatigue failure. The aim of this study was to study the cyclic flexural fatigue failure resistance of tip size International Standards Organization 25 TFs with two tapers 0.04 and 0.06 and to compare them with the Profile (PF) rotary NiTi files of similar tip size and taper. Four groups of fifteen files were used in this study. TF (25/0.04), TF (25/0.06), PF (25/0.04) and PF (25/0.06) were tested using the cyclic flexural fatigue testing device. The time to failure during cyclic flexural fatigue testing was recorded. The mean time required for the instrument to fail under cyclic flexural fatigue testing was 235.5 ± 68 s for 25/0.04 TF, 188.5 ± 75 s for 25/0.06 TF, 180.3 ± 102 s for 25/0.04 PF and 156.3 ± 17 s for 25/0.06 PF. The difference between the time to failure of 25/0.04 TF and 25/0.06 TF was not statistically significant. The difference between the time to failure of TF and PF of similar tip size and taper was not statistically significant. The findings of this study indicate that size 25/0.04 and 25/0.06 TFs had similar resistance to cyclic flexural fatigue failure. In addition, TFs were not superior, in terms of resistance to cyclic flexural fatigue failure, to PF of similar tip size and taper.