Cyclic fatigue resistance of four nickel-titanium rotary instruments: a comparative study

Aims. The aim of this study is to investigate cyclic fatigue resistance of four nickel – titanium rotary (NTR) instruments produced by a new method or traditional grinding processes. Methods. Four NTR instruments from different brands were selected: group 1. Twisted File pro- duced by a new thermal treatment of nickel – tita- nium alloy; group 2. Revo S SU; group 3. Mtwo and group 4. BioRaCe BR3 produced by traditional grinding processes. A total of 80 instruments (20 for each group) were tested for cyclic fatigue resistance inside a curved artificial canal with a 60 degree angle of curvature and 5 mm radius of curvature. Time to fracture (TtF) from the start of the test until the mo- ment of file breakage and the length of the fractured tip was recorded for each instrument. Means and standard deviations (SD) of TtF and fragment length were calculated. Data were subjected to one-way analysis of variance (ANOVA). Results. Group 1 (Twisted File) showed the high- est value of TtF means. Cyclic fatigue resistance of Twisted File and Mtwo was significantly higher than group 2 (Revo S SU) and 4 (BioRace BR3), while no significant differences were found between group 1 (Twisted File) and 3 (Mtwo) or group 2 (Revo S SU) and 4 (BioRaCe BR3). Conclusions. The cyclic fatigue resistance of Twist- ed File was significantly frigher than instruments produced with traditional grinding process except of Mtwo files.