Cyclic Fatigue Resistance of Four Nickel-Titanium Rotary Instruments: A Comparative Study

Aim. Aim of the study was to investigate the cyclic fatigue resistance of four different nichel – titanium rotary (NTR) instruments produced by a new method or traditional grinding processes.Methods. In the present study four different NTR instruments from different brands, of identical sizes (.06 taper and 0.25 tip diameter) were selected and evaluated: group 1. Twisted File (SybronEndo, Orange, CA, USA) produced by a new thermal treatment of nichel – titanium alloy; group 2. (Revo S SU, MicroMega, Besancon, France); group 3. Mtwo (Sweden-Martina, Padova, Italy) and group 4. (BioRaCe BR3, FKG, La Chaux de Fonds, Switzerland,) produced by traditional grinding processes. Twenty NTR file from each manufacturer were tested for cyclic fatigue resistance, resulting in a total of 80 instruments. Tests were performed by a cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals with 60 degree angle of curvature and 5 mm radius of curvature. The instruments were rotated at a constant speed of 300 rpm. All instruments were rotated until fracture occurred. The time to fracture (TtF) from the start of the test until the moment of file breakage was recorded with a chronometer. The length of the fractured tip was also recorded for each instrument. Data were subjected to one-way analysis of variance (ANOVA).Results. Group 1 (Twisted File) showed the highest value of TtF means. Cyclic fatigue resistance of Twisted File was significantly higher than group 2 (Revo S SU) and 4 (BioRace BR3) (P<0.05), while no significant differences were founded between group 1 (Twisted File) vs 3 (Mtwo) or group 2 (Revo S SU) vs 4 (BioRaCe BR3) (P>0.05).Conclusions. Twisted File 25.06 had the best absolute TtF values. The cyclic fatigue resistance of Twisted File was significantly more than those produced with the traditional grinding process except of Mtwo files.