Objective: To evaluate cyclic fatigue and torsional resistance of Reciproc Blue R25 (VDW, Munich, Germany), WaveOne Gold Primary (Dentsply Maillefer, Ballaigues, Switzerland), ProDesign R (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil), and X1 Blue File (MK Life, Porto Alegre, Brazil) nickel titanium (NiTi) martensite reciprocating instruments. 

Methods: In each group, ten instruments were tested for cyclic fatigue resistance using a stainless-steel artificial canal (curvature angle of 80° and radius of 3 mm) and ten instruments for torsional failure according to ISO 3630-1 standard. The surface of the fractured instruments was examined under scanning electron microscopy (SEM) at ×250 magnification. The results were compared statistically with one-way ANOVA and post hoc Tukey tests and the alpha-type error was set at 5%.

Results: X1 blue file and ProDesign Rinstruments showed highest time to fracture than Reciproc Blue and Wave One Gold (P<0.05). However, no differences were found between X1 Blue File and ProDesign R (P>0.05). In addition, Reciproc Blue demonstrated highest time to fracture than WaveOne Gold (P<0.05). The lowest torsional resistance (1.0}0.2 N.cm) and angle of rotation (412o}46) was observed in the ProDesign R group (P<0.05). SEM analyses of fractured surfaces showed a crack initiation area and overload fast fracture zone after cyclic fatigue test, and concentric abrasion marks with microvoids at the centre of rotation after torsional failure experiment.

Conclusion: Overall, X1 Blue File and ProDesign R showed higher cyclic fatigue resistance than Reciproc Blue and WaveOne Gold instruments, while ProDesign R had the lowest torsional resistance and angular rotation values to fracture. SEM analysis of all instruments demonstrated typical failures features in both cyclic fatigue and torsional failure tests.

Keywords: Cyclic fatigue, dental instruments, torsional force