Torsional and cyclic fatigue resistance of the new Hyflex EDM instruments and their comparison with Reciproc and WaveOne

Aim To investigate the torsional strength, angular rotation and cyclic fatigue resistance of the new Hyflex EDM OneFile, manufactured by CM-wire and a process novel to nickel-titanium (NiTi) file production called electrical discharge machining (EDM), and compare these findings with Reciproc R25 and WaveOne Primary (both made with M-wire).Methodology Thirty new Hyflex EDM OneFile, Reciproc R25 and WaveOne Primary files were tested for torsional and cyclic fatigue resistance. Cyclic fatigue testing was performed with theinstruments (n = 15 each) operating until fracture inside an artificial canal with 60° angle of curvature and 5 mm radius of curvature in continuous rotation at 500 RPM for Hyflex EDM and in the reciprocating motion for the Reciproc R25 and WaveOne Primary files as recommended by each manufacturer. The number of cycles to fracture (NCF) was determined by measuring the timeto fracture. Instruments (n = 15 each) were tested for torsional strengthand angular rotation to fracture following the ISO 3630-1 guideguidelinesby using a torsiometer. Kruskal-Wallis and Dunn’s multiple comparison post-hoc tests at 0.05 were used to evaluate all data. The fracture surface of each fragment was examined with a scanningelectron microscope (SEM).Results Cyclic fatigue resistance of Hyflex EDM was significantly higher than that of Reciproc R25 (P < .001). Reciproc R25 cyclic fatigue resistance was higher than WaveOne (P < .01). Hyflex EDM OneFile had a significantly higher angular rotation to fracture and lower maximum torsional strength than Reciproc R25 and WaveOne Primary (P < .05 and P < .001 respectively). No significant difference was found in the torque and angular rotation to fracture of the reciprocating instruments tested.Conclusions Hyflex EDM OneFile had higher cyclic fatigue and angular rotation, but lower maximum torque to fracture than Reciproc R25 and WaveOne Primary, due to their alloy and productionprocesses.Acknowledgements The authors thank engineer Calogero Sorcefrom the Univeristy of Catania for the support in the torsionaltests.