Effect of a novel motion and simultaneous irrigation on the cyclic fatigue resistance of Hyflex EDM OneFile

The aim of this study was to assess the cyclic fatigue resistance of a single-file system (i.e., Hyflex EDM OneFile), during continuous rotation and reflex dynamic motion with and without irrigation. Cyclic fatigue tests were conducted on 48 new Hyflex EDM One files using two different motions, with and without irrigation. The files were randomly assigned to four groups (n = 12) based on the tested motion and irrigation conditions: continuous rotation and the novel kinematics ReFlex Dynamic motion, with and without irrigation. The dynamic fatigue resistance was measured as the number of cycles to fracture (NCF) in an artificial zirconium canal with a 60 degrees angle and a 5 mm radius of curvature at an intracanal temperature. The results were analyzed using the non-parametric Mann-Whitney test, with a significance level established at 5% (p < 0.05). The fractured instruments were examined with a scanning electron microscope. The instruments activated in continuous rotation, irrespective of irrigation conditions, demonstrated significantly higher NCF compared to those in ReFlex Dynamic (p < 0.05). Irrigation significantly impacted the cyclic fatigue resistance of Hyflex EDM in ReFlex Dynamic motion (p < 0.05), while it did not influence the resistance of files tested under continuous rotation (p > 0.05). Within the limitations of this in vitro study, HyFlex EDM One files tested under continuous rotation showed greater resistance to cyclic fatigue compared to those tested with ReFlex Dynamic motion, regardless of irrigation. Continuous hypochlorite irrigation enhanced the cyclic fatigue resistance only of the files tested in ReFlex Dynamic motion.