Cyclic fatigue comparison among endodontic instruments with similar cross section and different surface coating

BACKGROUND: The aim of this study was to analyze the influence of rotary instruments' geometry and surface titanium-nitride (TiN) treatment on the fatigue fracture, through the comparison of cyclic fatigue resistance of two endodontic systems that have similar cross-sectional design and different surface coating.METHODS: In this study 130 Mtwo (10/.04; 15/.05; 20/.06; 25/.06; 30/.05; 35/.04; 40/.04) and Easy Shape (15/.04; 20/.05; 25/.06; 30/.05; 35/.04; 40/.04) were tested for cyclic fatigue resistance. Time to fracture (TtF) was determined by counting the seconds of continuous rotation until final fracture in an artificial canal with 60 degrees angle and a 5 mm radius of curve. The fracture surface of each fragment was examined with a scanning electron microscope (SEM). Data were subjected to one-way analysis of variance (ANOVA) and Tukey post-hoc tests.RESULTS: Mtwo perform a significantly (P<0.001) higher number of cycles to fracture (NCF) compared with Easy Shape of the same size and taper. The comparison between Mtwo and Easy Shape instruments with the same taper showed higher TtF values of Mtwo files than the Easy Shape ones (P<0.001) while there were no differences among Mtwo and Easy Shape instruments with the same tip, (P>0.05).CONCLUSIONS: Mtwo exhibit a higher NCF thanks to the smaller metal volume contained in their core. Titanium-nitride coating does not influence the performance of Easy Shape instruments on static test of cyclic fatigue.