Aim: To compare the cyclic fatigue resistance of three thermomechanically treated rotary nickeltitanium instruments, 2Shape (TS; Micro-Mega, Besancon, France), ProTaper Gold (PTG; Dentsply Maillefer, Baillagues, Switzerland) and Vortex Blue (VB; Dentsply Tulsa Dental Specialties, Tulsa, OK, USA), under intracanal conditions.
Materials and methods: A total of 36 rotary nickel-titanium instruments of (12 TS [25/0.06]; 12 PTG [25/0.08]; 12 VB [25/0.06]) were rotated in a custom-made model with a 60-degree angle of curvature and 5-mm radius of curvature until fracture occurred. The model was immersed in an acrylic resin container filled with 2.5% sodium hypochlorite (NaOCl) solution set at intracanal temperature (35°C ± 2°C). Time to fracture was recorded, then the number of cycles to failure was calculated. The length of the fractured segments was measured using a digital caliper and scanning electron microscopy was also performed. The data were statistically analysed using a Kruskal-Wallis and Dunn test with the significance level set at P ≤ 0.05.
Results: The PTG group showed the highest statistically significant number of cycles to failure followed by the VB and TS groups, respectively (P ≤ 0.001). Both the PTG and TS groups exhibited no statistically significant difference regarding the length of the fractured segments (P ≥ 0.05); however, they had statistically significant longer fragments compared to the VB group (P ≤ 0.007). Scanning electron microscopy analysis revealed typical features of cyclic fatigue failure.
Conclusions: The PTG system had the highest cyclic fatigue resistance followed by the VB system. The T-wire technology of the TS system showed the lowest resistance to cyclic fatigue.