Evaluation of the Cyclic Fatigue Resistance of 2Shape, ProTaper Gold and Vortex Blue Rotary NiTi Files in curved Canals (A Comparative In-Vitro Study)

Abstract

The aim of this study was to compare the cyclic fatigue resistance of three different thermomechanically treated rotary NiTi instruments namely, 2Shape (TS), ProTaper Gold (PTG) and Vortex Blue (VB) systems. Thirty six rotary NiTi instruments were divided into the 3 groups of TS (25/0.06), PTG (25/0.08) and VB (25/0.06) (n=12). These instruments were allowed to rotate in a custom made model with a 60˚ angle of curvature and 5mm radius of curvature until fracture occurred. The model was immersed in an acrylic container filled with 2.5% NaOCl solution set at intracanal temperature (35˚C ± 2˚C). Following the fracture, time to fracture was recorded and the number of cycles to failure (NCF) was then calculated. The length of the fractured segments was measured using a digital caliper and scanning electron microscope (SEM) examination was also performed. The data were statistically analyzed using Kruskal-Wallis and Dunn’s tests with the significance level set at P ≤ 0.05. The PTG group showed statistically significant highest NCF followed by the VB group and TS group which had the lowest statistically significant NCF. Concerning time to fracture, PTG also showed the longest fatigue life, while there was no significant difference among VB and TS groups. Both the PTG and TS groups exhibited no significant difference regarding the length of the fractured segment. However, they had statistically significant longer fragment length compared to the VB group. SEM analysis revealed typical features of cyclic fatigue failure.