Evaluation of the cyclic fatigue resistance of rotary pathfinding instruments made of nickel-titanium (NiTi) alloys with different heat treatments

Aim: The aim of this study was to compare the cyclic fatigue resistance of rotary pathfinding instruments made of nickel-titanium (NiTi) alloys submitted to different heat treatments.

Materials and Methods: Eighty NiTi endodontic files were divided into four study groups, as follows: Scout Race 15.02 (FKG Deintaire SA), Pathfile 19.02 (Dentsply Maillefer, Ballaigues, Switzerland), Proglider 16.02 (Dentsply Maillefer, Ballaigues, Switzerland), and Hyflex GPS 20.02 (Coltène Whaledent, Allstätten, Switzerland). The instruments were subjected to cyclic fatigue testing using simulated canals with a 6mm radius and 30° or 45° curvature angles. The data obtained were organized in an Excel spreadsheet and analyzed statistically using BioEstat 5.3 software (Marimauá Institute, Manaus, Brazil). The non-parametric Kruskal-Wallis test was used in the analysis. The Mann-Whitney U-test was used for multiple comparisons, at a significance level of 5%.

Results: The Hyflex instrument was superior to all the other instruments (p<0.05), and Pathfile had a superior fatigue time (p<0.05) compared with Scout Race and Proglider, for both of the curvature angles analyzed. No significant difference was observed between Scout Race and Proglider.

Conclusions: Cyclic fatigue resistance of the HyFlex GPF instrument was the highest among those tested, and the curvature radius had a significant effect on fatigue resistance. A significant decrease in the cyclic fatigue time was observed, with an increase in the flexion (curvature angle), irrespective of the instrument analyzed.