Comparison between a Novel Nickel-Titanium Alloy And 508 Nitinol on Cyclic Fatigue Life of ProFile 25/.04 Rotary Instruments

Signature Grand, Davie, Florida, USA

Objective. To test the cyclic fatigue resistance of nickel-titanium rotary files produced from 508 Nitinol and M-Wire™ NiTi alloys. Background. Endodontic files must resist breakage, and this is measured as cyclic fatigue. Methods. Thirty ProFile® 25/.04 instruments were manufactured from one of three variants of 508 Nitinol that were subjected to different thermo-mechanical processing. Controls (n = 30 each) consisted of stock 508 Nitinol 25/.04, as well as 25/.02 and 25/.06 instruments. Investigation of the cyclic fatigue was performed by rotating instruments at 300 RPM in a simulated steel root canal with a 90º curve of 5 mm radius until separation occurred. The number of rotations to failure was calculated. Torsion testing at failure was also undertaken by clamping 3 mm of the tip of each instrument between brass plates and rotating it at 2 RPM until failure. Data were recorded for torque and angle at fracture of thirty instruments per group. Results. Cyclic fatigue of different alloys was analyzed using Welch’s ANOVA. Dunnett’s T3 test was used for all pair-wise comparisons. Statistical differences were found with an M-Wire™ NiTi variant nearly 400% more resistant to cyclic fatigue than stock 508 Nitinol (p < .001). Load to fracture was analyzed using an ANCOVA model, with Tukey’s-HSD test applied to all pair-wise comparisons. Significant differences were found between all 508 Nitinol groups and M-Wire™ NiTi (p < 0.001). Conclusion. ProFile 25/.04 files manufactured from M-Wire NiTi have significantly greater resistance to cyclic fatigue while maintaining comparable torsional properties.