An Investigation of the Torsional Force to Fracture of Vortex Nickel-Titanium Rotary Files

Hypothesis: The null hypothesis is that there is no significant difference in the torsional force (TFF) and angle of rotation to fracture between Vortex® Nickel-Titanium (V-NiTi) and Vortex® Blue™ Nickel-Titanium (VB-NiTi) endodontic rotary files after 1 and 3 clinically simulated uses. Objective: The purpose of this in vitro study is to compare the TFF and angle of rotation to fracture of V-NiTi versus VB-NiTi endodontic rotary files after 1 and 3 clinically simulated uses. Methods: One hundred sixty simulated root canals (30-degree curvature) in clear resin blocks (Endo-training bloc A0177, DENTSPLY Maillefer, Ballaigues, Switzerland) were used for this study. NiTi instruments sizes 20, 25 and 30 at 25mm length with 4% and 6% taper were compared (n=10 per test group). The measurements of TFF and angle of rotation to fracture were recorded with a torsiometer instrument (Sabri Dental Enterprises, Inc, Downers Grove, IL). TFF was evaluated by measuring the torque in gram-centimeters (g-cm) and angle of deflection (degrees of rotation) required for instrument separation using a torsiometer after 1 and 3-simulated clinical usages. Peak torque (gm-cm) and angle of rotation (degree) of NiTi files tested were analyzed using ANOVA and Tukey’s Post Hoc test. Results: The results of this study demonstrated VB-NiTi files had a statistically significant (p<0.05) higher TFF value and angle of rotation to fracture after 1 and 3 uses as compared to V-NiTi files. There was also a significant (p<0.05) difference in TFF values and angle of rotation to fracture between 1 and 3 uses for within each file system. Conclusions: We reject the null hypothesis. Higher torque to failure values and angle of rotation of VB-NiTi files as compared to V-NiTi files correlates to the increased flexibility of the proprietary M-wire metal used in the manufacturing of VB-NiTi files.