Comparative evaluation of fracture resistance of Hyflex EDM OGSF file system, Protaper Ultimate and RACE EVO file system: an in vitro study

INTRODUCTION. The intracanal fracture of nickel-titanium (NiTi) rotary instruments remains a significant procedural concern in endodontics. Advances in metallurgy, manufacturing processes, and geometric design have led to the development of new file systems with enhanced mechanical properties. The Hyflex EDM OGSF (HEDM), Protaper Ultimate (PTU), and RACE EVO (RE) systems represent distinct technological approaches to improving instrument safety. However, a direct comparative evaluation of their fracture resistance is limited. MATERIALS AND METHODS. A total of 120 new NiTi files, 40 from each system (HEDM, PTU, RE), with a tip size of 25 and a .07 taper, were selected. For the cyclic fatigue test (n = 20 per group), instruments were rotated in a custom-fabricated stainless steel artificial canal with a 60° angle of curvature and a 5 mm radius until fracture. The number of cycles to fracture (NCF) was calculated. For the torsional resistance test (n = 20 per group), the apical 3 mm of each file was clamped, and the instrument was rotated clockwise at 2 RPM until fracture, following ISO 3630-1 standards. Maximum torque (Ncm) and angular deflection (degrees) at failure were recorded. Data were statistically analyzed using one-way ANOVA and Tukey’s HSD post-hoc test (α = 0.05). RESULTS. HEDM exhibited a significantly higher mean NCF (852.5 ± 75.3) compared to both RE (621.8 ± 60.2) and PTU (455.1 ± 55.4) ( p < 0.001). RE also showed significantly higher cyclic fatigue resistance than PTU ( p < 0.001). In the torsional test, PTU demonstrated the highest maximum torque to fracture (0.46 ± 0.05 Ncm), which was significantly greater than RE (0.41 ± 0.04 Ncm) and HEDM (0.34 ± 0.06 Ncm) ( p < 0.001). The difference in torque resistance between RE and HEDM was also statistically significant ( p < 0.01). CONCLUSIONS. Within the limitations of this laboratory study, the Hyflex EDM OGSF file system demonstrated the highest resistance to cyclic fatigue. The Protaper Ultimate file system exhibited the greatest resistance to torsional fracture. The choice of instrument should be guided by the specific anatomical challenges of the root canal system.