A Comparative Evaluation of the Cyclic Fatigue Resistance of Three Nickel-Titanium Rotary File Systems in a Simulated Curved Canal: An In Vitro Study

Introduction: Nickel-titanium (NiTi) rotary instruments have significantly improved the efficiency and predictability of root canal preparation because of their superior flexibility and shape-memory characteristics. Despite these advantages, unexpected instrument separation caused by cyclic fatigue remains a major clinical concern, particularly during instrumentation of curved root canals. Continuous advancements in heat treatment and instrument design have led to the introduction of newer rotary systems with improved mechanical properties. However, comparative evidence regarding their cyclic fatigue resistance remains limited. This study aimed to compare the cyclic fatigue resistance of three NiTi rotary file systems in a standardized simulated curved canal under in vitro conditions. Methods: An in vitro study was conducted using 60 new NiTi rotary files equally allocated into three groups (n = 20): GenEndo, Orodeka Plex, and ProTaper Gold. All instruments were tested in a custom-fabricated stainless steel artificial canal with a standardized curvature under continuous rotation using manufacturer-recommended speed and torque settings. The time to fracture was recorded using a digital stopwatch, and the number of cycles to fracture (NCF) was calculated. Representative fractured specimens were qualitatively examined using scanning electron microscopy (SEM). Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey's post hoc test, with statistical significance set at p < 0.05. Results: ProTaper Gold demonstrated the longest mean time to fracture (806.80 ± 58.65 seconds), followed by Orodeka Plex (514.65 ± 51.56 seconds) and GenEndo (406.80 ± 66.02 seconds). Orodeka Plex exhibited the highest mean NCF (4153.25 ± 421.74), followed by ProTaper Gold (3962.40 ± 297.80) and GenEndo (2619.20 ± 437.56). One-way ANOVA revealed statistically significant differences among the three rotary systems for both the time to fracture and NCF (p < 0.001). Post hoc analysis demonstrated significant pairwise differences in time to fracture among all groups, whereas Orodeka Plex and ProTaper Gold showed comparable NCF values (p = 0.278). SEM examination revealed characteristic cyclic fatigue fracture features, including crack initiation zones, fatigue striations, and overload regions, in all tested instruments. Conclusion: The tested rotary file systems exhibited significantly different cyclic fatigue behaviors under standardized laboratory conditions. ProTaper Gold demonstrated the greatest resistance in terms of fracture time, whereas Orodeka Plex achieved the highest NCF. GenEndo showed a comparatively lower fatigue resistance. Instrument metallurgy, heat treatment, rotational speed, and geometric design appear to play important roles in determining the fatigue performance of NiTi rotary instruments.