Mechanical and elemental comparison of EndoStar and One Curve nickel-titanium endodontic files: An in vitro study.

OBJECTIVE: To compare the cyclic fatigue resistance, bending behavior, and elemental composition of two heat-treated nickel-titanium (NiTi) rotary file systems, Endostar E3 Azure and One Curve, using standardized in vitro mechanical and surface characterization protocols. METHODOLOGY: The study randomly allocated 90 new size 25/0.06 NiTi rotary files (n = 45 Endostar; n = 45 One Curve) into three subgroups (n = 15 each) for dynamic cyclic fatigue testing, bending resistance assessment, and scanning electron microscopy/EDS analysis. Fatigue testing was performed in a dynamic stainless-steel canal at 37°C ± 1°C using a pecking motion. Bending resistance was measured according to ISO 3630-1 using a universal testing machine. Elemental composition was analyzed with energy-dispersive X-ray spectroscopy. Statistical comparisons were made using independent-samples t-tests (P < 0.05). RESULTS: Endostar exhibited significantly greater cyclic fatigue resistance compared with One Curve, showing higher number of cycles to fracture (2814.3 ± 488.9 vs. 1454.7 ± 452.5; P < 0.001) and longer time to fracture (567.1 ± 102.6 s vs. 288.5 ± 92.4 s; P < 0.001). Bending resistance was higher in Endostar (852.8 ± 36.6 gf) compared with One Curve (538.8 ± 57.1 gf; P < 0.001). EDS analysis revealed increased oxygen levels in Endostar and higher nickel and carbon levels in One Curve. CONCLUSION: Endostar E3 Azure demonstrated superior cyclic fatigue resistance, higher bending stiffness, and distinct surface chemistry compared with One Curve. Surface elemental variations and heat-treated differences may be associated with the observed mechanical variations; however, mechanistic interpretation requires further phase-transformation analysis.