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

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.

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).

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.

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.