Comparison of Design, Cyclic Fatigue Resistance, and Metallurgical Properties of Original, Replica-Like, and Counterfeit Nickel-Titanium Files.

Abstract

This study aimed to compare the design characteristics, cyclic fatigue resistance, and metallurgical properties of original, replica-like, and counterfeit nickel-titanium systems. One hundred Ni-Ti files were evaluated and categorized into four groups: the original (Of-Reciproc Blue R25) system, a replica-like (Rf-Recip-One Files Blue R25) system, and two counterfeit (Cf1, Cf2) systems. The design characteristics were assessed based on packaging features, manufacturing defects observed using a stereomicroscope, tip design analyzed via scanning electron microscopy (SEM), and taper and tip diameter measurements conducted with Image J software (National Institutes of Health, Bethesda, MD, USA). Cyclic fatigue testing was performed at body temperature in an artificial canal with a 60° angle of curvature and a 5 mm radius of curvature. Metallurgical properties were examined using differential scanning calorimetry (DSC) and energy-dispersive spectroscopy (SEM-EDS). Statistical analysis was conducted using the Kruskal-Wallis test with post hoc Dunn-Bonferroni tests, with the significance level set at 5%. The Cf systems were distinguished from the Of system by the observation of manufacturing defects under a stereomicroscope. While the Of and Rf systems exhibited passive tip designs, the Cf systems displayed active tip designs. The Rf system showed tip diameter and taper values similar to those of the Of system, whereas the Cf1 system demonstrated lower tip diameter and taper values compared to the Of system. Cyclic fatigue test results revealed no statistically significant difference in fracture times between the systems. DSC analysis indicated that the Of system was in the austenite phase at body temperature, while the other systems were in the martensite phase. SEM-EDS analysis revealed similar nickel-titanium compositions across all systems. The Rf system showed similar design, mechanical, and metallurgical properties to the Of system, while Cf systems lacked consistency in standardization and design. The presence of manufacturing defects, along with discrepancies in claimed design specifications such as tip diameter and taper, and the fact that counterfeit systems exist in a different metallurgical phase compared to the original system, may predispose clinicians to potential complications during clinical use.