Comparison of the cyclic fatigue resistance of original, replica-like and counterfeit nickel-ti̇tanium files operating in reciprocating motion: N vitro study

Aim: The aim of this study is to compare the design features, cyclic fatigue resistance at body temperature, and metallurgical properties of original, replica-like, and counterfeit nickel-titanium files operating in reciprocating motion. Materials and Methods: A total of 100 nickel-titanium files, comprising four groups of original (Reciproc Blue R25), replica-like (Recip-One Files Blue R25), and counterfeit (Reciproc Blue R25) systems, were used in this study. To evaluate the design features of the files, manufacturing defects were compared using a stereomicroscope; tip designs were examined through data obtained from scanning electron microscopy (SEM), and taper and tip diameter values were measured and compared using the ImageJ software. The accuracy of the 18-20 mm measurement lines was assessed using a digital caliper. The cyclic fatigue test was conducted at body temperature (37°C) in an artificial canal with a 60° curvature angle and a 5 mm curvature radius. The metallurgical properties of the samples were analyzed via differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (SEM-EDS). The normality of the data was assessed using the Shapiro-Wilk test. For normally distributed data, a one-way ANOVA was performed, and for non-normally distributed data, the Kruskal-Wallis test was used. Post hoc analysis was conducted using the Games-Howell and Bonferroni tests. The significance level was set at 5%. Results: The counterfeit file systems (Cf1, Cf2) were distinguishable from the other groups through the observation of manufacturing defects under a stereomicroscope. While the original file system (Of) and the replica-like file system (Rf) exhibited passive tip designs, the counterfeit file systems showed active tip designs under SEM analysis. The Rf group files demonstrated similar tip diameter and taper values to the Of group, whereas the Cf1 group files displayed lower taper and tip diameter values compared to the Of group. The counterfeit file systems exhibited deviations of over 0.1 mm from the measurement lines compared to the other groups. The cyclic fatigue test results indicated that the fracture times were similar across the groups. DSC results revealed that the Of group files were in the austenite phase at body temperature, while the other group files remained in the martensitic phase. According to SEM-EDS analysis, the nickel-titanium ratios were similar across all groups. Conclusion: In this study, which compared original, replica-like, and counterfeit file systems, similarities were observed in cyclic fatigue resistance and nickel-titanium levels among the groups, while differences were noted in design features and DSC results. The counterfeit file systems did not meet the claimed taper and tip diameter values, and the data examined showed that the standard deviation values of these systems were higher compared to the other groups. It can be concluded that these non-standardized systems are not as reliable as the original systems.