Mechanical Performance and Metallurgical Characteristics of 5 Different Single-file Reciprocating Instruments: A Comparative In Vitro and Laboratory Study.

INTRODUCTION: Because there are no data regarding an instrument recently introduced on the market (OneRECI; Coltene MicroMega, Besançon, France), the aim of this study was to assess its mechanical and metallurgical properties comparing them with the following widespread reciprocating instruments: Reciproc (VDW, Munich, Germany), Reciproc Blue (VDW), EdgeOne Fire (EdgeEndo, Albuquerque, NM), and WaveOne Gold (Dentsply Maillefer, Ballaigues, Switzerland). METHODS: A total of 65 nickel-titanium files from 5 different reciprocating systems (OneRECI, Reciproc, Reciproc Blue, EdgeOne Fire, and WaveOne Gold) were evaluated throughout a combined mechanical and metallurgical method. Mechanical performances of the selected file were examined by subjecting each specimen to cyclic fatigue and torsional and bending resistance tests, whereas their metallurgical properties were assessed by analyzing the nickel-titanium alloy composition and the phase transformation temperatures through energy-dispersive X-ray spectroscopy and differential scanning calorimetry, respectively. One-way analysis of variance and the post hoc Tukey test were performed with the significance level set to a 95% confidence level. RESULTS: Energy-dispersive X-ray spectroscopy showed a similar alloy composition for all of the tested files, with a nickel percentage of about 52%-53% and a corresponding percentage of titanium of 47%-48%, whereas the differential scanning calorimetry analysis, although it indicated martensitic characteristics for all files, showed differences in terms of phase transformation temperatures. Overall, OneRECI showed the best mechanical performances in terms of cyclic fatigue and torsional resistance (32.95 ± 2.33 seconds and 0.76 ± 0.03 Ncm, respectively) and flexibility (48.4 ± 4.1 g), with statistically significant differences for all tests (P < .05). The Reciproc files showed the worst flexibility and cyclic fatigue resistance (157.2 ± 8.3 g and 9.27 ± 1.18 seconds, respectively), whereas the EdgeOne Fire showed the lowest torsional resistance (0.39 ± 0.12 Ncm), with statistically significant differences (P < .05). CONCLUSIONS: Within the limitations of this study, the recently introduced OneRECI file showed the best mechanical performance in comparison to the tested instruments, with an equiatomic composition of the nickel-titanium alloy and a martensitic behavior.

Cyclic fatigue resistance, torsional resistance, and metallurgical characteristics of M3 Rotary and M3 Pro Gold NiTi files

OBJECTIVES: To evaluate the mechanical properties and metallurgical characteristics of the M3 Rotary and M3 Pro Gold files (United Dental). MATERIALS AND METHODS: One hundred and sixty new M3 Rotary and M3 Pro Gold files (sizes 20/0.04 and 25/0.04) were used. Torque and angle of rotation at failure (n = 20) were measured according to ISO 3630-1. Cyclic fatigue resistance was tested by measuring the number of cycles to failure in an artificial stainless steel canal (60° angle of curvature and a 5-mm radius). The metallurgical characteristics were investigated by differential scanning calorimetry. Data were analyzed using analysis of variance and the Student-Newman-Keuls test. RESULTS: Comparing the same size of the 2 different instruments, cyclic fatigue resistance was significantly higher in the M3 Pro Gold files than in the M3 Rotary files (p < 0.001). No significant difference was observed between the files in the maximum torque load, while a significantly higher angular rotation to fracture was observed for M3 Pro Gold (p < 0.05). In the DSC analysis, the M3 Pro Gold files showed one prominent peak on the heating curve and 2 prominent peaks on the cooling curve. In contrast, the M3 Rotary files showed 1 small peak on the heating curve and 1 small peak on the cooling curve. CONCLUSIONS: The M3 Pro Gold files showed greater flexibility and angular rotation than the M3 Rotary files, without decrement of their torque resistance. The superior flexibility of M3 Pro Gold files can be attributed to their martensite phase.