Comparison of design, metallurgy, mechanical performance and shaping ability of replica-like and counterfeit instruments of the ProTaper Next system.

AIM To compare the ProTaper Next (PTN) system with a replica-like and a counterfeit system regarding design, metallurgy, mechanical performance and shaping ability. METHODOLOGY Replica-like (X-File) and counterfeit (PTN-CF) instruments were compared to the PTN system regarding design (microscopy), phase transformation temperatures (differential scanning calorimetry), nickel-titanium ratio (energy-dispersive X-ray spectroscopy), cyclic fatigue, torsional and bending strength, and untouched canal areas in extracted mandibular molars (micro-CT). ANOVA post hoc Tukey and Kruskal-Wallis tests were used according to normality assessment (Shapiro-Wilk test) with significance level set at 5%. RESULTS Overall similarities in design and nickel-titanium (Ni/Ti) ratio were observed among instruments with the X-File having a smoother surface finish. PTN and PTN-CF had mixed austenite plus R-phase (R-phase start approximately at 45 oC and near 30 oC, respectively), while X-File instruments were austenitic (R-phase started at approximately at 17 oC) at room temperature (20 oC). PTN-CF had the highest inconsistency in the phase transformation temperatures. Time to fracture of PTN-CF X2 and X3 was lower than PTN and X-File instruments (P 0.05). X-Files and PTN-CF had a stress-induced phase change during bending load. Mean unprepared surface areas of root canals were 25.8% (PTN), 31.1% (X-File) and 32.5% (PTN-CF) with no significant difference among groups (P >0.05). CONCLUSION Similarities amongst the systems were noted in the Ni/Ti ratio and maximum torque to fracture, while differences were observed in the design, phase transformation temperatures and mechanical behaviour. The ProTaper Next counterfeit instruments could be considered as the less secure system considering its low cyclic fatigue resistance. Apart from these differences, the unprepared canal surface areas, obtained with the tested systems, was similar.