Impact of Autoclaving on the Mechanical Performance and Metallurgical Behavior of ProTaper Ultimate, BlueShaper, and...

This study assessed the effect of autoclaving on the mechanical properties and metallurgy of heat-treated nickel-titanium rotary files.

Files from ProTaper Ultimate (PTU), BlueShaper (BSH), and ZenFlex (ZFL) systems (n = 60) were divided into 3 groups based on autoclaving cycles (0, 3, and 7) (n = 20). In each group, the files were tested under torsional stress or dynamic cyclic fatigue (n = 10 each). The fractured fragments from both tests were examined using scanning electron microscopy. New files from each system were subjected to 0, 3, and 7 autoclaving cycles and tested using energy-dispersive spectroscopy and differential scanning calorimetry. Data were analyzed using two-way ANOVA and Wilcoxon signed-rank test at a 5% significance level.

BSH exhibited the highest torsional strength and dynamic cyclic fatigue resistance, particularly after 3 and 7 autoclaving cycles, followed by PTU and ZFL. ZFL showed a higher distortion angle than PTU and BSH after 3 and 7 cycles. Autoclaving decreased torsional strength of BSH and increased the distortion angle of ZFL. BSH exhibited the highest austenite finish and martensite start temperatures, with minimal thermal degradation observed after autoclaving.

BSH demonstrated the highest torsional strength, dynamic cyclic fatigue resistance, and phase transformation temperatures across all autoclaving cycles, followed by PTU and ZFL. Autoclaving reduced torsional strength of BSH and increased distortion angle of ZFL but did not affect the dynamic cyclic fatigue resistance, phase transformation, or elemental analysis of the other tested files.