The impact of different autoclaving cycles on the properties of rotary endodontic files

Abstract Background Whether autoclaving affects mechanical and surface characteristics of nickel–titanium rotary instruments is a subject of debate. The present in vitro investigation aimed to determine how autoclaving influences cyclic fatigue resistance and surface roughness of three NiTi rotary files — ProTaper Ultimate (PTU), TruNatomy (TN), and ProTaper Next (PTN), and to assess post-instrumentation root canal dentine roughness. Methods A total of 180 rotary files were allocated into 3 groups ( n = 60) based on file type, and each group was further divided into three subgroups ( n = 20) depending on the number of autoclaving cycles applied (0, 5, and 10). Following sterilization, 10 files per subgroup underwent cyclic fatigue testing in a custom-fabricated apparatus with artificial canals. The remaining 10 files were subjected to surface roughness evaluation via optical profilometry. To assess post-instrumentation dentine roughness, 90 lower premolars were prepared, sectioned longitudinally, and examined using scanning electron microscopy (SEM). SEM micrographs were processed through image-analysis software for roughness quantification. Statistical comparisons were performed using two-way and three-way ANOVA at α = 0.05. Results Cyclic fatigue resistance of TN declined significantly after exposure to 5 and 10 autoclaving cycles, whereas PTU and PTN demonstrated resistance to such changes. Among the three systems, TN recorded the highest cyclic fatigue resistance, followed by PTU and PTN. Surface roughness increased significantly only for TN with progressive autoclavingwhile it increased for PTU and PTN only after exposure to 10 and 5 cycles, respectively. At zero autoclaving cycles, TN exhibited the least roughness, with no statistically significant differences between PTU and PTN. After 5 and 10 cycles, PTN showed the highest roughness, which differed significantly from the other file systems. Regarding dentine roughness, autoclaving of PTU caused an increase in roughness in most subgroups, whereas autoclaving of TN increased dentine roughness in apical and coronal thirds after 10 cycles. In contrast, for PTN, dentine roughness significantly decreased in most subgroups after autoclaving. Conclusion The effect of repeated autoclaving in this study was dependent on the file-system type. Clinicians should consider file-specific responses to autoclaving when establishing sterilization and reuse protocols to optimize instrument safety and root canal surface quality.