Comparing the impact of various sterilization methods on the cyclic fatigue resistance, bending strength, and torsional fatigue properties of NiTi rotary files

Abstract This study aimed to evaluate the influence of various sterilization techniques on the cyclic fatigue resistance, bending strength, and torsional fatigue resistance of Tornado Blue and Race Evo rotary endodontic file systems. Both the file systems underwent a series of 15 cycles of sterilization according to the following study groups: control group (G1; i.e., without treatment), chemical sterilization with 5.25% sodium hypochlorite (G2), dry heat sterilization (G3), glass beads sterilization (G4), and steam autoclaving (G5). Each group consisted of 8 samples (n = 8/group). Statistical analysis was performed using a two-way ANOVA and Tukey’s tests (p ≤ 0.05). Mean values for the number of cycles between both files were 1291 ± 52.79 rpm and 2095 ± 52.91 rpm for Tornado Blue and Race Evo, respectively. The torsional fatigue resistance was 8.00 ± 0.85 NCF and 10.70 ± 0.85 NCF and the bending strength was 486.94 ± 20.97 gf and 564.17 ± 20.97 gf for Tornado Blue and Race Evo, respectively. The results showed no significant difference in the mechanical properties followed by different sterilization protocols. However, a significant difference was observed in tested properties between the two file systems (p ≤ 0.05). The outcome is reassuring for clinicians that the essential process of routine sterilization at clinics seems safe with regards to mechanical integrity of the endodontic files.