Stationary Fatigue Resistance of Various Rotary Instruments with Different Alloys after Preparing Three Root Canals

OBJECTIVE: This study aimed to evaluate the stationary fatigue resistance of three endodontic instrument systems after preparing three root canals with different curvatures and comparing them with unused instruments. METHODS: A total of 60 endodontic files from 3 instrument systems, TruNatomy (TRN), HyFlex CM (HFC) and Revo-S (RS), were selected for this study. These systems were divided into 2 groups: Group I (Used files) and Group II (Unused files). Each group was further divided into 3 subgroups, each containing 10 TRN (#26/v.04), 10 HFC (#25.04) and 10 RS (#25/.04) rotary files. The group I instruments were used for shaping the root canals of extracted third molars, while the group II instruments were not used for canal shaping procedures. Both Group I and Group II instruments were subjected to stationary cyclic fatigue testing at simulated body temperature (37±0.5°C) using a stainless-steel block with an artificial canal. The number of cycles to failure (NCF), the length of fractured instruments and the preparation time were recorded. The statistical analysis was performed using two-way ANOVA and Tukey post-hoc tests with a 95% confidence interval (P=0.05). RESULTS: NCF was significantly affected by the instrument type and whether the instrument was unused or used (P<0.001). The Group II instruments were more resistant to stationary cyclic fatigue than Group I (P<0.05). HFC instruments were most resistant to stationary fatigue among all tested conditions, followed by TRN and RS instruments. Canal preparation with TRN was significantly faster than with HFC and RS. During preparation, no file was fractured. A statistically significant difference (P<0.05) was observed in the mean length of the fractured instruments among used instrument groups. CONCLUSION: The stationary cyclic fatigue resistance of HFC instruments were significantly greater than that of the TRN and RS instruments (P<0.05). TRN was faster in shaping the root canals than other instruments tested in the study.