The Effects of Autoclave Sterilization on the Cyclic Fatigue Resistance of Various Heat-Treated Nickel-Titanium Instruments Under Varied Kinematic Conditions

Abstract

This study aimed to evaluate and compare the effects of autoclave sterilization on static and dynamic cyclic fatigue tests of various heat-treated Ni-Ti instruments in single artificial stainless-steel canals. Three brands of heat-treated Ni-Ti rotary instruments were used for this study: TruNatomy (TRN; prime, 26/.04 taper), WaveOne Gold (WOG; primary, 25/.07 taper), and ProTaper Gold (PTG; F2, 25/.08 taper). All files used in this study were 25 mm long. A total of 144 instruments for each system were divided into two groups (n = 72 each) according to the cyclic fatigue testing modes (static mode and dynamic mode). Each group was subdivided into three subgroups (n = 24 each) according to sterilization condition (no-sterilization [NSC], five-cycle-sterilization [5SC], and ten-cycle- sterilization [10SC] subgroups). All the static and dynamic cyclic fatigue resistance tests were performed in two customized devices (AendoS; DMJ System, Busan, Korea). In static mode, there were no statistically significant differences in the mean numbers of cycles to fracture (NCFs) between the three subgroups with either WOG or TRN. However, with PTG, there were significant differences between the mean NCFs of the sterilization-condition subgroups. In dynamic mode with WOG, there were no statistically significant differences between the mean NCFs of the three subgroups. However, there was a significant difference between the mean NCFs of the NSC and 10SC subgroups with TRN and PTG. Between TRN, WOG, and PTG, there were no significant differences in mean file fragment length, regardless of sterilization condition, in both static and dynamic modes. The study findings revealed that, compared with static mode, cyclic fatigue resistance was significantly higher in dynamic mode for all investigated Ni-Ti instrument systems. Within the limitations of this study, it can be concluded PTG autoclaved ten times had higher cyclic fatigue resistance than unsterilized instruments in tests conducted in both static and dynamic modes. However, TRN autoclaved ten times had lower cyclic fatigue resistance than unsterilized instruments. With WOG, there were no significant differences between any of the sterilization-condition subgroups in either static or dynamic mode.