Effect of usage and autoclaving on the cyclic fatigue resistance of heat-treated nickel-titanium instrument

Abstract

Background: Nickel-titanium (NiTi) instruments are often reused in endodontic treatment for economic reasons. Thus, cleaning, disinfection, and sterilization of these endodontic instruments are essential. Several studies have shown that additional heat treatment during the sterilization of NiTi instruments affects their physical properties. Some researchers concluded that sterilization has a detrimental impact on the physical properties of NiTi files. However, others found that sterilization for up to 10 cycles does not increase the risk of NiTi failure.

Aim: To evaluate the effect of usage and sterilization on the cyclic fatigue resistance of a heat-treated NiTi instrument (ProTaper Gold).

Materials and Methods: Thirty ProTaper Gold NiTi F2 files (length 25 mm) were used in this study. The files were assigned to three groups: Group I, new files (control group); Group II, files that underwent autoclave sterilization at 134 °C for 30 mins; and Group III, files that were prepared in a standardized J-shaped endo block followed by autoclave sterilization. Each NiTi file was rotated in an artificial curved metal block using a custom-made device in a repetitive up and down motion in a dynamic mode until fracture occur. The duration taken for the fracture to occur was recorded and translated into a number of cycles to failure (NCF). A digital micro-caliper was used to measure the length of the broken fragment. Following the cyclic fatigue test, all fractured fragments were examined under a scanning electron microscope to determine the topographic characteristics of the damaged surfaces. The data was analyzed using SPSS. The NCF was compared across the three groups using ANOVA, and fragment length using the Kruskal-Wallis test. A p-value of 0.05, was considered significant in all experiments.

Results: There was no statistically significant difference in the number of cycles to failure (NCF) among the three classes (P = 0.292.). Scanning electron microscopy revealed the typical features of cyclic fatigue failure of each fracture surface.

Conclusion: Under the limitations of this analysis, the findings provide precursory evidence that single canal file use and a single autoclave sterilization cycle do not affect the cyclic fatigue resistance of heat-treated nickel-titanium endodontic instrument (ProTaper Gold).