Comparison between Single-file Rotary Systems: Part 2-The Effect of Length of the Instrument Subjected to Cyclic Loading on Cyclic Fatigue Resistance.

INTRODUCTION

The aim of this study was to compare the cyclic fatigue resistance of XP Shaper (XP), HyFlex EDM One File (EDM), and WaveOne Gold Primary (WOG) when operated according to their manufacturers' recommendations at different lengths and to investigate the cyclic fatigue limit of XP Shaper when operated at 3000 rpm.

METHODS

One hundred fifty instruments from 4 different rotary systems (F2 Protaper Universal [PTU], WOG, EDM, and XP) were tested for their cyclic fatigue resistance in a simulated 90° curved canal at a 37°C water bath temperature at 3 different working lengths (15 mm, 17 mm, and 19 mm). The time taken for instruments to fracture was recorded, and the number of cycles to failure was calculated. Statistical analyses were performed by using Levene's test, Kruskal-Wallis test to identify specific groups with statistically significantly higher cyclic fatigue resistance at 5% significance level. Weibull analysis was performed to determine the predictability of survival for each instrument.

RESULTS

XP Shaper had the highest cyclic fatigue resistance compared with all other instruments, followed by EDM, WOG, and then PTU. There was no statistically significant difference in the number of cycles to failure between the XP operated at 3000 or 1000 rpm in any of the tested working lengths. There was a reduction in the number of cycles to failure when the working length increased from 15 to 19 mm in EDM, WOG, and PTU. Scanning electron microscopy showed ductile fractures with classic dimpled features in all samples.

CONCLUSIONS

XP has a very high resistance to cyclic fatigue compared with WOG, EDM, and F2 PTU. The time to fracture will decrease by almost one third when XP is operated at 3000 rpm. The results of both parts of this study suggest that XP appears to be safe to operate at 3000 rpm in endodontic retreatment.