Influence of Artificial Canal Lubricants on the Lifespan of One Curve File under Static and Dynamic Test Modes

Abstract

Aim: This study was designed to determine the lifespan of One Curve (OC) heat-treated nickel-titanium (NiTi) rotary files operating understatic and dynamic fatigue conditions using intracanal lubricants such as oil or sodium hypochlorite (NaOCl). Materials and Methods: The OC files were tested using an artificial zirconia canal. They were tested in air without any intracanal lubricant under static (Group 1) and dynamic (Group 4) modes, and after filling the canal with either oil (Group 2 and Group 5 under static and dynamic modes respectively) or 1% NaOCl (Group 3 and Group 6 under static and dynamic modes respectively). One Curve files were rotated freely in the canal at a speed of 350 rpm (continuous clockwise) under static mode until file failure occurred through fracture. In case of dynamic testing, the instruments were rotated at the same conditions in the canal, but with an additional back and forth movement until fracturing. The number of cycles to fracture (NCF) was recorded and statistically analyzed using One Way ANOVA and Bonferroni tests. Results: Testing of the file in air demonstrated the lowest fatigue resistance, where the static test mode (NCF: 560 ± 8.25) was the worse than the dynamic mode (NCF: 636.81±14.49). On the other hand, the instruments tested under both static and dynamic modes in oil as an intracanal lubricant showed improved lifespan in terms of NCF (1193.89±7.96 and 1351.39 ± 7.06) compared to the same modes in NaOCl lubrication (878.89 ± 8.59 and 1093.82±39.08). Regardless of intracanal lubricant, the dynamic groups produced better results than the static ones. In terms of fractured length, significant differences were identified between the groups except between Group 2 and Group 6. Conclusions: Type of intracanal lubricant demonstrated a more influential effect on the file lifespan than the mode of cyclic fatigue (CF) test. The dynamic CF test utilizing oil intracanal lubricant resulted the best improvement in the file lifespan.