Effect of number of uses on the cyclic fatigue resistance of single-file rotary instruments

Abstract

Aim: The purpose of this study was to evaluate and compare the cyclic fatigue resistance of two different single file nickel-titanium instruments -Reciproc blue (RB) and One Curve (OC)- used for single or in a certain number of times.
 Material and Methods: One Curve (n=40) and Reciproc Blue (n=40) files were used in this study. The instruments were divided into two subgroups (n=20); those to be used for the first time(N) and those that were previously used (U) in the clinic for the root canal treatment of a vital mandibular molar with three root canals. Cyclic fatigue testing of these instruments was performed in an artificial stainless-steel canal with 60° curvature, 5 mm radius 1.5 mm width, and 3.0 mm depth. All the tested files were rotated/reciprocated under the continuous irrigation with distilled water at 37°C until fracture occurred. The time to failure (TTF) in seconds and the number of cycles to failure (NCF) were recorded. Data were statistically analyzed and the significance level was set at P < 0.05.
 Results: A significant difference was observed among the four groups and between RB-N/RB-U, OC-N/OC-U, RB-N/OC-N, and RB-U/OC-U, regarding TTF and NCF values (P < 0.05). Predicted time for % 99 survival were RB-N >RB-U > OC-N > OC-U. The TTF value of RB is greater than OC in both the new instrument groups and the used instrument groups.
 Conclusions: RB showed higher cyclic fatigue resistance than OC files in both new and used instrument groups. Reuse of RB and OC instruments significantly reduced the cyclic fatigue resistance of the instrument.