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 nickeltitanium instruments -Reciproc blue (RB) and One Curve (OC)- used for single or in a certain number of times.Material and Method: One Curve (n=40) and Reciproc Blue (n=40) files were used in this study. The instruments were dividedinto two subgroups (n=20); those to be used for the first time (N) and those that were previously used (U) only once in the clinicfor the root canal treatment of one vital mandibular molar with three root canals. Cyclic fatigue testing of these instrumentswas performed in an artificial stainless-steel canal with 60° curvature, 5 mm radius 1.5 mm width, and 3.0 mm depth. All thetested files were rotated/reciprocated under the continuous irrigation with distilled water at 37°C until fracture occurred. Thetime to failure (TTF) in seconds and the number of cycles to failure (NCF) were recorded. Data were statistically analyzed andthe 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 RBand OC instruments significantly reduced the cyclic fatigue resistance of the instrument.