Comparison of cyclic fatigue resistance of used and new RaCe instruments.

Objective: The aim of this study was to evaluate cyclic fatigue resistance of used and new RaCe rotary nickel-titanium instruments.

Study Design: Forty RaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) instruments of sizes 30/.06, 30/.02, 25/.04, and 25/.02 were selected and divided into 2 groups: group A = 20 new instruments; group B = 20 used instruments. In group B, each instrument was used for shaping 5 curved molar root canals. Cyclic fatigue testing of new and used instruments was performed using a device that allowed the instruments to rotate freely inside a stainless steel artificial canal. Data were analyzed using t test to determine any statistical significance between used and new instruments of the same file size.

Results: For all sizes, new instruments were more resistant to failure then the used ones (P < .05). A reduction in lifespan was observed ranging from 18% (30/.06) to 51% (25/.02).

Conclusion: The results showed that clinical use significantly reduced cyclic fatigue resistance of RaCe rotary instruments compared with new ones.