Cyclic fatigue of ProFile rotary instruments after prolonged clinical use

AIM: The purpose of the present study was to evaluate resistance to cyclic fatigue of new and used ProFile Ni-Ti rotary instruments. METHODOLOGY: Used instruments were operated in 10 clinical cases using passive instrumentation and a crown-down preparation technique. Cyclic fatigue testing of new and used engine-driven instruments was then performed with a specific device which allowed the instruments to rotate freely inside a stainless steel artificial canal, whilst maintaining conditions close to the clinical situation. Instruments were rotated until fracture occurred and time to fracture was visually recorded with a chronometer. RESULTS: A significant reduction of rotation time to breakage (life span) was noted between new and used instruments. In all sizes new instruments were significantly more resistant than used ones (two-sample t-test, P < 0.01). No instrument underwent intracanal failure during clinical use. CONCLUSIONS: Prolonged clinical use of Ni-Ti engine-driven instruments significantly reduced their cyclic fatigue resistance. Nevertheless, each rotary instrument was successfully operated in up to 10 clinical cases without any intracanal failure.