Cyclic fatigue of Profile rotary instruments after prolonged clinical use

Aim The purpose of the present study was to evaluate resistance to cyclic f atigue of new and used Profile Ni-Ti rotary instruments. Methodology Used instruments were operated in 10 clinical cases using passi ve instrumentation and a crown-down preparation technique. Cyclic fatigue t esting of new and used engine-driven instruments was then performed with a specific device which allowed the instruments to rotate freely inside a sta inless steel artificial canal, whilst maintaining conditions close to the c linical situation. Instruments were rotated until fracture occurred and tim e to fracture was visually recorded with a chronometer. Results A significant reduction of rotation time to breakage (life span) wa s 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 signi ficantly reduced their cyclic fatigue resistance. Nevertheless, each rotary instrument was successfully operated in up to 10 clinical cases without an y intracanal failure.