Influence of file motion on cyclic fatigue of new nickel titanium instruments.

The aim of the present study was to compare the resistance to cyclic fatigue of Hyflex® (Coltene-Whaledent, Allstatten, Switzerland) size 40 taper.04 nickel titanium instruments used in continuous rotation versus the use with a reciprocating motion. The null hypothesis was that different file motions had no influence on the lifetime of instruments subjected to a cyclic fatigue test. 24 Hyflex® size 40 taper.04 nickel titanium instruments were randomly divided in two groups (n=12 each), and submitted to a cyclic fatigue test. The first group (CR group) were used with a continuous rotation, while the second one (RCP group) with a reciprocating motion. The cyclic fatigue tests were performed by using a stainless steel block containing an artificial canal shaped with a 135° angle. All instruments were rotated or reciprocated until fracture occurred. The time to fracture was recorded visually with a 1/100 second chronometer. Data were recorded and statistically analysed. Results indicated that instruments used with a reciprocating motion showed a significant increase in the meantime to failure when compared to those used in continuous rotation. The null hypothesis was rejected. Results of the present study showed that reciprocating motion extended resistance to cyclic fatigue of the tested nickel titanium instruments, when compared to continuous rotation.