Influence of clinical use on fatigue resistance of ProFile instruments

Objectives:evaluates the influence of clinical use of rotary NiTi ProFile instruments on the deterioration of their fatigue life. Methods:A total of 150 new instruments, taper .04 and .06, sizes 20, 25 and 30, were divided into two groups: Control Group (CG), consisting of 60 instruments fatigue tested until rupture, in order to establish the average number of cycles to failure (NCF); Experimental Group (EG), with 90 instruments employed in formatting 10 curved canals of molars, and tested in the fatigue bench to evaluate the change in their fatigue life. Results:The instruments of CG and EG showed average values of NCF varying from 950 to 770 and from 443 to 287, respectively, the smaller size instruments achieving the highest values of NCF.The results concerning the position of fracture indicated that instruments separation always took place at the region of maximum strain amplitude, located at approximately 3.1mm from the tip of the instrument, as established by the geometry of the artificial canal employed in the test bench. Conclusions:A significant reduction in the NCF of the clinically used instruments, in relation to the new instruments, was observed, demonstrating that the clinical use decreased their fatigue resistance.This reduction varied from instrument to instrument and, considering the average values of NCF in the CG and EG, the remaining fatigue life can be estimated as 46.6, 49. 0, 39.2, 42.9, 38.0 e 37.3%, for the instruments 20/.04, 25/.04, 30/.04, 20/.06, 25/.06 e 30/.06, respectively.