Influence of simulated clinical use on the torsional behavior of nickel-titanium rotary endodontic instruments

Objective. The aim of this study was to assess the influence of cyclic deformation up to one half and three quarters of the fatigue life of NiTi rotary endodontic instruments on their behavior in torsion. Study design. Thirty sets of 0.04 and 0.06 ProFile instruments in sizes #20, #25, and #30 were randomly divided into 3 groups: I contained 10 sets of new files, torsion tested to failure, while the other 2 groups, with 10 sets each, were first submitted to fatigue tests of up to one half and three fourths of their fatigue life, respectively, in geometrical conditions similar to those of the clinical practice and then torsion tested for rupture. Results. Statistical analysis of the values obtained for the torque to failure and maximum angular deflection, using the Student t test at the 95% confidence level, showed that the cyclic deformation of instruments of up to one half and three fourths of their fatigue life gives rise to a significant reduction in these parameters. Conclusions. The simulated clinical use of ProFile instruments for shaping curved canals adversely affects their torsional properties.