Influência do movimento de pressão lateral na resistência à torção e à fadiga de instrumentos ProTaper Universal

Abstract

The aim of this work was to assess the influence of lateral pressure motion during multiple clinical uses on the torsional and fatigue resistance of NiTi rotary ProTaper Universal endodontic instruments. Twenty sets of new instruments were tested until rupture in a torsion test machine (n = 10) and in a fatigue test device (n = 10), in order to determine the mean values of maximum torque and of number of cycles to failure (NCF), respectively. Forty sets of new instruments were used in the work. Each set was employed to clean and shape 5 molars, twenty sets using lateral pressure (LP) motion with the S1, S2 and SX instruments, while in the other sets no lateral pressure motion (NLP) was applied to these instruments. After that, the clinically used instruments were torsion tested until rupture, to evaluate the consumption of torsional resistance, or fatigue tested to assess their remaining fatigue life. Three sets of each group were observed by scanning electron microscopy before and after being used. Data were analyzed using ANOVA (95% confidence). Torsion tests showed a decrease in the instruments torsional resistance after clinical use, this decrease being statistically significant for the instruments S2, F1 and F2 of the LP group, and F1 and F2 of the NLP group. There was also a significant reduction in the fatigue resistance of all instruments after clinical use. The lateral pressure motion produced a tendency to decrease both the maximum torque and the NCF of S1 and S2 instruments, as well as to increase them in F1 and F2, although without a significant difference in these parameters. Qualitative analysis of the images obtained by scanning electron microscopy showed predominance of transverse cracks in the instruments submitted to lateral pressure motion and of longitudinal cracks in the instruments of the NLP group. Despite the reduction in torsional and fatigue resistance caused by the clinical use, ProTaper Universal instruments proved to be safe in cleaning and shaping 5 molars.