Influência dos processos de esterilização nas propriedades mecânicas de instrumentos endodônticos de NiTi

Abstract

Thermo-mechanical treatments applied industrially can improve the properties of NiTi alloy used in the manufacture of rotary endodontic instruments. However, the effect of sterilization on the mechanical properties of these instruments is not yet fully established. The present study evaluates the effect of five consecutive sterilization cycles, in dry heat oven or steam autoclave, on the mechanical properties of NiTi instruments, which were tested to failure in torsion and in flexural fatigue. Vickers Microhardness measurements were carried out on the instruments shaft before and after sterilization. NiTi wires employed in the manufacture of the instruments were sterilized in a similar way and then tensile tested until rupture. The influence of sterilization on instruments fatigue tested until one half of their fatigue life was also evaluated. The Students t test at 95% confidence level was used for statistical analysis of the results obtained. The sterilization procedures did not cause a significantly change in the hardness of the analysed instruments. Similarly, their torsional behaviour and the mechanical properties of the tensile-tested wires were only slightly influenced by sterilization. However, there was a significant increase in the fatigue resistance of all sterilized instruments, especially in those submitted to cyclic deformation previously to sterilization. From the clinical point of view, the results obtained indicate that the sterilization procedures enable safe reutilization of the NiTi instruments, by increasing their fatigue strength.