Effects of recycling on the mechanical properties and the surface topography of nickel-titanium alloy wires.

The purpose of this study was to investigate the changes in mechanical properties, surface topography, and frictional forces of various nickel-titanium wires after recycling. Three types of nickel-titanium wires were separated into 3 groups: as-received condition (T0, control group), treated in artificial saliva for 4 weeks (T1), and treated in artificial saliva and autoclaved (T2). Strength changes were observed by tensile testing, and surface topography was assessed by scanning electron microscope and 3-D profilogram. Frictional coefficients were tested by friction test, and fatigue by bending fatigue test. Our findings showed that there were no statistically significant differences between the wires in maximum tensile strength, elongation rate, modulus of elasticity, and bending fatigue. Two wires demonstrated increased pitting and corrosion after recycling. The same 2 wires also demonstrated significantly greater surface roughness and maximum frictional coefficients compared with the control wires (P <.05), but the third wire showed no significant difference. However, surface roughness and frictional coefficient of the 2 wires after recycling were not greater than those of the third wire before treatment. Recycling increased the surface roughness and friction coefficients, but these seemed to have limited clinical significance.