Effect of Recycling and Autoclave Sterilization on the Unloading Forces of NiTiClosed-Coil Springs: An in Vitro Study

Statement of problem: clinicians use the niti coil springs frequently for its appropriate mechanical properties. purpose: the aim of this study was to determine the effect of recycling and autoclave sterilization on the unloading forces of niti closed coil springs. materials and method: fourteen niti closed coil spring with the length of 9mm were selected. each coil was stretched to a peak extension of 12 mm. a universal testing machine was used to acquire load/deflection curve of the coil springs at 25±2°c. the influence of thermocycling (1000 cycles,5-55°c), autoclaving (134°c, 32psi, 3min) and mechanical strain (9mm extension) which simulated the oral condition, were considered. data were statistically analyzed by adopting repeated measures manova paired t-test. results: autoclaving in the 1, 4, 6 steps increased the force levels of coil springs about 2- 5gf (p< 0.01). thermocycling reduced their force levels about 4-6gf. prolonged strain at 3, 5 steps decreased the magnitude of forces levels about 3-4gf. conclusion: concerning all the limitations; according to the results of this study; it is possible to recycle ni-ti closed-coil springs without significant reduction in their force levels.