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.

 Source: Journal of Dentistry Shiraz University of Medical Sciences

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