Effect of Recycling and Autoclave Sterilization on the Unloading Forces of NiTi Closed-Coil Springs: An In Vitro Study.
BACKGROUND
Clinicians use the NiTi coil springs frequently for its appropriate mechanical properties.


OBJECTIVE
The aim of this study was to determine the effect of recycling and autoclave sterilization on the unloading forces of NiTi closed coil springs.


METHODS
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.


CONCLUSIONS
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.
Dept. of Orthodontics, Member of Orthodontic Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
Sh
Sh
Momeni Danaei
Dept. of Orthodontics, Member of Orthodontic Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
M
M
Oshagh
Orthodontist, Dept. of Orthodontics, International Branch, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
A
A
Khozaei
Closed-coil Springs; NiTi; Recycling