| Objective. The objective of this study was to quantify the properties of 11 commercially available nickel-titanium open-coil springs.;Methods. An Instron universal testing machine was used to measure the force generated when open-coil springs were compressed to one-half their original length and then unloaded. Eleven springs from 3 different manufacturers were tested at 5 testing sessions over a 12-week period.;Results. The average forces generated at the initial recording session for uniformly wound springs from GAC International and 3M Unitek(TM) were 19.3-42.7% and 9.7-38.8% below the manufacturers labeled force levels, respectively. GAC International 100g, 150g and 200g stop-wound coils demonstrated stepwise statistically and clinically significant force degradation over the 12-week period (p<0.0001). Uniformly wound coil, specifically GAC International, light (100g) coils generated the lowest load/deflection ratios (23.7 g/mm).;Conclusions. Uniformly wound coils may produce lower load/deflection ratios, and lower maximum forces, which are generally considered more acceptable for tooth movement. |
