ABSTRACT
The aim of this study was to compare the characteristics of deflection load of three kinds of nickel titanium closed coil springs. This research was an experimental study. Research sample contains three kinds of NiTi closed coiled springs [heavy, medium, light] from GAC, 3M, and RMO factories. 10 springs with 9 mm length for each group [totally 90 springs] were subjected to tensile test. They were pulled to 12 mm extension by Dartec machine and then were released. Our variables were maximum force at 12 mm extension, force at the start of the plateau, deflection at the start of plateau, mean force of plateau, plateau slope, force at the end of plateau, deflection at the end of plateau. For tensile test, we used DARTEC universal machine. The data were analyzed by ANOVA and Duncan tests. In comparision among identical coils from different factories, the deflection at the end of plateau hadn't significant difference [P=0.107] but the other parameters had significant differences [P<0.001]. Among heavy coils, the maximum force of coil had statistically significant difference between 3M and GAC heavy coils. In medium coils, the maximum force of three kinds of springs had significant differences with each other [P<0.001]. In comparision among light springs, maximum force of coils had significant differences with each other. Mean force of plateau among the identical types of different manufacturer and among the different types of one factory had significant differences [P<0.001]. Only light type of RMO coil springs had a favorable force for tooth movements. In GAC and 3M springs, the medium type is recommended for canine retraction