FORCE GENERATION BY ORTHODONTIC COIL SPRINGS

Nickel titanium (NiTi) coil springs are a new development in orthodont ics, designed to produce light continuous forces. This study compares the force delivery by NiTi open and closed coil springs during unloadi ng (de-activation) to that provided by comparable stainless steel (SS) springs. Open-coil springs (0.010x0.035 inch) were compressed from th eir initial length of 15 mm to 6 mm and the forces generated with spri ng recovery recorded. Closed-coil springs (0.009x0.035 inch) were dist racted from their initial length of 3 mm to 9 mm and the force recorde d as the spring recovered. The closed-coil NiTi springs produced light continuous forces of 75-90 g over the distraction range of 6 mm while the open-coil springs produced forces of 55-70 g within the 9 mm comp ression range. SS springs produced heavier forces, ca. 200 g, for an a ctivation of 1 mm and the generated force increased rapidly as the act ivation was increased. The findings indicate that NiTi coil springs de liver optimal forces for orthodontic tooth movement over a longer acti vation range than comparable SS springs.