[Evaluating the integrated force induced by high quality magnet and elastics in orthodontic fixed appliance].

Purpose: To investigate the stability and effective working distance of integrated forces induced by high quality magnet and elastics in orthodontic fixed appliance.

Methods: N48 NdFeB magnets resembling brackets in size and volume were combined with 1/8, 3/16, 1/4, and 3/8 inch orthodontic elastics respectively to induce integrated forces that had super-long working distance. Magnetic, elastic, and integrated forces were tested by universal material test system and curves of the forces were draw. The characteristics of integrated forces, complementary effects of magnetic and elastic forces, and the proportion between elastic and magnetic forces in integrated forces at different extension distances were analyzed. Unpaired t test was used to analyze the differences between integrated and elastic forces.

Results: With the increase of the extension distance, the magnitude of the magnetic forces decreased significantly and the elastic forces increased in a liner manner, while the integrated forces were stable and changed mildly. Four kinds of integrated forces achieved 86 g, 138 g, 163 g, and 192 g stable forces within super-long distance respectively. Magnetic forces accounted for 34.94%-93.98% of the integrated force at 3 mm distance, 12.60%-37.89% at 6 mm distance, and only 2.69%-5.98% at 12 mm distance. The differences between four integrated forces and elastic forces at 3 mm (P<0.01), 6 mm (P<0.01), and 9 mm distance (P<0.05) were significant.

Conclusion: Integrated forces composed of magnetic and elastic forces were a new ideal stable orthodontic force with super-long working distance.