Force-distance relation and properties of repelling Sm-Co5 magnets in orthodontic clinical use: an experimental model.

In recent years, magnets and magnetic forces have been suggested as an alternative to traditional orthodontic devices such as elastics, springs and wires. The purpose of this study was to analyze the reliability and the output of forces for prefabricated orthodontic repelling Sm-Co5 magnets and the force conditions for the magnets after 5 months of maximal loading. The test-machine consisted of a jig where the tested pair of repelling magnets was mounted close to the clinical situation. With a cylindrical strain gauge transducer, a micrometer screw, a bridge-amplifier, and a Mingograph jet recorder, force-distance diagrams were constructed. The force-distance diagrams showed that the force-distance curve was hyperbolic and that the mean force when the magnetic pole faces were almost in contact with each other was 214.9 g, SD 13.42 g. The variation of magnetic force between different Sm-Co5 magnets was 6-9%. The difference in force before and after 5 months of maximal loading of the magnets was not significant. The test results indicate that with proper handling of the forces according to the new force diagrams, the system is reliable for orthodontic use.