Biocompatibility of new, clinically used, and recycled orthodontic samarium-cobalt magnets

The aim of this study was to compare the cytotoxic effect of new, clinically used, and recycled samarium-cobalt magnets (SmCO5). Cytotoxicity was assessed by two in vitro methods, the millipore filter method and an extraction method. In the filter method, the test material and the target cells are separated by a thin, permeable membrane. The test assesses the cytotoxicity of both water soluble and nonwater soluble components of the test material. The extraction test, which has a higher sensitivity, assesses the cytotoxicity of water soluble components only. According to the filter method, one magnet (new) showed a mild cytotoxic effect; all other tested magnets showed no cytotoxicity. Judged by the extraction test, new as well as clinically used magnets demonstrated a weak cytotoxic effect, suggesting the presence of a small amount of leachable cytotoxic components. The level of exerted cytotoxicity of such components was significantly lower for clinically used than for new magnets. When recycled magnets were tested, the cytotoxicity had significantly decreased, (p < 0.001), and the cytotoxicity could be considered negligible. The results thus revealed that SmCO5 magnets can be recycled with maintained good biocompatibility. Because a small amount of water soluble cytotoxic agents seem to leach out from new partially stainless steel-coated samarium-cobalt magnets, it is recommended that they be stored in water for 24 hours before clinical use, thereby conceivably decreasing the oral exposure of water soluble cytotoxic agents.