In vivo study on metal release from fixed orthodontic appliances and DNA damage in oral mucosa cells

Interest in the amount of metal ion intake from dental alloys has grown. Fixed orthodontic appliances usually include brackets, bands, and archwires made of stainless steel, nickel-titanium, or nickel-cobalt alloys, and these can release metal ions. The purpose of this study was to investigate the biocompatibility in vivo of fixed orthodontic appliances, evaluating the presence of metal ions in oral mucosa cells, their cytotoxicity, and their possible genotoxic effects. Mucosa samples were collected by gentle brushing of the internal part of the right and left cheeks of 55 orthodontic patients and 30 control subjects who were not receiving orthodontic treatment. The cells were immediately prepared for cell viability and the comet assay. Nickel and cobalt cellular content was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The results indicate that nickel and cobalt concentrations were 3.4-fold and 2.8-fold higher, respectively, in the patients than in the controls; cellular viability was significantly lower in the patients than in the controls, and there was a significant negative correlation with metal levels. The biologic effects, evaluated by alkaline comet assay, indicated that both metals induced DNA damage (more cells with comets and apoptotic cells). There were significant positive correlations between (1) cobalt levels and the number of comets and apoptotic cells, (2) nickel levels and number of comet cells, and (3) cobalt levels and comet tails. This study corroborates that nickel and cobalt released from fixed orthodontic appliances can induce DNA damage in oral mucosa cells.