DNA damage kinetics (micronucleus and comet assay) in buccal mucosa cells of subjects after metal fixed appliances

Orthodontic appliances are usually made of stainless steel, which contains metals (nickel, chromium, etc.) that have been associated with DNA damage. Therefore, data on the biocompatibility of alloys have created growing interest. The aim of this study was to determine the genetic toxicity associated with the kinetics of metal release from fixed orthodontic appliances in mucosa cells. Mucosa samples were collected, by brushing of internal cheeks of 25 patients, before (T0) and after 7 (T7), 15 (T15), 30 (T30), 60 (T60) and 90 (T90) days of orthodontic treatment. The cells were isolated for nickel (Ni), chromium (Cr) and titanium (Ti) content by inductively coupled plasma mass spectrometry (ICP-MS), glutathione (GSH) levels and the genotoxicity were evaluated by micronucleus (MN) and comet (CA) assay. The results indicate that after the placement of the orthodontic appliances there is a significant increase in Ni and Cr cellular concentration (p < 0.05 and p < 0.001, respectively), but not for Ti. DNA damage, as assessed by CA, is significantly high already at T15 (p < 0.001) in reference to T0. Conversely, there is a significant increase in MN frequency 30 days after the beginning of the orthodontic treatment (p < 0.001). These results show that CA detects DNA damages induced very early after exposure to genotoxic agents, while MN reveals after 30 days structural damages (chromosome breakage or spindle dysfunction), that occur in the dividing basal layer. CA and MN are significantly correlated each other, with day-exposure and with cellular Cr