Release of metal ions from fixed orthodontic appliance An in vitro study in continuous flow system

Objective: To evaluate the release of metal ions from fixed orthodontic appliances. Materials and Methods: A new system for in vitro testing of dental materials was constructed and consisted of a thermostatic glass reactor that enabled immersion of the studied material. Experimental conditions reflected the human oral cavity, with a temperature of 37 degrees C and a saliva flow rate of 0.5 mL/min. The simulated fixed orthodontic appliance made of stainless steel was evaluated. Sampling was performed at several time points during the 28-day study, and the metal ion concentration was determined by inductively coupled plasma optical emission spectrometry. Results: The total mass of released metal ions from the appliance during 4 weeks of the experiment was as follows: nickel 18.7 mu g, chromium 5.47 mu g, copper 31.3 mu g. Conclusions: The estimated doses of nickel, chromium, and copper (determined by extrapolation of experimental data) released during the treatment period were far below the toxic dose to humans. This shows that orthodontic treatment might not be a significant source of exposure to these metal ions.