Ion release from orthodontic appliances

Objective: The microbiological and enzymatic characteristics of the oral ca vity would seem to provide a suitable environment for the corrosion of meta ls. We assayed the release of metal ions from one orthodontic appliance whi ch included two 304 and 316 steel molar bands, ten 316 steel brackets, one nickel-titanium archwire and a brazing alloy to connect the elements of mol ar bands and brackets. Methods: The orthodontic appliance was dipped in both inorganic (pH 3.5-6.5 ) and organic acid solutions (w/v 1% each of tartaric, citric and ascorbic acid at pH 2.2 or 1.5% each of lactic and acetic acid at pH 2.5). The relea se of nickel (Ni), chromium (Cr), copper (Cu), silver (AE) and palladium (P d) was determined using an atomic absorption spectrophotometer Varian AA 10 . Results: The release of Ni, Cr and Cu was markedly less at pH 6.5 than at p H 3.5 at all time points in acid solution. Daily release/single appliance a fter the first day decreased. Contrary to expectations, appliances immersed in organic acid solutions at pH 2.2 or 2.5 after 28 days generally release d an amount of ions similar to that observed in inorganic acid solution at pH 3.5, with the exception of Cu. Release of silver and palladium, two meta ls present in the brazing alloy, proved to be very low (approximately 0.2 m u g after 28 days). Conclusions: The daily release of Ni, Cu and Cr by an orthodontic appliance in acid pH, particularly favourable to corrosion, was well below that inge sted with a normal daily diet. It is therefore concluded that the quantitie s of metal ions released in our experimental conditions should not be cause for concern in utilising the appliance. (C) 1999 Elsevier Science Ltd. All rights reserved.