Corrosion analysis of orthodontic brackets and arch wires – An in vitro study

Orthodontic plates are fixed onto the teeth in a dynamic environment in the oral cavity. The Orthodontic appliances, which includes both the brackets and the arch wires, are exposed to different pH fluctuations in the mouth. These appliances are manufactured using metal alloys that made out from nickel, iron, cadmium and titanium. These are commercially available in Sri Lanka and in the international market in different prices covering a large price range. Recent studies are investigating on the biocompatibility of these materials with the aim of determining the upper limit of the biological tolerance and to find methods to maintain ion release within acceptable limits. According to the previous studies there are evidences that the Ni and Cr ions release from Ni-Cr alloy in the presence of different acidity of artificial saliva. In this research in vitro corrosion process of selected orthodontic wires in artificial saliva solutions were evaluated with the aim of identifying a relationship between the quality and the price of selected orthodontic appliances available in Sri Lankan market. Eighteen specimens from different brands were selected and immersed in each of different types of artificial saliva at different pH, for different storage periods. All the sample tubes were incubated at 37°C. The release of metal ions from specimens with time were studied by conductivity, Atomic Absorption Spectroscopic (AAS) and mass loss measurements. According to the results, all specimens prepared using Ni -Ti wires release Ni²⁺ in the range between 9 ppm – 20 ppm during one year study period. Ni²⁺ concentration in all saliva solutions has increased with time and in specimens B, D, E, F the Ni²⁺ releasing rates were decreased with time. According to this study, all brands of brackets which were used in this study may lead to develop nickel hypersensitivity with time.