Corrosion of orthodontic bracket bases.

Attention has recently been focused on the development of black and green stains in association with directly bonded stainless steel brackets. Twelve clinical cases of staining were studied in this investigation. After intraoral photography of the stains, the brackets were removed for examination with the scanning electron microscope. Multiple voids were observed at the resin-bracket interface, especially at the periphery. Considerable deterioration of the alloy base and mesh structure was observed in the void areas. Preliminary analysis of the stains showed that chromium compounds were present. The findings suggested that the presence of voids, together with poor oral hygiene, led to crevice corrosion of the Type 304 stainless steel and formation of colored corrosion products which can result in enamel stains. The use of stainless steels of improved corrosion resistance is recommended to overcome this problem.