Accelerated corrosion analysis of dental amalgams

The corrosion of powdered conventional and high Cu dental amalgam was studied in vitro under fixed conditions (100% oxygen, pH 4, and constant weak mechanical action). Results were retrieved from X-ray diffraction of samples of amalgam and solid corrosion products formed, in combination with recording of the HCl consumed to maintain the fixed pH. In the conventional amalgam no corrosion of gamma 1 occurred until all gamma 2 had corroded, whereas in the high Cu amalgam corrosion of gamma 1 occurred from the beginning, concurrent with corrosion of epsilon and eta'. Corrosion products found were AgCl, Hg2Cl2, CuCl2 X 3Cu(OH)2, and SnO2. The results may be interpreted as follows: in the conventional amalgam the matrix phase gamma 1 is anodically protected against corrosion as long as any gamma 2 remains; in the high Cu amalgam the least noble phases epsilon and eta' do not protect gamma 1 in a similar way.