Corrosion of Dental Amalgam in Culture Media

Corrosion of dental amalgam may be greatly accelerated by the dental plaque which produces localized anodic area on the amalgam surface (VON FRAUNHOFER and STAHELI, Brit Dent J 130:522, 1971). Conversely, dental amalgam affects the dental plaque formation processes as suggested by the influence of dental amalgam on the in vitro growth of Streptococcus mutans (NUNEZ ET AL., J Dent Res 55:257, 893, 1001, 1976). Presented are results of a preliminary study on the relationships of dental plaque and restorative materials. Of particular interest were the corrosion products of dental amalgam beneath the dental plaque which can be detected by means of linear potential sweep method (NoMOTO, KOBAYASHI and ONOSE, J Dent Res, in press). The set polished dental amalgam electrodes (electrode area 0.126 cm2) prepared from the conventional type amalgam* were suspended in 16 X 120 mm test tubes containing 10 ml volume of Trypticaset salts broth (GIBBONS and FITZGERALD, J Bacteriol 98:341, 1969) supplemented with 5% sucrose (MGCABE, KEYES and HOWELL, Arch Oral Biol 12: 1653, 1967), which was inoculated with 0.1 ml of a 24-hour culture of Str'eptococcus mutans IB (uninoculated media served as control). Test tubes then were incubated anaerobically (95% nitrogen5% CO2) at 37 C; electrodes were transferred into freshly inoculated new media daily for 3 consecutive days. After removal from the medium under study, the electrode was transferred into the 0.86% NaCl aqueous solution. After 10 minutes equilibration in the solution, the electrode was cathodically polarized and then the direction of polarization was reversed with the sweep rate of 200 mv/sec. Typical polarization curves are illustrated in the figure. The electrode incubated in the inoculated medium showed reduction peak at 0.8v(SCE). This peak was not influenced by the immersion time in 0.86% NaCl aqueous solution, the removal of the streptococcal deposit formed on the electrode surface or wiping the