CORROSION OF INTRAORAL MAGNETS BY MULTISPECIES BIOFILMS IN THE PRESENCE AND ABSENCE OF SUCROSE

The purpose of this study was to determine the corrosive effects of mu lti-species biofilms on intra-oral magnets in the presence and absence of sucrose. Using pooled human saliva as an inoculum, biofilms were g rown on the surfaces of 90 neodymium-iron-boron (Nd2Fe14B) magnets in a constant depth film fermenter under aerobic conditions at 37 degrees C. The fluid phase was a mucin-containing artificial saliva (delivere d at a rate of 0.72/litres day(-1)), and, after 15 days, 100 ml of 10% (w/v) sucrose was added (as three pulses of 33.3 ml) each day for a f urther 15 days. Six magnets with attached biofilms were removed period ically. On each sampling occasion the numbers of aerobes, anaerobes, s treptococci, veillonellae and actinomyces in each biofilm, the pH of t he fermenter effluent and the dry mass of the magnets were determined. Addition of sucrose to the fermenter resulted in a fall in pH (from a mean of 6.94 to a mean of 4.96), an increase in the proportion of str eptococci and a decrease in the proportion of veillonellae comprising the biofilms. The decrease in mass of the magnets was 28-fold greater in the presence of sucrose than in its absence. The results of this st udy have shown that the presence of sucrose affects the microbial comp osition of multi-species biofilms growing on Nd2Fe14B magnets and resu lts in a marked increase in corrosion of the magnets. (C) 1996 Elsevie r Science Limited