CORROSION OF INTRAORAL MAGNETS IN THE PRESENCE AND ABSENCE OF BIOFILMS OF STREPTOCOCCUS-SANGUIS

Intra-oral magnets are used in dentistry for a variety of purposes, an d their susceptibility to corrosion is of great clinical importance. A lthough a number of in vitro models have been developed to study corro sion of intra-oral magnets, none have attempted to determine the possi ble contribution to corrosion made by oral bacteria, which are known t o form a biofilm on intra-oral appliances. We have exposed demagnetize d neodymium/iron/boron (Nd2Fe14B) magnets to an artificial saliva in t he presence and absence of a biofilm of Streptococcus sanguis, one of the predominant organisms in the oral cavity. Over a 21-d period, a 3. 2% decrease in the mass of the magnets was observed when S. sanguis wa s present, while in the absence of the organism the decrease in mass w as 1.4%. We also examined the ability of poly(para-xylylene), a common ly-used coating, to protect the magnets against corrosion. No decrease in the mass of magnets coated with poly(para-xylylene) was detected o ver a 21-d period in the presence of S. sanguis. This study has shown that biofilms of S. sanguis cause appreciable corrosion of Nd2Fe14B ma gnets which is greater than that occurring in the absence of the organ ism, and that a coating of poly(para-xylylene) provides protection aga inst such corrosion.