Corrosion of intra-oral magnets in the presence and absence of biofilms of Streptococcus sanguis

Intra-oral magnets are used in dentistry for a variety of purposes, and their susceptibility to corrosion is of great clinical importance. Although a number of in vitro models have been developed to study corrosion of intra-oral magnets, none have attempted to determine the possible contribution to corrosion made by oral bacteria, which are known to form a biofilm on intra-oral appliances. We have exposed demagnetized neodymium/iron/boron (Nd2Fe14B) magnets to an artificial saliva in the 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 was present, while in the absence of the organism the decrease in mass was 1.4%. We also examined the ability of poly(para-xylylene), a commonly-used coating, to protect the magnets against corrosion. No decrease in the mass of magnets coated with poly(para-xylylene) was detected over a 21-d period in the presence of S. sanguis. This study has shown that biofilms of S. sanguis cause appreciable corrosion of Nd2Fe14B magnets which is greater than that occurring in the absence of the organism, and that a coating of poly(para-xylylene) provides protection against such corrosion.