Decalcification is a commonly recognized complication of orthodontic treatment with fixed appliances. A technology, based on a parallel plate flow chamber, was developed to investigate early biofilm formation of a strain of Streptococcus sanguis on the surface of four orthodontic bonding materials: glass ionomer cement (Ketac Cem), resin-modified glass ionomer cement (Fuji Ortho LC), chemically-cured composite resin (Concise) and light-cured composite resin (Transbond XT). S. sanguis was used as it is one of the primary colonizers of dental hard surfaces. Artificial saliva was supplied as a source of nutrients for the biofilms. The effects of two commercially available mouthrinses (i.e. a fluoride containing rinse and chlorhexidine) were evaluated. Initial colonization of the bacterium was assessed after 6 hours of growth by the percentage surface coverage (PSC) of the biofilm on the disc surfaces.There were statistically significant differences in bacterial accumulation between different bonding materials (P < 0.05), Concise being the least colonized and Transbond XT being the most colonized by S. sanguis biofilms. All materials pre-treated with 0.05 per cent sodium fluoride mouthrinse showed more than 50 per cent reduction in biofilm formation. The 0.2 per cent chlorhexidine gluconate mouthrinse caused significant reduction of biofilm formation on all materials except Ketac Cem.This in vitro study showed that the use of a chemically-cured composite resin (Concise) reduced early S. sanguis biofilm formation. Also, fluoride had a greater effect in reducing the PSC by S. sanguis biofilms than chlorhexidine. Rinsing with 0.05 per cent sodium fluoride prior to placement of orthodontic appliances is effective in reducing early biofilm formation.

The aim of this study was to investigate the accumulation and composition of microcosm dental plaque on different orthodontic bonding materials using an in vitro model. Microcosm plaques were grown on discs of a range of bonding materials in a constant depth film fermentor. The biofilms were derived from human saliva and supplied with artificial saliva as a source of nutrients. The number of viable bacteria in the biofilms was determined and the streptococci present were identified to species level. The results showed that there was no significant difference in bacterial accumulation between different bonding materials, however, biofilms grown on materials which were fluoride releasing, did not contain Streptococcus mutans. This in vitro study has shown that the use of fluoride-releasing bonding materials may support the growth of supragingival plaque, which does not contain S. mutans.

The aim of this investigation was to study the corrosion behaviour and products of uncoated neodymium-iron-boron magnets in the presence of dental amalgam. Microcosm plaques were grown on discs of neodymium-iron-boron magnets or amalgam in a constant depth film fermentor. The biofilms were supplied with artificial saliva and growth was determined by viable counting. The results showed that the neodymium-iron-boron magnets corroded with an average daily weight loss of 0.115 +/- 0.032 per cent. However, when the magnets were in close proximity to the amalgam the amount of corrosion was reduced to a daily loss of 0.066 +/- 0.023 per cent. The highest loss of constituent elements from the corrosion products of the magnets was observed for iron. The composition of the microcosm plaques altered markedly between the two materials with less streptococci and more Veillonella spp. present in the biofilms grown on magnets in the presence of amalgam. The corrosion of neodymium-iron-boron magnets is limited and in the presence of amalgam is reduced further. This suggests that amalgam present in the mouth will not cause an increased clinical risk in terms of biocompatibility with neodymium-iron-boron magnets.