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Background: In the oral cavity, many bacteria can only survive by adhering to hard surfaces. The roughness and free energy of these surfaces play an important part in this process. Precision dental alloys may undergo corrosion, but findings show that this does not seem to cause problems of biocompatibility. The release of metallic ions into the oral cavity may both inhibit bacterial growth and influence bacterial adhesion. The object of the present study was to bring to light any possible correlation between corrosion and/or ionic release and bacterial adhesion with regard to 18 different types of dental alloy, both before and after polishing., Methods: Electrochemical analyses were carried out (cyclic potentiodynamic and potentiostatic polarisation tests). Corrodible elements were analysed through Atomic Absorption Spectroscopy of specimens of each alloy. The inhibition of bacterial adhesion and growth was determined using bacteria specific to the oral cavity., Results: All the alloys examined show a tendency towards spontaneous passivation with low values of anodic current. The evaluation of ionic release confirmed the biocompatibility of the tested materials and the solutions conditioned with the alloys did not inhibit bacterial growth. There was no significant bacterial adhesion after polishing. Bacteria adhere to unpolished alloys in a specific manner and are inhibited from doing so in the presence of alloys for gold-resin restorations containing silver and copper., Conclusions: When polished, all the alloys are resistant to in vitro electrochemical corrosion and bacterial adhesion. The possibility cannot be excluded that bacterial adhesion occurs after the materials have been in place in the oral cavity for some time. The alloys which were found to inhibit bacterial attack may be more suitable, while not representing a biological risk for the surrounding tissues.

A large number of methods are now available for the preclinical screening of implantable materials concerning their biocompatibility and their ability to stimulate tissue formation. In vitro techniques represent a very useful tool, since this way we can realistically simulate the biological events which occur in vivo at the bone-implant interface. In the present study scanning electron microscopy and light microscopy observations were performed in order to assess the effect of an hydroxyapatite granulate on cell behaviour and morphology. Uptake of proteins to hydroxyapatite surface has been also investigated by comparing the amounts adsorbed after incubation with bovine serum albumin and bovine pancreaticamilase. According to our preliminary observation cells do not show signs of toxicity or inhibition of cell growth even after 14 days of co-culture with hydroxyapatite. Granules were covered by an uninterrupted cell layer by day seven. Even after two days micrographs show cells anchored and spread over the surface of the underlying granules, with a flattened and stellate shape. Such a morphology indicates a very high cellular activity, suggesting that the interaction with hydroxyapatite seriously increased metabolism. Measurements of protein adsorption on the hydroxyapatite surface show that changes in the size of particles affect the binding of proteins, while, in the case of granular hydroxyapatite, despite changes in size of granules, variations of protein adsorption were not observed, neither in relation to their different isoelectric point. Our preliminary results represent a good example of the opportunities presented by an experimental in vitro model.