Bacterial adhesion to dental alloys. The role of the surface and composition

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.

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.

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.

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.