ELECTROCHEMICAL STUDY OF INSULATING PROPERTIES OF DENTAL AMALGAM BONDING POLYMERS

The standard techniques used for amalgam restorations often result in a lack of adhesion to mineralized dental tissues. The bonding of amalg am with polymer has been suggested to improve its adaptation to dental tissues. Moreover the polymer involved in the bonding should inhibit the corrosion and the diffusion of metallic ions. The aim of this stud y was to evaluate in vitro the capacity of bonded amalgam to prevent i onic diffusion and migration. In this respect, an original method empl oying electrochemical techniques was used to determine the leakage cur rent of bonded amalgam restorations. The electrochemical behaviour of conventional and bonded amalgam restorations was compared using a pote ntiostat driven by a computerized system (Voltamaster, Radiometer Anal ytical) with software for specific applications such as chronoamperome try or cyclic voltammetry. Samples of recently extracted teeth of youn g patients were first examined, and then the results were checked by o ther experimental assays using protected and unprotected copper sticks . The measurements obtained with chronoamperometry (E = +300 mV/SCE) i n Ringer's solution at 37 degrees C showed that after polarization for 30 h the oxidation current decreased threefold for bonded samples (10 mu A cm(-2)) as compared with the unprotected samples (35 mu A cm(-2) )(.) These results, as well as those obtained with the copper wires, d emonstrated that even with two layers of adhesive the bonded joint is permeable to ions probably as a result of the hydrophylic properties o f HEMA, a component of the adhesive. However, using five layers of adh esive reduced the ionic current by a factor as large as 10(6).