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The effect of different sodium chloride concentrations on the integrated currents (charge transfers) between dental amalgams and a gold alloy was studied in a bimetallic cell containing saliva or saline solutions. The integrated currents were only to a minor degree affected by increasing chloride concentrations for the high copper amalgams both in saliva and saline solutions. The integrated currents in the experiments involving conventional amalgam were several times higher than those for high copper amalgams. In saline solutions a charge transfer maximum was found at 0.2 M chloride. In saliva an increase of the charge transfer was found with increasing chloride content.

The galvanic currents between amalgam and gold alloy electrodes were higher in saline solutions than in saliva. Conventional amalgam supported higher currents than high copper amalgams when short-circuited with a gold alloy. The galvanic currents were not affected or affected only to a very small degree when whole saliva from different persons were compared. Higher currents were recorded when short-circuiting conventional amalgam and gold alloy electrodes using parotid saliva than when using whole saliva collected from one person. However, removing molecules with a molecular weight higher than 10(4) from whole and parotid saliva did not seem to affect the galvanic currents.

Short-circuited electrodes of dental amalgams and a gold alloy were used in an attempt to study a possible relationship between the quantity of copper and tin ions released into an electrolyte and the charge transferred between the electrodes. It was found that under the experimental conditions used the quantity of tin ions released was related to the charge transferred between the conventional amalgam and the gold alloy. The same tendency was found using a saliva sample which confined and collected the released tin ions into a small volume when the conventional amalgam specimen was short-circuited to the gold alloy specimen in vivo.

Thirty referred patients and 15 control subjects were investigated with reference to the occurrence of bimetallic corrosion in the oral cavity. No differences between patients and controls could be found regarding the registered charge transfer between dissimilar short-circuited dental metallic restorations and/or appliances. However, a relatively large number of periodontal and mucous membrane affections, carious lesions and stomatognathic and/or temporomandibular joint disturbances were found within the patient group.

The marginal degradation and corrosion of restorations made of a high copper dispersed amalgam were studied as a function of time for up to 5-yr observation periods. The effect of minor defects present after finishing the restorations was included in the assessment of the initial marginal degradation. A slow progressive marginal degradation was noted and it was enhanced by initial defects. Subsurface corrosion including attacks of the phase and grain boundaries, corrosion within the bulk, and layers of corrosion products along the tooth/restoration interfaces were observed in restorations after some years in clinical service. The subsurface corrosion is considered to weaken the amalgam and it might enhance the marginal degradation, i.e. a stress corrosion type of degradation.