In vivo galvanic currents of intermittently contacting dental amalgam and other metallic restorations

It was the objective of this study to determine the magnitude of in vivo galvanic currents produced by simulating electrical contact between occluding metallic restorations, and to examine the influence of restoration age, difference in pre-contact corrosion potentials, and surface area.

A convenience sample of 106 human subjects was studied. A Ag/AgCl micro-reference electrode and a high impedance voltmeter were used to measure the pre-contact corrosion potentials. Galvanic couples (n = 194) were next formed by simultaneously contacting occluding restorations with gold-plated probe tips for 15 s. The resulting current-time transients were measured with a zero-resistance ammeter and recorded with an electronic data acquisition program. The vast majority of couples measured contained at least one dental amalgam restoration.

Galvanic current-time transients were typically characterized by an immediate and rapid rise to a peak current, followed by an exponential decay to a much lower value at 15 s. For couples with a restoration < or = 12 mo old, median peak current and median current at 15 s were 2.26 microA (range 0.24-13.06 microA) and 0.57 microA (range 0.03-6.47 microA), respectively. For couples with a restoration >12 mo old, median peak current and median current at 15 s were 1.40 microA (range 0.24-12.09 microA) and 0.37 microA (range 0.00-3.05 microA), respectively. Couples with fresh amalgams (< or = 6 mo) generally had elevated currents (range 2.56-102.54 microA).

A wide range of galvanic currents resulted from electrical contact of restorations in vivo. These currents were influenced by restoration age and total surface area of the galvanic couple. For amalgam-amalgam couples, the difference in the pre-contact corrosion potentials may be useful in predicting galvanic currents, when the difference is at least 24 mV.