Existence of an electrically insulating layer in amalgam-containing galvanic couples

Sutow, Elliott J.; Taylor, James C.; Maillet, Wayne A.; Hall, Gordon C.; Millar, Michele

doi:10.1016/j.dental.2007.11.002

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Volume 24, Issue 7 , Pages 874-879, July 2008

Existence of an electrically insulating layer in amalgam-containing galvanic couples

Elliott J. Sutow
- Department of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, Canada B3H 3J5
- Corresponding author. Tel.: +1 902 494 8813; fax: +1 902 494 6621.
James C. Taylor
- Department of Dental Clinical Sciences, Faculty of Dentistry, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, Canada B3H 3J5
Wayne A. Maillet
- Department of Dental Clinical Sciences, Faculty of Dentistry, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, Canada B3H 3J5
Gordon C. Hall
- Department of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia, Canada B3H 3J5
Michele Millar
- Department of Mathematics, Mount Saint Vincent University, Halifax, Nova Scotia, Canada B3M 2J6

Received 29 June 2007; received in revised form 5 October 2007; accepted 4 November 2007.

Abstract

Objective

Avoiding the placement of amalgam and noble metal restorations in interproximal contact is recommended due to anticipated galvanic corrosion of the amalgam. There is a similar concern for amalgam/amalgam galvanic couples. It was the objective of this study to determine if an electrically insulating layer forms in the contact area of these galvanic couples. The existence of an electrically insulating layer, which could reduce the galvanic corrosion rate, would be indicated by different corrosion potentials for the two restorations of the couple.

Methods

Using a convenience sample of 158 human subjects, corrosion potentials were measured on each restoration of three types of galvanic couples: amalgam/noble metal (n=8), amalgam/amalgam (n=93) and noble metal/noble metal (n=7). Measurements were made with a Ag/AgCl micro-reference electrode and a high impedance voltmeter. All restorations were at least 6 months old.

Results

Statistical analysis showed that the mean absolute corrosion potential differences and the simultaneous confidence intervals of the couples were, respectively, amalgam/noble metal: 62 (31)mV and (27, 99)mV, amalgam/amalgam: 11 (14)mV and (7, 15)mV and noble metal/noble metal: 7 (10)mV and (0, 19)mV.

Significance

The amalgam/noble metal couples had consistent and mostly large corrosion potential differences between their restorations, which indicated the presence of an electrically insulating layer. An electrically insulating layer was also indicated for the amalgam/amalgam and noble metal/noble metal couples. The layer is probably composed of non-metallic corrosion products, biofilms, and possibly, dental calculus, which could reduce galvanic corrosion rates to small or negligible values.

Keywords: Galvanic corrosion, Electrically insulating layer, In vivo, Amalgam, Noble metal