Berit I. Johansson

Corrosion of titanium and amalgam couples: Effect of fluoride, area size, surface preparation and fabrication procedures

OBJECTIVES The aim of this investigation was to study the effect of surface treatments and electrode area size on the corrosion of cast and machined titanium in contact with conventional and high-copper amalgams in saline solutions with and without added fluoride ions. METHODS The potentials and the charges transferred between amalgam and titanium couples were registered using standard electrochemical methods. RESULTS Conventional amalgam corroded more than high-copper amalgams in contact with titanium in saline solutions. Adding fluoride to the solution made the titanium potential more active and enhanced the corrosion of titanium in combination with high-copper amalgams. The amalgam corrosion increased with a five-fold enlargement of the titanium area. The increase was significant for one titanium-amalgam combination. Surface preparations affected the electrochemical behavior, and surface alterations were occasionally observed on wet-ground titanium specimens. No significant differences were found in comparisons of cast and lathe-cut titanium. SIGNIFICANCE Surface preparations and fluoride affect the electrochemical activity of titanium.

Effects of titanium-dental restorative alloy galvanic couples on cultured cells.

The potential exists for titanium and amalgams to become galvanically coupled in the oral cavity. While low galvanic corrosion rates have been measured in vivo for titanium-amalgam or mercury-free alloy couples, concerns exist over released corrosion products and adverse tissue responses. It was hypothesized in this study that coupling titanium to amalgams or gallium alloys increased the release of metallic corrosion products and decreased cellular activity and function. The effects of titanium coupled and uncoupled to a conventional amalgam, palladium-enriched spherical high copper amalgam, a dispersed type high copper amalgam, and a mercury-free gallium alloy were evaluated in 24-h cell culture tests. Viability, proliferation, and collagen synthesis were evaluated by the uptake of neutral red, 3H-thymidine, and immunoassay of procollagen, respectively, and compared to cells not exposed to any test material. The gallium alloy-titanium couple resulted in significant decreases in cellular viability, proliferation, and collagen synthesis as compared to the other coupled and uncoupled samples. Few differences in the cellular responses of the other coupled and uncoupled samples were observed. Atomic absorption analyses indicated increased release of metal ions from the amalgam and gallium alloy samples coupled to titanium as compared to their uncoupled condition, although the differences were not always significant. Galvanic corrosion of amalgam-titanium couples in the long term may become significant, and further research is needed. Coupling the gallium alloy to titanium may result in increased galvanic corrosion and cytotoxic responses.