Silver-tin alloys and amalgams: electrochemical considerations

Area of Science:

• Materials Science
• Electrochemistry
• Biomaterials Science

Background:

• Dental amalgams, primarily silver-tin alloys, are widely used restorative materials.
• Understanding their corrosion behavior in physiological environments is crucial for longevity and biocompatibility.

Purpose of the Study:

• To determine the corrosion potential and anodic polarization profiles of silver-tin alloys and amalgams.
• To correlate corrosion behavior with alloy microstructure and tin content.
• To elucidate the electrochemical mechanisms underlying amalgam corrosion.

Main Methods:

• Electrochemical measurements including corrosion potential and anodic polarization.
• Microstructural analysis of silver-tin alloys and amalgams.
• Corrosion testing in a physiological solution.

Main Results:

• Corrosion in high-tin alloys (>27% wt) and amalgams is linked to free tin and gamma-2 tin phases, respectively.
• Gamma-2 tin concentration increases with tin content in amalgams.
• Low-tin alloys (<27% wt) exhibit restricted corrosion, even less than pure silver.
• A theory links O2 reduction on SnO films to H2O2, controlling overvoltage.
• Increased silver content in amalgams, especially 8-12% tin, reduces O2 reduction overvoltage.
• Polarization-induced corrosion creates a silver-mercury-rich phase on unreacted particles.

Conclusions:

• Corrosion resistance of silver-tin alloys and amalgams is significantly influenced by tin and silver content.
• The electrochemical mechanism involves tin oxidation and oxygen reduction on a tin oxide film.
• Optimizing alloy composition, particularly increasing silver content, can enhance amalgam durability in oral environments.