Corrosion of Dental Amalgam and its Component Phases

¹ Department of Materials Science, School of Engineering and Applied Science, University of Virginia, Charlottesville, Virginia

The effects of artificial saliva on the surfaces of the individual phases of dental amalgam have been observed by optical and electron microscopy and have been correlated with measured corrosion potentials and currents.

The ₂ phase (Sn₈Hg) had the most active potential and was observed to be the most severely attacked phase, the type of attack being general pitting.

The phase (Ag₃Sn) had an almost neutral potential and observations showed little attack or deposition, as there was only light etching.

The ₁ phase (Ag₂Hg₃) had a noble potential and was observed to develop a deposit, identified as AgCl, during anodic polarization.

Although some hindrance to dissolution was found as the potential was increased, no true passivity developed. It appeared, therefore, that little protection was offered by film formation in an oral environment.

The measured corrosion current of about 9µ amp./cm.² for dental amalgam in artificial saliva indicated a potentially rather drastic corrosion rate. Evidently, the high circuit resistance in a true oral environment is the factor that limits the amount of corrosion that actually occurs.