Guthrow, C. E., Johnson, L. B. and Lawless, K. R.,  “Corrosion of Dental Amalgam and its Component Phases”, J. Dent. Res. 46(6): 1372-1381, 1967

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./cm² 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.

Von Fraunhofer, J. A. and Staheli, P. J., “Corrosion of Dental Amalgam”, Nature 240, 304 - 306 (01 December 1972)

DENTAL amalgam is incorporated into about 80% of all dental restorations. It is prepared by grinding or triturating a silver−tin alloy (Ag3Sn, the  phase) with mercury in the proportions 1 : 1 or 5 : 6 of alloy to mercury. The setting reaction of dental amalgam has been studied by many workers1−4 and is now accepted to be  Excess mercury is removed from the amalgam both before and during insertion into the cavity. There is, however, some controversy over whether the 2 phase is continuous throughout the matrix5 or whether it is present in discrete clumps or clusters (G. Wing, personal communication).

 References

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12. Guthrow, C. E. , Johnson, L. B. , and Lawless, K. R. , J. Dent. Res., 46, 1372 (1967).

13. Carter, D. , Ross, T. , and Smith, D. , Br. Corros. J., 2, 199 (1967).

14. von Fraunhofer, J. A. , and Staheli, P. J. , Br. Dent. J., 130, 522 (1971).

15. von Fraunhofer, J. A. , and Staheli, P. J. , Br. Dent. J., 132, 357 (1972).

16. Jenkins, G. N. , The Physiology of the Mouth, third edition, 317 (Oxford, Blackwell, 1967).