Journal of Dental Research, Vol 67, 1275-1277, Copyright © 1988 by International & American Associations for Dental Research Online Journals
Sn in the Ag-Hg phase of dental amalgam
D. B. Mahler and J. D. Adey
Oregon Health Sciences University, School of Dentistry, Portland 97201.
In a recent study, Sarkar and Eyer (1986) studied an amalgam which was
formed using a unique procedure. Based on their results, they concluded
that the solubility of Sn in the Ag-Hg (gamma 1) phase of dental amalgam
was virtually nil (less than 0.25 wt%). This finding is contrary to the
published results of other investigations. The purpose of the present study
was to clarify these disparate findings. A low-copper dental amalgam was
examined by electron probe microanalysis. This amalgam was selected because
it exhibits unusually large gamma 1 grains (10 microns). Because the
influence of the electron-analyzing beam can be completely contained within
these large grains, grain boundaries or peripheral phases would not be
excited, and a valid analysis of the gamma 1 grains themselves could be
made. The analyses showed significant Sn contents of 2.0-3.0 wt%. Analyses
of areas which contained grain boundaries showed slight or no differences
in Sn content compared with that for the grains alone. Furthermore,
secondary electron scans of this dental amalgam failed to reveal the
intergranular precipitates of Sn-Hg observed by Sarkar and Eyer (1986) in
their amalgam. These different results can be explained by the fact that
the unique amalgam investigated by Sarkar and Eyer does not exhibit the
same diffusional patterns as does dental amalgam, and that the composition
of the gamma 1 in the two amalgams is not the same. The final conclusion is
that the Ag-Hg (gamma 1) phase in dental amalgam does indeed contain a
significant amount of Sn.
