Journal of Dental Research, Vol 77, 1999-2004, Copyright © 1998 by International & American Associations for Dental Research Online Journals
Surface chemistry of a high-copper dental amalgam
A. J. McDermott, S. Kothari, R. D. Short, R. van Noort and M. R. Alexander
Laboratory for Surface & Interface Analysis, Department of Engineering Materials, Sheffield, United Kingdom.
In amalgam, mercury is intended to take the form of stable intermetallic
compounds. Any mercury leakage must therefore come from free mercury not
involved in such compounds. Thus, a knowledge of the exact surface
chemistry of dental amalgam is necessary if this phenomenon is to be
understood. From XPS and EDS analyses, a model of the surface chemistry of
amalgam is proposed which fully characterizes all the phases that are
present. The data show the surface to have a composition different from
that of the bulk, being comprised of a hydrocarbon deposit and adsorbed
water covering the intermetallic phase gamma2 (Sn(6-8)Hg), tin (iv) oxide,
and mercury in a free state. After amalgamation, the amount of mercury at
the surface decreases with time and eventually attains a constant
concentration, where it is all involved in the gamma2 phase, leaving no
free mercury. A model is proposed for the surface of amalgam and the
changes in this model with time.
