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CHAPTER XX. a

]\rA\lPULAT10X OF COHESIVE GOLD IN THE MAKING OF
A FILLING.

Physical Properties. The physical properties most desired in n
.tilling are fonnd in cohesive gold to a greater degree than in any
other filling material, which places it at the head of the list as a
means of restoring lost contour and preventing recurrence of de-
cay. It is not affected by the fluids of the mouth; it may be very
perfectly adapted to the walls of the cavity; the shrinkage and ex-
pansion range in varying temperature is very slight; the cavity
can be filled immediately upon freshly cut surfaces before they
have been contaminated, an advantage over the fused inlay; and
when sufficiently condensed it possesses a greater specific gravity,
hence density, than a fused inlay of pure gold. Hammered gold
will flow under sufficient stress and always in proportion to the
load, when it ceases to flow, unless the load is increased—
marked distinction between it and amalgam. This quality of gold
makes it possible to build a filling which will at once sustain the
force of mastication provided it has received sufficient aggregate
Aveight during the process of introduction. This physical prop-
erty of gold is also of service in that it does not farther compress
when firmly wedged between the Avails of living dentine which are
elastic and retain a certain amount of residual elasticity Avhich
permanently grasps the unyielding gold. The expansion and con-
traction of gold under the varying oral temperatures is fully com-
pensated for by this residual elasticity of the dentine so that the
closely adapted cohesive gold filling is at all times in perfect
adaptation.
The Objectionable Qualities of Gold. Gold is a good conductor
of thermal changes, hence endangers the health of vital pulps. The
color is an objection in anterior positions, and the process of build-
ing a filling is comparatively slow and taxing on patient and
operator.
Welding of Gold. Gold welds cold when properly prepared, is
absolutely pure, and the contacting surfaces are clean. Any alloy
in its substance (excepting platinum) or foreign substance upon
its surface totally destroys this quality, until such substances
are removed, when the property of welding cold again returns.
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