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O.\' } THOSPHA TES IX COMBIXA TIOX U 'ITII GOLD. 1 47

Whilst I prefer gold for all four of these crown contours, amalgam
may be used with success. The dam should be placed, the cavity
being shaped the same as where gold is to be depended upon. The
amalgam is then packed thoroughly into all undercuts and retainers,
being forced into them with balls of bibulous paper as has been
described. Supposing that all four cusps were to be restored, thus
choosing the filling of the greatest magnitude, in this class, the
amalgam should not be mixed too dry. There should be sufficient
plasticity to last during the packing without danger of fracture, or
flaking off. The full contour would be restored, the top of the filling
appearing convex. The next step is to hasten the setting of the mass
by the addition of gold foil, as described in connection with the use
of amalgam. The foil is cut or torn into small pieces, preferably as
thin as No. 3 foil, and a single piece laid over the amalgam. This is
then burnished into the with a smooth warm burnisher, and
filling
becomes incorporated with it. This is continued until it is found that
the amalgam is hardening. Then the contour may be perfected by
carving gently with a right-angled spatulate burnisher. The burnish-*
ing of gold is then continued, smaller ball burnishers carrying the foil
into the depressions which have been carved out, and rounding and
perfecting the lines. This is kept up till the filling is set enough to
be dismissed in safety, at which time it will usually appear to be a
the final of their color. This, how-
gold filling, pieces gold retaining
ever, is lost in the subsequent crystallization, so that when seen at the
next sitting the usual amalgam color is presented, save perhaps in
spots. A peculiar squeaking sound as the burnisher passes over the
that the mass has to harden.
surface will admonish the operator begun
If the after setting be thoroughly polished, it will appear very
filling
handsome, and will prove a good and durable piece of work.
crown cavities, where the
I must refer to the large cusps are intact,
but where the cavity itself is so large that further extension in any
direction, either for starting-point or for retention, would so weaken
the wall as to make subsequent fracture a probability. It is evident
once we it in, but
enough that such a cavity will retain the filling get
how shall we accomplish this with gold ? It is in this class of cases
that the oxyphosphate method is found most satisfactory. I promised
to explain this in more detail, and will do so here. After the removal
of all decay, the dam of course being in place, mix oxyphosphate to
a sticky consistency, and place it in the bottom of the cavity. Whilst
of gold foil loosely
still plastic, press into it two or three large pellets
let the whole rest till the cement sets
rolled, and without condensing
hard. We then have such an appearance as is shown by Fig. 167.
In this illustration, a represents the oxyphosphate, which it is observed
has been squeezed out over the borders, c, c, whilst b shows the