Page 124 - My FlipBook

120 OPERATIVE DENTISTRY
submerged in much the same way as a tooth is invested to have a
backing flowed but sufficiently deep upon the wax sprue former to
leave upon its removal a receptacle for the gold solder to be fused.
Saturating the Model. Heat may be applied to the invested pat-
tern as soon as the investment has set, and the wax gradually
burned out leaving a frame\\ork of pure gold filling the mold.
Then scraps of 22K gold plate are placed in the hole left by the
sprue former and all is heated to the point of fusing the 22K gold
which Avill disappear through the opening and completely saturate
the pure gold Avithin the mold. The inlay may be immediately
chilled and finished. This method has to recommend it, speed of
manipulation, and is indicated in large contour restorations, where
it is desired to use a solid inlay.
Making the Cast. Generally considered we have three forces
used in placing the gold in the mold; suction, pressure, and cen-
trifugal. Centrifugal force is the only one wherein all atoms or
molecules of the material are acted upon, and greater accuracy is
obtained by this method.
Place of Heating- the Gold. The temperature of the mold at the
time the gold strikes it, in casting, is of great importance. There-
fore, the place where the gold is melted should not be on the body
of the investment over the mold, for by that method we are not
able to vary the temperature of the mold at the time of casting.
The gold should be melted on a separate tray and the mold should
be heated to the desired temperature independently of the material
being east.
Temperature of the Mold. By a little experimenting we will be
a])le to demonstrate that a body of molten gold contracts toward,
first, that part which is chilled first, second toward the greatest
body of gold; that is, when the gold consists of two parts con-
nected by a small isthmus, or in other words, pedunculated, there
is a tendency for the smaller body of gold to shrink toward the
larger one. The first part of the gold which we desire to set
through the process of chilling is that part of the inlay which is
most essential to a perfect fit, namely the margin or that which
covers the marginal bevel and second all of the cavity walls.
Therefore, it is important when the gold is thrown into the mold
that the investment which forms the mold be of a temperature to
chill the gold at first impact, bearing in mind that it should be
Avarm enough to permit of the gold to enter the sharpest recesses.