Page 89 - My FlipBook

ARTIFICIAL DENTURES. 77
sli(~>iikl the sand be used too dry, as in that case it will crum-
ble away in detaching- the plaster model.
Oil is being- used by some as a substitute for water
in molding. Sand, wdien mixed with oil, has the advantage
of always being in readiness for use. It should be used in
alxmt tlic proportion of one (juart of oil to a peck of sand.
Preparing the Plaster Cast for Molding.—After the cast
has been secured, the outline of the plate, and the position of
the vacuum-chamber and clasps, wdien used, should be dis-
tinctly marked with a pencil. In upper cases, whether par-
tial or full, a shallow groove should be made along the pos-
terior plate line, so that wdien the plate is swaged this edge
will press firmly against the roof of the mouth, wdiich will
add to the adhesion of the plate, make the edges less per-
ceptible to the tongue, and prevent the entrance of the secre-
tions and food. The cast should also be carved at the
points where the integument of the palate is soft and yield-
ing. In some cases, the center of the palatal portion of the
mouth is unusually hard and unyielding, in fact, large, bony
prominences are sometimes found ; these points should be
noted when the impression is taken ; then, before making the
die, a slight coating of w^ax should be placed over the cor-
responding parts of the cast, so as to relieve the pressure at
this point, which pressure w^ould otherwise cause rocking of
the plate, thus interfering wath its adhesion and the w^earer's
comfort.
Method of Making the Mold. —When the material has
been selected and prepared, and the model trimmed and
carved where needed, it should be given a coat of varnish
or oil, or, what is still better, covered with lycopodium and
then thoroughly brushed with a jeweler's brush or soft
brush-wheel ; it should then be placed face uppermost on the
molding board or table, and surrounded with a metallic
molding ring. The molding material should then be packed