Page 18 - My FlipBook

body can be fused on pure gold, provided enough time is given. Some
low fusing porcelain will fuse above the fusing point of pure gold, pro-
vided the requisite heat to fuse the gold is obtained rapidly. While the
above distinction seems to meet all practical requirements, it is un-
scientific and its only value is to make a convenient distinction between
the two classes of porcelain for practical usage.
Because porcelain is an indefinite compound and has no definite
fusing point, the following distinction is made between high and low
fusing porcelain. High fusing porcelains require more than five minutes
to fuse, while low fusing porcelains require less than five minutes to
fuse at 2,000 degrees F. It is impossible to fuse any of the high fusing
porcelains at 2,000 degrees F. in five minutes, and it is also impossible
to keep any of the low fusing porcelains in contact with a heat of 2,000
degrees F. for five minutes without becoming over fused. Porcelains
are divided into basal bodies, foundation bodies, enamel bodies and
glazes. All basal and foundation bodies are high fusing porcelains,
while enamel bodies and glazes may be either high or low fusing por-
celain.
Basal bodies are used in crown and bridge-work and for the con-
struction of hand carved teeth, but there is no necessity for using them
in inlay work. The use of basal bodies requires a specially constructed
furnace for obtaining and maintaining the intense heat needed to fuse
them. The present types of electric furnaces may be used, but they can
not be depended upon to furnish enough heat to fuse large masses of
basal body unless new muffles are procured oftener than most dentists care
to buy them, because the intense heat causes the fire clay readily to affect
the platinum wire of the muffle. But the foundation and enamel bodies
will meet the requirements for inlay work, and the operator should learn
the characteristic properties of each of these two classes of porcelain.
While all the porcelains have properties in common, there are, how-
ever, certain properties which characterize each manufacturer's product.
It is important that these characteristics should be thoroughly under-
stood in order to obtain the best results. With all porcelains the general
principles of manipulation are the same. All may be mixed with alcohol,
but this mixture is not adapted to molding and carving. Likewise all
porcelains may be mixed with water, which insures the possibility of
molding and carving.
Laboratory experiments with the various porcelains will prove of
great value both to the student and the practitioner. If the characteristic
properties of the different porcelains are understood, the selection of
the material to meet individual requirements will be simplified and the
operator will be relieved of much uneasiness.

14