They have a high thermal expansion.
They do not shrink unless used with solvent.
(3) They are radiopaque, conduct heat poorly, and are easy to remove from
the root canal.
(4) They may be kept sterile in antiseptic solution, are impervious to
moisture, and are bacteriostatic (prevent the growth or multiplication of bacteria).
They shrink when used with a solvent.
They are not always easy to introduce into the root canal.
a. General. Dental porcelain is manufactured as a powder. When it is heated
to a very high temperature in a special oven, it fuses into a homogeneous mass. The
heating process is called baking. Upon cooling, the mass is hard and dense. The
material is made in a variety of shades to closely match most tooth colors. Baked
porcelain has a translucency similar to that of dental enamel, so that porcelain crowns,
pontics, and inlays of highly pleasing appearance can be made. Ingredients of
porcelain include feldspar, kaolin, silica in the form of quartz, materials which act as
fluxes to lower the fusion point, metallic oxide, and binders. Porcelains are classified
into high-, medium-, and low-fusing groups, depending upon the temperature at which
fusion takes place.
b. High-Fusing Porcelains. High-fusing porcelains fuse at 2,400 Fahrenheit or
over. They are used for the fabrication of full porcelain crowns (jacket crowns).
c. Medium-Fusing Porcelains. Medium-fusing porcelains fuse between 2,000
and 2,400 Fahrenheit. They are used in the fabrication of inlays, crowns, facings, and
pontics. A pontic is the portion of a fixed partial denture, which replaces a missing
d. Low-Fusing Porcelains. Low-fusing porcelains fuse between 1,600 and
2,000 Fahrenheit. They are used primarily to correct or modify the contours of
previously baked high- or medium-fusing porcelain restorations.