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CHAPTER XLII.
THE USE OF FUSED PORCELAIN IN FILLING TEETH.

Definition. A porcelain inlay is a filling made of dental porce-
lain and retained in position by cement.
A Dental Porcelain is a solidified mass of silicious substances
suspended in a flux of fused silicate.
Composition. Dental porcelain is composed: First, of the basal
ingredients which are refractory, as silex, kaolin, and feldspar. Sec-
ond, fluxes used to increase the fusibility. Those in common use are
sodium borate, or borax, (Na2B407), sodium carbonate (NagCOa),
and potassium carbonate (K2C03). Third, metals and oxides used as
pigments.
Silex (SiOa) is the oxide of silicon. It is an infusible substance,
insoluble except in hydrofluoric acid and is used to give strength to
the porcelain. It gives it more translucent appearance.
Kaolin [Al4(Si04)3.4H20] is the silicate of aluminum. It is added
to the porcelain to give stability, and permits unfused porcelain to
be molded and carved in the shaping of the contour.
Feldspar [K20Al203(Si02)G] is the double silicate of aluminum
and potassium. It forms over eighty per cent of the basal mass of
porcelain and adds translucency.
Pigments. The various shades and colors in porcelain are pro-
duced by the addition of precipitated gold, platinum, purple of
cassius, oxides of cobalt, titanium, iron, uranium and silver, pro-
ducing the colors of red, yelloAV, blue, green, broAvn and gray.
High-Fusing Porcelain. By high-fusing porcelain is meant a
porcelain that requires five minutes or more to fuse at a tempera-
ture exceeding the fusing point of pure gold.
Low-Fusing Porcelain. This is a porcelain that requires less than
five minutes to fuse at a temperature not exceeding the fusing
point of pure gold. This division is one of creation by the manu-
facturers and commonly accepted by the profession. However the
distinction is only relative as porcelain has no definite fusing point,
as any enamel or tooth foundation body may be fused on a matrix
of pure gold if enough time is given to the fusing process.
Effects of Fusing at Lower Temperatures and a Longer Time.
A more homogeneous mass is produced.
A more characteristic color is maintained.
A less friable filling is produced.
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