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178 MECHANICAL DENTISTRY AND METALLURGY.

proportion of two parts of plaster to three parts silex. and
fill the band with the investment, building up slightly around
the post. After investment sets, boil out the wax. Fig.
148 shows the tooth w^ith investment in band and wax
removed.
Applying the Body.—Back up with porcelain body and
put in the furnace and fuse. Add more body, building up
over anterior surface of band to conceal it. and fuse again.
We now have a finished crown, as shown in Fig. 149.
In baking, the crown is placed in a small tray or slide,
as shown in Fig. 150, putting post through a hole in back
end of tray, face up. This prevents the tooth being fused
Fig. 148. Fig. 149. Fig. 150.

on to the tray, as it rests only on the back of the band, being
held up by the post, and the body not being built up over
the posterior part of band.
Ordinary teeth for vulcanite work can be used in making
this crown if desired. When they are used the post should
be soldered between pins with pure gold.

THE MASON CROWN.
It has long been the desire of the profession to overcome
the annoyance caused by the breakage of the porcelain
facings in crown- and bridge-work. Many efforts have
been made to produce detachable facings, but prior to the
introduction of the ]\Iason crown none has l)een designed
that could be manufactured and sold to the dentist for- his
immediate use. Through the efforts of Dr. W. L. Mason,