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l8o MECHANICAL DENTISTRY AND METALLURGY. —

as quickly as desired. After removing from investment,
the groove should be thoroughly cleansed and dried ; also
the dovetail in porcelain. Now take some chlora-percha,
quite thick, fill up groove, and press porcelain home. Saw
off (never cut) the extended portion of metal dovetail and
finish as usual. Porcelain can also be cemented on with
cement or sulphur. For use as a dummy, articulate to
position, remove, and solder " stop " to neck of backing to
prevent porcelain from slipping upward ; replace on model,
join parts with wax, then withdraw the porcelain and invest.
The advantages gained by this method can only be appre-
ciated by practice. The first is that we do not, at any time,
ha\-e to place the teeth under the flame of the blowpipe;
second, we are not annoyed by the changing of color which
takes place in soldering; third, a solid backing, without
bubbles ; fourth, the invested piece can be cjuickly heated,
soldered, and cooled ; hfth, the small amount of solder neces-
sary — just enough *to join parts together; sixth, saving the
porcelain from being etched by borax ; seventh, we are able
to fit a bridge releasing the strain by cutting and resolder-
ing and not have the porcelain interfered with; eighth, the
most important of all, the amount of time saved to the busy
dentist in making repairs, it being accomplished in a few
minutes. The above is also applicable to the use of the
" Wedge-Lock " tooth in crown and bridge work.

THE ALL-GOLD CROWN, OR CAP.
In the construction of the all-gold crown, the sides of the
natural crown and neck of the tooth are brought down to
or a little smaller than—the size of the root. This is best
accomplished by the use of diamond discs and small car-
borundum-stones on the dental engine. From the occluding
surface, if any of it remains, a sufiicient amount should be
ground away, and the edges slightly rounded, to allow the
introduction of the gold cusps. The measurement and