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34 THE TIGHTENING OF LOOSE TEETH

Thin platinum wire must be used. Iron wire may
cause much trouble by rendering the platinum-gold
wire friable by oxidation. Now the teeth should be
removed from the pins (see Fig. 24).
All the parts, except the ends of the wire splint
that are to be soldered, should be covered with Paris
red, and splint and abutments soldered together very
strongly on the plaster model.
This is necessary, as weak soldering cannot offer
sufficient resistance to the biting strain, and as,
further, the collar of an abutment might tear away
at such a place.
The collar must therefore be strengthened by
adding thin metal at this place.
The bridge is boiled, carefully finished, and electro-
gilded. A plain bowl may be used, and a hot bath
prepared of 12 parts of cyanide of potassium solution
and 100 parts of water.
A small piece of pure gold or a coin is put on
the negative pole, and allowed to boil for ten minutes.
Then the object to be electrogilded is put on the
positive zinc pole, and kept immersed in the tluid for
some minutes.
After deposition has taken place, the object is
cleansed with a glass brush.
The bridge adapted and the teeth replaced on the
pins, the root surfaces should be smoothed with keen
sandpaper discs, in order to prevent them from irri-
tating the processus alveolaris.
Small bridges may be immediately cemented ou,