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204 THE TECHNICAL PROCEDUBES IN FILLING TEETH.

little distance with a flat burnisher so that one of the special
clamps, Figure 90, can be placed to the gingival of the decayed
area, the i^reparation of the cavity may be made at once. In
any such case, the special clamp should be put on before the rub-
ber is placed, in order to have nothing in the way of placing the
clamp just right. Then the rubber may be thrown over it.
(2.) The cavity may be roughly excavated without the rubber
dam and filled with a sufficient ball of softened base plate gutta-
percha, to hold the gum away and cause its absorption within
a few days. (3.) The overlapping gum may be cut away at once,
and the operation proceed. Those who have learned to handle
the actual cautery well may do this best with a white-hot bur-
nisher. A fairly quick stroke of a white-hot instrument is prac-
tically painless and no bleeding follows it. An instriuuent at
a dull red heat burns fearfully and should never be used.
When this preparation is done and the clamp so placed as
to expose the gingival wall and surface of the tooth beyond the
cavity, the principal difficulty is ended. The undermined enamel
may be chipped away as far as desirable and the extensions
made, completing the outline form as shown in Figure 287. The
extension to the mesial and to the distal can each be made with
the bur, and chi])ping with the chisel, the operator generally
standing in the left side in front position with the patient's face
turned away to the right. Sometimes it will be more convenient
to make the extension distally with the end of the bur against
the distal wall, the operator standing on the right side behind
or the left side in front for the upper teeth of the left side, and
on the right side in front for the upper teeth of the right side.
With these instruments and these positions, such cavities are
not very difficult of preparation. Usually in large cavities, the
sensitiveness is much less than in the beginning decays shown
in the first molar and bicuspids of the same figure. The detail
of the outline form, except for the enlargements occluso-gingi-
vallj^ and of the retention form, is completed, as has been indi-
cated for other cavities of this class. Parallel occlusal and gingi-
val walls or some slight undercutting give sufficient retention
form. The finishing is done in the same manner as in other cavi-
ties. The toilet finally renders the cavity fit for the filling.
Variations. The forms of the cavities in the first molar and
bicuspids in this case are sufficiently shown in Figure 287. The
instrumentation should be in no wise different from that given
for the series of illustrations 283, 284, 285, and need not be
repeated. The Hatch clamp should be used to hold the rubber