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SIMPLE CAVITIES ON EXPOSED SURFACES. 28i

ture, either in the form of blood or serum from the wounded gum or
mucus from the follicles situated along the mucous surface. Since the
introduction of the rubber dam this difficulty has been greatly modified.
But when the cavity extends somewhat above the nor-
Fig. 241.
mal gum line there is more or less difficulty in keeping
the rubber above the gingival border of the cavity. This
is best done by taking a straight instrument the point
of which has been made very sharp by rubbing it upon
an Arkansas hone. The dam is then raised well above
the cavity border and the jioint })ressed firmly into the
dentin and held with the left hand throughout the ope-
Woodward clamp.
ration of filling the cavity. A very neat and valuable
device in the form of a clamp has been introduced by Dr. W. A. Wood-
ward for this purpose. It is shown in Fig. 241.
The dam should include not only the tooth to be filled, but several on
each side of it. With the left hand it is stretched above the margin
of the cavity, w^hile with the right hand the two little points on the
bow of the clamp are pressed firmly into the cementum above the cavity.
The clamp is then made secure by turning the set-screw% This clamp
when well seated rarely fails, and the operator feels that this difficult
operation has become a simple one.
There are cases, however, where the decay has followed the receding
gum or extended beneath it to such an extent that the clamp cannot be
used. To overcome this difficulty the gum should be slit and a
" Mack " screw inserted to the depth of two or three threads into the
dentin. The rubber dam is then draw'n above this and held securely
above the cavity. When the operation is completed the screw should
be cut olf with the wedge-cutters and nicely smoothed. When the slit
in the gum has healed, the portion of the screw remaining will be
concealed.
Most cavities upon the labial surfaces are shallow and are best filled
with cohesive foil or Watts' crystal gold. It is well to fix the first piece
securely in a small retaining pit and build each piece
Fig. 242.
upon a sure foundation. As fillings upon the labial
surfaces of teeth are usually conspicuous (Fig- 242),
it is often desirable to fill such cavities with plat-
inous gold, because the tint of the two metals in
combination is more nearly the shade of the tooth.
Labial fillings.
Especially is this true in teeth of yellowish hue.
Class E.—As cavities upon the lingual surface of the incisors are
usually confined to the laterals and most frequently are the result of
imperfect development of the enamel in relation to the cingulum (see
Chapter I., p. 25) ; they are small in size and easily filled. A tape of