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FILLING MATERIALS. 673

Application of the Rubber Dam.—While many hesitate to attempt
the use of the rubber dam with children, it will be found upon trial that
most of them will submit to it without trouble, and many will prefer it
to other means of keeping cavities dry.
Although there is an advantage in applying the rubber dam before
excavating—because dryness makes the teeth less sensitive, and a clearer
view of the cavity is obtained—still, for the sake of not tiring the little
patients by too long restraint in one position, it is better to do most of
the excavating before its application.
The small size of the necks of the deciduous teeth compared with
that of the crowns renders the retention of the rubber dam easier than
with permanent teeth. Even considering the smallness of the patients'
mouths, the application of the rubber dam is not difficult in many
cases.
For retaining the rubber dam on the second molar a clamp will
sometimes be necessary, but for the other deciduous teeth a floss silk
ligature will be sufficient. Having punched holes of suitable size
through the rubber dam, apply it over the teeth aflected. If the cavity
is in the occlusal or buccal surface only, it will not be necessary to
apply it over more than one tooth, but if the cavity is in the approximal
surface it will be necessary to apply the rubber dam over two or some-
times three teeth, or even more, if several cavities are to be filled at one
sitting.
It is not always necessary to tie a ligature around the neck of the
tooth, as merely passing the waxed floss silk between the teeth will
often force the rubber around the neck of the tooth enough to retain it
even above an approximal cavity. The silk may then be removed by
drawing the end through between the teeth.
With a thin burnisher or spatula turn up the edge of the rubber
around the neck of the tooth toward the gum. The tendency of the
rubber then will be to slide in that direction and not off over the
crown. If a ligature be necessary to hold the rubber above the edge of
an approximal cavity tie it tightly around the neck of the tooth, even
forcing it toward or under the edge of the gum with an instrument when
necessary. The clamp on a second molar may often be dispensed with
after a ligature is applied, unless it is needed to hold the rubber out of
the operator's way. The only object in omitting the clamp is to pre-
vent pain or discomfort to the child.
If a simple ligature will not retain the rubber on a second molar
before the first permanent molar has appeared, its efficiency may be
greatly increased by stringing a bead, about an eighth of an inch or less
in diameter, on the thread and tying a simple knot in it so that the bead
will be in about the middle of the ligature. Tie the ligature around