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THR RUBBEK DAM. 83

the foot of the clamp. Then the left forefinger is brought across
the arch onto the ligature, which is finally placed by the right
hand between the thural) and forefinger of the left and so both
ends are held. Then the instrument is used by the right hand
as related above and the ligature slackened or tightened with the
left as required, until it is brought into position to enter between
the teeth. Or the ligature may be passed through the bow of the
clamp and held against the foot of the clamp on the lingual and
strongly pulled into the lingual side of the contact so that it will
be held in position. The other end of the ligature may then be
passed back through the bow of the clamp and the contact fully
passed.
When necessary to secure the rubber dam for the removal
of the clamp to place a separator, it is good policy to tie a small
bead to the ligature and pull this close into the buccal embrasure
before making the knot in the ligature securing it to the tooth.
This will secure the rubber dam much more firmly against being
pulled away in removing the clamp and substituting the sepa-
rator. In the absence of a bead, a hard pellet of cotton may be
tied into the ligature by several knots ; this will do quite as well.
It is often well to use these beads or knots to the distal of the
distal tooth exposed if for any reason a clamp is not to be used
or changes are to be made. It secures the rubber very firmly.
Applying the rubber dam over the special glamp. Another
method of avoiding the most serious difficulty in passing liga-
tures to force the rubber between teeth far back in the mouth,
is to set a special clamp (Figure 90, rights and lefts) on the tooth
first, and then throw the rubber over the bow of the clamp. For
this purpose, the fifth grasp should be used, and the hole in the
rubber should be a little larger than usual. The ends of the fore-
fingers should be placed fully to the distal side of the hole, or
so that its distal edge is fully between the finger ends and upon
their palmer surfaces. Then it must be so stretched that the
distal edge of the hole may be passed over the distal edge of the
bow of the clamp. Figures 80, 81, starting it first over its lingual
portion, bringing the lingual finger under the lingual side of
the clamp and sweeping the other finger around over the buccal
portion, bringing the fingers down against the outer margins of
the jaws of the clamp. Figure 82. Then release the grasp on the
rubber, and, by a little careful motion of the fingers, it is allowed
to close around the tooth under the clamp, Figure 83. The pass-
ing of the rubber over the clamp should be done entirely by the
sense of touch, and should first be practiced out of the mouth for