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EXCLUSION OF MOISTURE 191

method the operator will soon become familiar with the location in
each case.
The Number of Teeth Isolated depends upon the location and the
operation to be performed. For the short treatment cases, sometimes
the placing of one or two teeth under the dam will suffice, but in
most eases where fillings are to be made and polished, from five to
eight teeth should be included that a good view of the field of opera-
tion may be had and the loose folds of dam carried farther away to
avoid them catching in the revolving points of the engine.
With Anterior Teeth the first bicuspid tooth of either side should
be included, as the cuspid from its conical shai)e is many times
unsafe for a final ligature.
With Bicuspids and Molars as the objective teeth in an opera-
tion, there should also be included the teeth anterior to the median
line.
The Clamp should be placed on the tooth back of the one to be
operated upon, excepting in mesial cavities in second molars when
the clamp may be placed on the second molar, thereby avoiding the
clamping of the third molar except when absolutely necessary, as
with distal cavities in second molars.
The Placing of the Dam requires the freedom of both hands of
the operator, and the aid of an assistant is of value. The necks of
the teeth upon which the rubber dam is to be placed should be cleansed
of all calculus and sordes and flooded with a jet of water from the
syringe. If the gums show hypersensitiveness they should be bathed
in a solution of novocain, restricting its use to the gingival borders.
Waxed silk should be passed through the proximal spaces to clean
them and prove access for the rubber. If sharp margins of ca\^ties
cut the silk these should be dulled by passing a thin ribbon saw
through the proximal space or, with the chisel, carry the margin
sufficiently into the embrasure to give access.
When teeth are in close contact so that the silk thread is passed
with difficulty, the rubber can be made to pass more readily by tho
use of soap, which is done by placing the row of holes on the ball
of the index finger, occlusal side up, and rubbing the soaped fingers
of the other hand across the holes.
The Occlusal Side of the Rubber Dam is that side Avhich is to-
wnrd the occlusal surface when the dam is in position.
The Gingival Side is the opposite side and is next to the gingival
margins when the dam has been applied to the teeth.
The Method of Applying the Dam is affected by the fact of