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70 THE TECHNICAL PBOCEDUBES IN FILLING TEETH.

or less decay, with sliarp edges of broken enamel margins wliich
will cut the ligature, and which will be liable to cut the rubber
also. In any such case, the sharp edges should be found and so
cut away with a chisel that they will not interfere with the work
of placing the rubber dam. When this cleaning and examination
have been satisfactorily done, the parts should be flooded with
tepid water as the final step of the cleaning.
Peepabing the eubbek dam. Cut or select a suitable piece
of rubber dam for the case. If it is for the upper incisors, a
piece of the size and form shown in Figure 62 will answer.
There should be enough rubber above the holes to fully cover
the upper lip, but it should not cover the patient's nostrils.
Below the holes there should be enough to cover the lower lip
and chin. To the sides there should be enough to give good
room to place the rubber dam holders to stretch it back out
of the way. If, in any case, the part covering the upper lip
should be a little long and interfere with the breathing bj^ cover-
ing or partly covering the nostrils, it should be cut away with the
scissors.
The cutting of the holes for the teeth is done witli the
rubber dam punch. It is very important to have these in the
right position and the proper distance apart. The rubber should
generally be placed over two or more teeth to either side of the
one to be operated upon, if in the front of the mouth. If it is the
central incisor, the rule should be to expose the six front teeth.
If the tooth is to the side, an equal number of teeth to each side
should be exposed. If it is a bicusijid or molar, one tooth to the
distal and two or three to the mesial should be exposed. Special
conditions will often require deviations from these rules. In
individual cases there may be missing teeth, bridges, etc., that
will interfere and make something different necessary. The
cutting of the holes will depend in part upon conditions of inter-
ference with the ordinary rules of procedure.
When the holes have been cut and the rubber dam placed,
it should lay smoothly without wrinkles or drawing. The dis-
tance apart of the holes and their relation to each other, whether
in a curved line or otherwise, must depend upon the individual
case. For the incisors and cuspids in the normal arch, the holes
should be in an arc of a cii'cle somewhat larger tlian that
described l)y the arch, as shown in Figure 62. This will cause
that part of the rubber covering the roof of the mouth to be
loose and it will be apt to lay well up against the tissues out
of the way in doing any necessary work ii])on the lingual sur-