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42 THE TECHNICAL PROCEDURES IN FILLING TEETH.

in the upper teeth a considerable portion of the work may often
be done before applying the rubber dam, but it should always be
in place before the excavation is finished, and remain until after
the filling is completed. The rule should be that the walls of a
cavity should never become damp after the last of the cutting is
done in their preparation.
If, however, it appears from the position of the tooth, and
the conditions present, that the field of operation will be contin-
ually overflowed by saliva, or that the case
is particularly diffi-
cult to see, the rubber dam should be placed before beginning
the operation. In proximate cavities it is generally best to open
the cavity by cutting away the overhanging enamel, and to deter-
mine the position of the gingival wall of the prepared cavity with
some degree of certainty before applying the rubber dam. This
will usually facilitate the' application of it, and in obtaining
its
proper position in relation to the gingival wall.
Preparations for Applying the Rubber Dam.

The rubber dam should be tough and very elastic. Gener-
ally a medium thickness should be employed. It should be cut
in pieces about six inches square. Before making any effort to
apply it, the teeth should be well cleaned and douched with a
stream of warm water from the syringe to free them from gummy
material, and from collections of micro-organisms that would
otherwise be forced under the free margins of the gums, or even
into the soft tissues, by the ligatures or clamps. The interproxi-
mate space should be cleaned by use of the ligature passed
between the contact points. In doing this the difficulties to be
met with in passing the rubber between the teeth will be deter-
mined. The position and size of the holes in the dam should
next be determined, together with the number of teeth to be
included. Not less than three, generally four or five teethi
should be included. If a front tooth is to be filled, include four
or more, always one or two on either side of the tooth to be
operated upon if a bicuspid or first molar, include one tooth
;
to the distal, and at least two to the mesial if the second molar
;
and the cavity involves the distal surface, include the third
molar the
; if the cavity does not involve the distal surface,
inconvenience of placing the rubber upon the third molar will
be greater in many cases than to do the operation with a clamp