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EXCAVATION OP CAVITIES BY CLASSES. 157

form to assist a little in holding the buccal and lingual margins
of the filling sufficiently away from near contact with the first
molai', that these may be kept well cleaned by the excursions of
food through the embasures. The management of this latter
feature in the treatment of both bicuspid and molar cavities
will be treated in more detail later.
The greatest difficulty is met with in distal cavities in lower
bicuspids that have a strong distal and lingual inclination. It
is in these that a contra-angle hand-piece and the reverse
pluggers are most needed. These teeth are often small and the
crowns long and decayed far to the gingival. They are difficult
to reach with direct instruments. In such cases, at least two
teeth to the distal should be included in the rubber dam. Even
if the first and second molars are lost, the rubber should include
the third molar to give good room for the use of the mouth
mirror for light and to hold the rubber out of the way of instru-
ments. It will then be found that the cavity is easily reached
with hand-cutting instruments and the contra-angle hand-piece,
and is readily filled by using the reverse pluggers. In the absence
of reverse pluggers, much of the filling must be made by hand
pressure. The form of the cavity should not differ materially
from the forms produced in other teeth. If, however, it is
decided that direct mallet force is to be employed to the greatest
possible extent, the disto-buecal angle of the tooth should be cut
boldly away sufficiently to give access to the gingival wall, and the
greater part of the cavity walls generally, and the step carried
close against the mesial marginal ridge. This will allow a direct
approach from the disto-buccal direction to all of the cavity
walls, except the axio-bucco-gingival angle, which must be filled
by hand pressure.
Relation of cavity walls to recessional lines of pulpal
HORNS. If a careful study is made of the forms and extent of
cavities permissible without cutting the recessional lines of the
pulpal horns, it will be found that there is generally sufficient
room between the recessional lines to make fillings with ample
strength. The point that is most likely to give difficulty occurs
in the lower first molars where broad mesial decays occur dur-
ing the childhood period, i. e., before fifteeen years of age. In
these it will sometimes be difficult to obtain sufficient width
between the recessional lines of the mesio-buccal and the mesio-
lingual horns of the pulp, combined with a proper depth over
the mesial marginal crest of the pulp to give enough strength
to sustain the broad mesial portion of the filling. This will be