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EXCAVATION OF CAVITIES BY CLASSES. 91

distal cavity has been entered.
This slot may then be broad-
ened to the buccal and to the lingual in the usual way to form
the step.
The approach to distal cavities in the upper second molars is
often somewhat from the buccal, and to facilitate this approach
in building the filling the buccal wall should be strongly inclined
to the buccal, whenever this can be done without very positive
detriment to the case.
One should never neglect to obtain such
form as will render the filling of the cavity convenient.
In the lower molars, especially those that have a strong
lin-
gual inclination, the form of the distal cavity may be made for
filling with reverse pluggers. In this case the buccal wall may
be cut parallel with the long axis of the tooth and the gold
packed against it entirely with the reverse plugger.
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 right-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 these 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 instruments.
It will then be found that the cavity is easily reached with hand-
cutting instruments and the right-angle hand-piece, and is
readily filled with reverse pluggers after having attained facility
m their use.
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-buccal angle
of the tooth should be boldly cut away sufficiently to give access
to the gingival wall and the greater part of the cavity walls gen-
erally, and the step carried close against the mesial marginal
ridge.
This will allow a direct approach from the disto-buccal
to all of the cavity walls except the axio-bucco-gingival angle,
which must be filled by hand pressure.