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EXCAVATION OF CAVITIES BY CLASSES. 67

the disto-lingual groove to the crest of the hngual marginal ridge,
and frequently to follow it over onto the lingual surface of the
tooth. This should be done with the inverted cone bur, as
previously described (pages 35 and 62).
In the lower molars the grooves are generally deeper and
more deeply sulcate than in the uppers, and will much oftener
require cutting out to the crests of the marginal ridges. These
teeth frequently have a lingual inclination, which renders occlusal
cavities less easy of approach. In this they present great varia-
tion, many being as easy of approach as the upper teeth, and
sometimes easier. Yet frequently there occurs a lingual inclina-
tion that renders them very difficult. If these are prepared for
filling with gold by the use of direct force, the mesial wall must
be inclined to the mesial, and the mesial portion of the buccal
wall must be strongly inclined to the buccal to allow of direct
force being used. It is in these cases, however, that reverse
pluggers have their greatest use, and when such cavities are to
be prepared for the use of these, the mesial and buccal walls may
be squared up in the axial plane ''^ without inclination by use of
the. square-ended fissure bur in the right-angle hand-piece, or
with hoes 12-5- 12 and 12-5-23, and the binangle chisels. Gold
can then be well packed with reverse pluggers, but not by direct
force.
Occlusal cavities in the upper bicuspids are so easy
and direct of access, that little difficulty is experienced in their
preparation. The principal points of instrumentation are the
same as have been described.
Occlusal cavities in the lower bicuspids are difficult
only in cases of strong lingual and distal inclination of these
teeth. In these cases the instrumentation is similar to that
described for the second and third lower molars, except that
smaller cutting instruments will be required.
Pit cavities in the buccal surfaces of the molars.— The
pit cavities in the buccal surfaces of the molars must be distin-
guished sharply from smooth-surface cavities occurring in these
surfaces. The pit cavities have their beginning only in the
buccal pits and arc primarily in the occlusal half of the buccal
surface. .Smooth-surface buccal cavities are primarily in the
gingival half of the buccal surface and begin in the smooth
* Any plane, one direction of which is parallel with the long axis of the tooth.