Page 67 - My FlipBook

EXCAVATION OF CAVITIES BY CLASSES. G3

the mo\ement of the edge of the chisel should be in the direc-
tion of the length of the margin, or around the cavity. In such
a cavity as this, both the dentin and enamel walls may be per-
pendicular and the opposing walls parallel. The enamel rods
will be inclined toward the cavity in every part, and no outward
inclination of the enamel walls is necessary. The cavo-surface
angle of the entire margin should be slightly beveled to dirninish
the danger of fracture in placing the filling material. In such a
cavity no starting points for beginning the filling are required,
and no further preparation for retention of the filling is necessary,
except to see that the opposing walls are parallel.
Variations.— It will often happen that in a cavity of this
description a considerable area of decayed dentin will be found
beneath the enamel after the burs have been passed through into
In this case the overhanging enamel must be chipped away
it.
with hoe 12-5-6 or chisel 10 or 15, until sound dentin is reached
in every direction. When this has been done, the remaining
portion of the buccal groove should be cut out as described, first
completing the outline of the cavity. Then, if the area has
become considerable, the remaining decay is best removed with
spoons 1 5-8- 1 2 or 20-9-12, as may best suit the size of the cav-
ity. Enter the blade beneath the softened material, close against
the enamel wall at the lingual or buccal side, and force it with
a strong thrust in a curved direction to the other side of the
cavity ; two or three strokes well made should be sufficient.
Then square up the pulpal wall so that its angles with the sur-
rounding walls are sharp and definite, using hoe 12-5-6 or, in
some positions, hoe 1 2-5-1 2, with a scraping motion. In many
cases this will be as conveniently and accurately done with a
square-ended fissure bur, i /,? millimeters in diameter, or with the
inverted cone bur. In this use of the bur, the shaft should be
held parallel with the long axis of the tooth, so that the square
end of the bur will cut the pulpal wall of the cavity flat and
make its angles with the surrounding walls sharp and definite.
Finish the enamel wall and cavo-surface angle the same as before.
In many cases the mesial groove will be so sharp and deep that
it will require cutting out well toward the mesial marginal ridge.