Page 27 - My FlipBook

CAVITY PREPARATION. 23

with spoon excavator 20-9-12, laying the pulp bare. If this is
properly done very little pain is induced.
Finishing the enamel ^vall and beveling the cavo-sur-
face angle of the enamel is the last cutting done in the prepara-
tion of a cavity. This should always be done with the rubber
dam in place and with all provisions made for the immediate
placing of the filling material.
The cavo-surface angle of the cavity in every part of its
outline should receive especial attention. The plane of the
enamel wall should be as nearly as practicable in the line of the
length of the enamel rods, or such as will certainly cut more
from the outer than the inner ends of the rods, and should be
made smooth by a light planing motion of a sharp chisel or
enamel hatchet, the motion being in line with the length of the
margin. When this has been satisfactorily accomplished the
cavo-surface angle of the enamel should be cut to a distinct bevel
outward, also by a planing motion of the chisel, enamel hatchet or
the gingival margin trimmer, used very lightly. The depth of
this bevel should generally not include more than one-fourth the
thickness of the enamel wall. The angle of the bevel should be
from six to ten centigrades from the plane of the enamel wall.
The object is, first, to cut away any loose ends of enamel rods
that might afterward fall away and render the margin imperfect
;
and, secondly, to strengthen the cavo-surface angle of the enamel
as a safeguard against possible checking in packing the filling
material.
In this last work, two things should be held closely in view.
The cavo-surface angle of the enamel is friable and readily
broken by violence, and beveling will materially lessen this
liability. But the marginal angle of the filling material which
covers the bevel must not be made too thin by too great a be\el
of the cavo-surfiice angle of the enamel. If so, it will have no
strength and will tend to roughen and in this way render the
margin imperfect. Therefore, the bevel of the cavo-surface
angle of the enamel must not be too great.
Finally, the toilet of the cavity is to be made. This con-
sists in freeing all of its surfaces from the chips and dust that
have accumulated during the excavation. The bulk of this is
done, of course, with the chip blower during the progress of the
excavating. But there will remain some fine dust upon the