Page 269 - My FlipBook

CAVITY PREPAEATION. 115 ;

Finish of enamel, wall. Finishing the enamel wall and
beveling the cavo-surface angle is the last cutting done in the
pi-eparation of a cavity. This should always be done with the
rubber dam in place and with all provisions made for the imme-
diate 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 i)ractieable 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 slight 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 lia-
bility. But the marginal angle of the filling material which
covers the bevel must not be made too thin by too great a bevel
of the cavo-surface 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.
Toilet of cavity. This is the final step in cavity preparation
and consists in freeing all surfaces from chips and dust that
have accumulated during the excavation. The bulk of this is
done, of course, with water or the chip blower during the prog-
ress of the excavating. But there will remain some fine dust
upon the walls and margins that can not be removed in this way.
It is not well to wash this with any known liquid, for, even with
the use of pure alcohol and after drying with the air syringe,
something will be left coating the walls. The best thing yet
devised is thorough wiping, or sweeping, of all parts of the cavity