Page 284 - My FlipBook

126 THE TECHNICAL PROCEDURES IN FILLING TEETH.

with a few vigorous strokes, loosening up and partially remov-
Lng the softened material, and see whether or not there are some
points at which decay extends beneath the enamel. This is
readily determined by placing the edge of the hatchet under any
suspected overhanging enamel and pulling toward the occlusal.
The edge will be held if there is any overhang, and the depth to
which the blade has entered will indicate its extent. If such an
overhang is found, chip the enamel away and perfect this part
of the cavity outline. At this point, any grooves entering the
cavity that will interfere with a perfectly smooth finish of the
surface of the filling should be cut out as far as necessary on
the same plan as that described for the small pit cavity, using
the smaller fissure bur 8 or 10, and chipping away the overhang-
ing enamel sufficiently so that all sharpness of the grooves may
be made smooth in finishing the filling.
Resistance form and retention form. The next step should
be to square up the dentin walls. If there is a considerable mass
of decay obscuring the cavity, it may be first removed roughly
by a few vigorous strokes with spoons 20-9-12 or 15-8-12. In
squaring up the dentin walls, an inverted cone bur or a square-
end fissure bur 12 should be used. The fissure bur may be used
in cases in which it may be brought parallel, or nearly parallel,
with the long axis of the tooth, which can generally be done in
the occlusal cavities in the upper first molars and bicuspids.
This is i^laced with its end uj^on the pulpal wall, and, while rotat-
ing, pressed laterally against one of the surrounding walls and
carried around the whole cavity in a series of cuts. In all deep
cavities this must be modified to avoid cutting the recessional
lines of the ]3ulpal horns and thus avoid the possibility of expos-
ing the pul]), as will be explained later. This will s([uare up the
surrounding dentin walls and the square end of the bur will leave
the pulpal wall flat and its angles with the surrounding walls
sharp and definite. The flat pulpal wall completes the resistance
form, and if the dentin walls are cut parallel with each other
in some considerable part, that will be sufficient retention form.
It is necessary, however, to have these points distinctly in mind
in each case. This is to be taken as the plan of squaring up the
surrounding and pulpal walls (and axial walls in buccal and
labial cavities) when burs are used for tliat puri)ose. But burs
should not be used in this way in such positions as will endanger
the pulp of a tooth. This use of the bur should be in the smaller
cavities only, or only in particular parts of the larger cavities.
Care should be had not to continue any single cut so long as to