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64 THE TECHNICAL PROCEDURES IN FILLING TEETH.

Pit Cavity in Central Fossa of Upper First Molar No. 2.
Description.— The pit is open so that the exploring instru-
ment readily passes in, giving room to be turned about, revealing
a considerable decayed area ; some discoloration shows through
the enamel.
Procedure.— Begin the excavation by chipping away the
overhanging enamel with straight chisel 15. Or, if the orifice
in the enamel is still very small, begin with straight chisel 10,
and use the 15 later. This may be done by hand pressure, but
mallet pressure is much better. Continue this chipping as far as
the enamel can be readily cut in this way, or until sound dentin
is found supporting the enamel at every point. Now look care-
fully to the relations of the outline of the cavity to the surface,
and proceed at once to cut out any grooves that will interfere
with a perfect finish of the filling. Now take hatchet 8-3-23, or,
if the opening into the cavity is too small for this, take hatchet
6-2-23, and sweep its edge around the dentin wall of the cavity
with a few vigorous strokes, loosening up and partially removing
the softened material from them, and see whether or not there are
some points at which decay extends beneath the enamel. If such
are found, clip the enamel from over them and perfect the cav-
ity outline. At this point the rubber dam should be adjusted.
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.
In squaring up the dentin walls a square-end fissure bur
(irV millimeters) may be used in cases in which this may be
brought parallel with the long axis of the tooth, which can gen-
erally be done in the occlusal cavities in the first molars and
bicuspids. This is placed with its end upon the pulpal wall,
and, while rotating, pressed laterally against one of the sur-
rounding walls, and carried around the whole cavity in a series
of cuts. This will square up the surrounding dentin walls to the
enamel walls, and its square end will leave the pulpal wall flat,
and its angles with the surrounding walls sharp and definite.
This is to be taken as the plan of squaring up the sur-
rounding and pulpal walls (and axial walls in buccal and
labial cavities) when burs are used for that purpose.