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EXCAVATION OF CAVITIES BY CLASSES. 149

the enamel rods in a small V-sliaped space. Remove this and
continue this, picking out tlie enamel little by little until the cav-
ity of decay is reached and uncovered. As soon as a break has
been made for a starting jioint, a bi beveled drill in the engine
may be made to penetrate to the dentin. Then the cut into the
cavity may be made with the inverted cone bur. After enlarg-
ing this Oldening by chipping from either side, uncovering the
carious cavity, the bur may be engaged in the dentin close to
the dento-enamel junction and by pressing it distally along the
line of the mesial groove and drawing it slowly to the surface,
cut after cut may be made until the central pit is reached.
The third plan is to place a separator in position for a
moment, lifting the teeth apart sufficiently to permit the use
of chisel 10, or a smaller width hoe of 6 angle, approaching the
cavity from the buccal direction. The instrument may be used
first to chip off small flakes of enamel from the buccal direction
and its position gradually shifted more and more to the occlusal
as the enamel is chipped away closer to the marginal ridge, until
finally the enamel of the ridge itself may be chipped away with
the instrument held in the occlusal direction. In cases in which
the separator has been placed in order to determine the presence
of the decay, the enamel may be broken away by this procedure
at the time. An inverted cone bur may then be used for continu-
ing the undermining of the occlusal enamel, as mentioned above.
Either form of this cut should ordinarily be made in a few
moments, after a little experience.
If considerable burrowing of decay in the dentin has
occurred, undermining the enamel, these first cuts with the chisel
are very easily made and the use of the drill is unnecessary.
This will open the way to chip off the enamel forming the mar-
ginal ridge with the length of the edge of the chisel placed mesio-
distally, first toward the buccal and then toward the lingual, and
continue removing the marginal ridge until the enamel is found
supported by sound dentin to both the buccal and the lingual.
In the cutting, especially if done by hand pressure, the edge
of the chisel should be set very close to the margin to be chipped
and the enamel cleaved off in little flakes, the direction of the
pressure and the motion being almost in the line of the length of
the enamel rods, but slightly inclined in a direction to throw
the chips oft' from the free surface into the cavity. The instru-
ment must be very sharp to be effective. The enamel should
T)e cut away toward the central fossa, as far as it can well be
done by the chisel.