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150 THE TECHNICAL PROCEDTXRES IN FILLING TEETH.

Outline of occlusal step. The next procedure is to cut
the outline of the step in the occlusal surface, as shown in Fig-
ures 167, 168. Select an inverted cone bur 10, and, placing its
shaft nearly or quite parallel with the long axis of the tooth,
enter the bur sidewise into the dentin just beneath the dento-
enamel junction and draw it slowly to the occlusal surface of the
enamel. Repeat this motion in cut after cut, following the mesial
groove distally to the pit in the central fossa. Then, with
straight chisel 15 or with the enamel hatchets 15-8-12, chip away
the enamel from either side of the slot formed by the bur. Pass
the bur along the slot again, first pressing it strongly to the
lingual, undermining the enamel in that direction and then to
the buccal, and again chip away the enamel both to the buccal
and to the lingual. Eepeat this until the step occui^ies the full
middle third of the occlusal surface bucco-lingually to and
including the pit in the central fossa. The buccal groove and
other sharp grooves should be cut out, as in the preparation of
occlusal cavities. This completes the outline form of the occlusal
portion.
In cutting the proximal portion to outline form, enamel
hatchets 15-8-12 should be used with a few strong, vigorous
strokes to trim the overhanging enamel from the buccal and
lingual walls. This cutting may often be done easily with the
straight and binangle chisels. Then sweep the enamel hatchets
around the gingival wall with a scraping motion, cutting to
sound dentin. Note particularly that the enamel hatchet of the
proper bevel to cut the lingual wall should cut to the lingual
in trimming the gingival wall ; while the one with the proper
bevel to cut the buccal wall should move to the buccal in cutting
the gingival wall. K the cavity is shallow mesio-distally, this
will incidentally remove most of the carious dentin; but that
is immaterial. If the cavity is very deep mesio-distally, no
further effort should be made at this time to remove the carious
dentin.
AVlien the buccal and lingual walls have been cut away to
sound dentin, it is often necessarj* to extend them farther. They
should be cut well into the embrasures, both buccally and lin-
gually, so that the cavity margin will be removed from near con-
tact with the proximating tooth. See Figure 167. The amount
of this cutting must be determined by the depth of the embra-
sures in each case. Wlicn much sound onanu'l must be removed,
it is easier to do it ])y inti'oducing an inverted cone bur 10 into
the dentin close against the dento-enamel junction, about the