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160 THE TECHNICAl. PEOCEDUEES IN FILLING TEETH.
188, first using chisel 10 or 15 with hand pressure, and later with
mallet strokes, chipijing from the more convenient points as the
work progresses. Mallet pressure is usually the hest after the
first few cuts. In the distal part of the cavity wall, it is often
best to reach across and use the pulling motion, so called, in
splitting away the overhanging enamel. This is illustrated in
Figure 189. The edge of the chisel is engaged close to the mar-
gin of the broken edge of the enamel, and, with a downward
pulling motion, chip after chip can be thrown off in rapid succes-
sion. This is continued in different directions until the cavity
of decay is uncovered, as shown in Figure 189. In this case the
two cavities are separated by a strong strip of enamel firmly
supported by sound dentin. This is difficult to remove with
chisels. For the removal of this, engage an inverted cone bur
10 in the dentin close against the dento-enamel junction and
force it in toward the line of the mesial groove and draw
it slowly to the surface of the enamel. Let the bur cool a
moment and then repeat the movement. Make cut after cut,
following tlie mesial groove — the weakest line in the enamel
— until a slot is cut uniting the two cavities. Now run the
bur along this slot, pressing first to the buccal and then to
the lingual. Figure 190, undermining the enamel as far as the
slope of the bur head will allow. Chip this undermined portion
away with enamel hatchets 15-8-12, or the corresponding width
chisels, as shown in Figure 191. Continue this by repeating the
undermining and chipping until the opening is as wide as may
be desired for the step. The bur, if carefully used, will have
made the pulpal wall of this portion flat. In making these cuts,
the bur may be entered in the pit cavity and the first cut made
toward the mesial cavity if that should seem the most convenient
in any particular case. The last of this cutting is shown in Fig-
ure 191.
Variation of proceditre when pulp exposure is feared.
At this point the question of the possible exposure of the pulp
will become important. Therefore, the enamel walls should be
trimmed with the enamel hatchets and chisels and the buccal
grooves cut out as in Figure 192, but not deeper at first than
the dento-enamel junction, particularly in the occlusal part of
the cavity. The walls of the mesial portion of the cavity should
be cut to sound dentin in every direction, using the enamel
hatchets, as shown in Figure 192. This will have completed
roughly the outline form, except the extension that may be neces-
sary in the mesial portion. At this point the rubber dam should