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»» THE TECHNICAL PROCEDURES IN FILLING TEETH.

Next the proximate portion of the cavity must be extended.
When the buccal and lingual walls have been cut away to
sound dentin, it is often' necessary to extend them further.
They should be cut well into the embrasures, both buccally and
lingually, so that the cavity margin will be removed from near
contact with the proximating tooth. When much sound dentin
must be removed to accomplish this, it is easier to do it by intro-
ducing an inverted cone bur into the dentin against the dento-
enamel junction, about the bucco-lingual center of the length of
the gingival wall, and carry it buccally to the buccal wall, squar-
ing out the bucco-^ingival angle, and then, drawing it along the
buccal wall toward the occlusal surface, undermine the enamel
along this wall also. Then the undermined enamel is easily
cut away with the enamel hatchets, or by chipping with the
chisel used from the buccal angle of the tooth through the
embrasure. Cut out and extend the linguo-gingival angle and
the gingival wall in the same way and using the same instru-
ments. A good rule as to the extent of the extension is
to cut the lingual wall to a line where its margin will be
in view, past the proximating tooth when looking across
the central incisors at the median line, and make the
extension of the buccal wall to correspond. In some instances
it will be found that after this extension has been made, a line of
superficial injury to the enamel extends beyond the margin of
the cavity at one or both of its gingival angles. This should be
carefully looked for, and when found, the cavity should be fur-
ther extended so as to include the injured portion.
It must now be determined whether or not the gingival wall
has been sufficiently extended gingivally for its margin and its
buccal and lingual angles to be covered by the free margin
of the gums when the filling is finished. If not, it must be
extended further to the gingival. This is difficult to do entirely
with hand instruments, but by using an inverted cone bur with
its flat end against the gingival wall, it is inclined sufficiently for
its corner to engage, and carried, within the dentin, along the
dento-enamel junction to the bucco-gingival angle, then inclined
in the opposite direction it is carried into the linguo-gingival
angle. In this way the enamel to the gingival is undermined
and may be much weakened by passing the bur a few times with
hard pressure against its inner side. It may then be removed