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78 THE TECHNICAL PROCEDURES IN FILLING TEETH.

edge will not be thrust into the depths of the cavity and cause
pain. Continue this cutting until the enamel is found supported
by sound dentin, or until the cavity of decay is well exposed.
In many cases it will be best in this position, when decay is
extensive, to leave some enamel unsupported by dentin, espe-
cially when of about full strength, rather than expose so much
filling material as the complete removal of the enamel would do.
When this wall has been chipped away sufficiently, chip away
the lingual wall in the same way and with the same instrument,
working from the lingual. This, if the cavity be not very small,
will give good access to all of its parts. If the cavity is small,
take hatchet 8-3-12 and introduce its blade between the teeth
from the labial, with the edge directed to the gingival, catch the
enamel near the cavity margin and chip it away by a prying
motion, using the proximating tooth as a fulcrum, removing as
much enamel in this way as practicable. Only the thinner por-
tions of weakened enamel margins can be removed by this
motion ; but now a stronger instrument may be used, sufficient
room having been obtained for its introduction. Generally,
hatchet 12-5-6 or chisel 10 may be introduced against the labial
enamel wall, with its edge directed toward the gingival and the
enamel wall trimmed away, using strong hand pressure, and, by
changing the direction, the cutting can be continued along the
gingival wall to or past the labio-lingual center of the tooth.
With the same instruments working from the lingual, the lingual
wall is next cut down in the same way, to, and somewhat past,
the linguo-gingival angle of the cavity. For trimming the
remainder of the gingival wall hoe 12-5-6 will be required, or
the 8-3-6 if the cavity is not opened sufficiently to admit the
larger instrument. This is done with a scraping motion. Fre-
quently hatchet 12-5- 12 will do this well, working from the
labial. The gingival wall should be cut to sound dentin and
made as nearly flat in the horizontal plane as practicable.
Now, examine carefully as to the requirements of extension
for prevention. In most cases a line of superficial injury to the
enamel will be found running away labially, from the labio-gin-
gival angle of the cavity near the gum line. Another line of
superficial injury leads away in similar fashion from the linguo-
gingival angle. Often, also, particularly in the smaller cavities,
there is superficial enamel injury to the gingival of the gingival