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148 THE TECHNICAL PROCEDURES IN FILLING TEETH.
the lingual at a considerable inclination, and it is now necessary
to make the opening as near parallel with the length of the pulp
canal as practicable. To do this use a fissure bur, pass its end
into the pulp chamber and bring the hand-piece slowly parallel
with the long axis of the tooth, cutting mostly from the incisal
wall of the opening first made, but also cutting some from the
distal wall of the pulp chamber. This cutting should be suf-
ficient to admit a broach to the full length of the canal, with
very little bending. The cleaning and treatment of the canal
can then be proceeded with.
Generally, when incisors have proximate fillings that are
good, the opening into the pulp should be made from the lin-
gual, without disturbing the fillings. If, however, there is reason
for removing a proximate filling, the pulp chamber should be
opened through the cavity.
In case of bicuspids and molars the opening should be
made through the occlusal surface. In bicuspids the mesial pit
should be chosen. In molars it is generally much easier to
penetrate the enamel through the pit in the central fossa. In
this case, as soon as the dentin has been entered, it is best to
introduce a small inverted cone bur, and cut a slot to the mesial,
inclining to the buccal, as far as the mesial marginal ridge, and
chip the enamel from its margins. The length of this toward
the mesial will depend on the position of the tooth and the incli-
nation of the hand-piece in drilling through the dentin. The
dentin is thick, and in passing through it, this inclination will
often carry the hole considerably to the distal. Therefore, in
beginning again with the drill it should be set sufficiently to the
mesial so that it will strike the pulp chamber centrally, or to the
mesial of its center. In drilling through the dentin the small
drill (one millimeter in diameter) should first be made to pene-
trate a little, and then the hole enlarged, then drilled deeper and
enlarged, until the dentin has been cut through. If the pulp is
alive and sensitive, it should now be destroyed ; if dead, the
opening may at once be so enlarged as to remove the entire
roof of the pulp chamber, and the treatment of the canals pro-
ceeded with. Never undertake to treat pulp canals through a
little bit of an opening.
In a considerable number of cases it is necessary to open the
pulp chambers of bicuspid and molar teeth that have been filled.