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86 THE TECHNICAL PROCEDURES IN FILLING TEETH.
more than usual attention should be given by the student to the
specific plans and details of these operations. The instruments
used are almost exclusively the specials. There is very little
that can be done advantageously with the ordinaries except
some occasional cutting with the larger sizes. More cutting
away of sound firm dentin and enamel is required than in any
other class of cavities. The proximating surfaces are broad, and
for success in preventing recurrence of decay, it is required that
these be cut away, so that the outlines of the cavity be free from
near contact with proximating teeth, and laid in such position
that they will be well cleaned by excursions of food over them in
mastication. Also, in making fillings it is of the utmost impor-
tance that the contact be restored in normal form for the protec-
tion of the interproximate gum septum, that this may be retained
in health and vigor. To do this effectually, it is required that
these fillings be finished to the full mesio-distal breadth of the
teeth.
Case.— A right upper first molar has a decay in its mesial
surface, which has been discovered by the patient because of a
slight breaking away of the mesial marginal ridge, disclosing the
cavity. Examination with the exploring instrument shows the
cavity to occupy about half of the mesial surface occluso-gingi-
vally and the middle two-fourths bucco-lingually in its extension
beneath the enamel, though the enamel opening is very much
smaller.
Procedure.— In these cases it always becomes a question
as to when the rubber dam and the Perry separator shall be
adjusted. It may be done first, or it may be done after the
cavity has been opened and the outline form roughly cut. But
it must always be done before the final shaping and trimming of
the walls and margins of the cavity is undertaken.
Opening the cavity.— With straight chisel 15, preferably
by mallet pressure, though hand pressure may be used, begin
chipping away the mesial marginal ridge of enamel overhanging
the decayed area, first toward the buccal, and then toward the
lingual, and continue until the enamel is found supported by
sound dentin. In the cutting, especially if done by hand pres-
sure, the edge of the chisel should be set very close to the mar-
gin to be chipped, and the enamel cleaved off in little flakes, the
direction of the pressure and the motion being almost in the line