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30 THE TECHNICAL PROCEDURES IN FILLING TEETH.

Formulas of Side Instruments.
Hatchets, 5-3-28 and 3-2-28.
Discoid, 20, and cleoid, 20.
Of the three last groups of specials, the enamel hatchets
are rights and lefts, because of the form of the bevel of the cut-
ting edge. The spoons and gingival margin trimmers are
made rights and lefts by the curve of the blade. All the specials
are designed for special work. They are used, except the small-
est size of the spoons, almost exclusively in the bicuspids and
molars, and in these they should be used for almost all of the
work of excavating.
The chisels and enamel hatchets are used for chipping away
the enamel in opening cavities in the bicuspids and molars, and
in cutting the outlines to the required form. The enamel
hatchets are used especially for cutting away the buccal, lingual
and gingival walls of proximate cavities in these teeth and in
shaping them. Also, both the chisels and enamel hatchets are
used in the final shaping of the enamel wall and in beveling the
cavo-surface angle of the enamel.
The gingival margin trimmers are used for only the one
purpose of beveling the cavo-surface angle of the enamel along
the gingival wall of proximate cavities in the bicuspids and
molars. For this purpose one pair has the edge cut at an angle
of 80 centigrades with the shaft, which is right for beveling the
gingival cavo-surface angle of the enamel in mesial cavities, and
the other pair has the edge cut at an angle of 95 centigrades
with the shaft, which fits them for beveling the gingival cavo-
surface angle of the enamel in distal cavities.
The spoons are used for scooping out softened material
(carious dentin) from the deeper parts of carious cavities.
They should be used only after the walls have been cut to form
by other instruments. They are not at all suited to cutting
hard dentin.
Side Instruments.— There are four side instruments in the
set. They are called side instruments because their formulae do
not coincide with those of either of the other sets. Of these
the discoid (disc like) performs a service similar to the spoons,
i. e. , the removal of softened dentin from the deeper parts of
the cavity after the walls have been cut to form by other instru-