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42 THE TECHNICAL PROCEDURES IN FILLING TEETH.
Of the groups of specials, the enamel hatchets are rights and
lefts, because of the form of the bevel of the cutting 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 smallest size of the
spoons, almost exclusively in the bicuspids and molars, and
should be used for almost all of the work of excavating in these
teeth.
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 and lingual walls
in occlusal or i^roximal cavities, and also in cutting and shaping
the gingival walls of proximal cavities in these teeth. 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 designed especially for
the purpose of beveling the cavo-surface angle of the enamel
along the gingival wall of proximal cavities in the bicuspids and
molars. These are the only instruments made that will do this
particular bit of work accurately and easily, and are essential to
accurate operating.
The spoons are used for scooping out softened material
(carious dentin) from the deeper parts of carious cavities in the
bicuspids and molars. Occasionally the smaller sizes are used
in the incisors. They should be used only after the cavity walls
have been cut to form by other instruments. They are not at all
suited to cutting hard dentin,
SIDE INSTRUMENTS.
In the University set we have but four side instruments.
The hatchets 5-3-28 and 3-2-28 stand to themselves as a range.
They are for the one purpose of cutting a retention groove in
the incisal angle of simple proximal cavities in the incisors and
cuspids.
Discoid 20-2-12 and cleoid 20, also single instruments, are
not connected with any set of ranges in the University set. The
discoid is found to be a very useful instrument. Sometimes in
cavities of easy access it will take the place of a spoon. It is used
much more, however, for catching and removing points of over-
lap of filling material about irrogularitios of the surface of the
enamel along the margins of cavities in the occlusal surfaces of
bicuspids and molars. It is, therefore, more of a finishing instru-
ment than an excavator.