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338 THE TECHNICAL PROCEDURES IN FILLING TEETH.

bicuspids and molars for gold inlays should be the same as for
porcelain, with the exception that the cavo-surface angle should
be beveled the same as for a gold filling. There should be good
depth in the step portion and also a dovetail to give the best
retention form.
Gold inlays are much oftener indicated than porcelain in
cavities of this class, principally on account of the fact that the
gold inlay permits of a strong and safe cavo-surface angle of the
enamel wall, and the inlay itself presents a margin which will not
be injured bj* the occlusion of the teeth of the opposite jaw.
Class 3. Cavities in the proximal surfaces of the incis-
ors AND cuspids, which DO NOT REQUIRE THE REMOVAL AND RESTORA-
TION OF THE INCISAL ANGLE. PoRCELAIN INLAYS. lu tMs CaSC the
prei^aration for placing the rubber dam will be the same as for
gold fillings. Generally the separation for gaining space between
the teeth will be the same, and about the same amount of room
will be required. But there will be many cases occurring where
the cavities are large and extend far to the gingival, in which the
claws of the separator will be in the way of the margins of the
matrix that must be fitted to the walls of the cavity and also
to all parts of the surface of the tooth about its borders. In
such cases, the Perry separator should be placed and a part of
the preparation of the cavity made at the first .sitting. The
space gained by the separator should lie as great as is consistent
with safety to the membranes of the teeth. Then the cavity
formed should be filled temporarily with gutta-percha, extend-
ing firmly against the proximating tooth in such form as to main-
tain, after the removal of the separator, the full separation that
has been gained. This should remain in place several days,
when, at the next sitting, the gutta-percha may be removed and
the teeth will remain apart, without the separator, long enough
to complete the operation. In a few cases it may be required
that this be done the second time to gain sufficient s)iace.
This separation may also be obtained by the older methods
of separation with rubber wedges or other means of slow wedg-
ing, but these cause so much more soreness of the teeth, and so
much more pain and trouble to the patient, that the more con-
venient Peri-y separator should generally lie employed.
The first thing to be considered in the preparation of prox-
imal cavities in the front teeth for porcelain inlays, is the fact
that the inlay must be inserted in one piece, and as the teeth
can not be separated sufficiently for the inlay to be inserted in
the direction of the orifice of the cavity as prepared for gold