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PREPARATION OP CAVITIES FOR PORCELAIN INLAYS 297
Finish of Enamel Walls. All finishing of enamel walls must be
completed before forming the matrix. The cavo-surface angle
should be a right angle as the strength of fused porcelain is about
equal to supported enamel margins. If a bevel angle exists it
should be deeply buried.
Toilet of the Cavity. This is attended to the same as with other
inlay fillings before forming the matrix.
Another Cavity Toilet
is necessary just before setting the in-
lay. This consists in washing the cavity with chloroform to dis-
solve any oily substances adhering to the cavity This
Avails. is

Fig. 159.—Cavity preparation for a Class Two porcelain inlay, non-vital case with the
porcelain occupying a portion of the pulp chamber.
followed with absolute alcohol and moderately dried. Excessive
desiccation is not required and in fact should not be practiced as
the integrity of the ceniental substance in the enamel is injured
and liability to marginal checking increased.
Preparation of Cavities of Class One. Defects in enamel. Porce-
lain is indicated in cavities on the labial surfaces of the six an-
terior, due to faulty enamel. These are shoAvn as small orifices
in the enamel surface, generally rounded in form, and is the result
of imperfect development. The cavity should be not less than two
millimeters in width at its narrowest point, as a smaller cavity
than this hinders proper working.