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PORCELAIN AND GOLD INLAYS. 333

the esthetic point of view. It is for this reason, very largely,
that the porcelain inlay is not to be used in teeth from which
the pulps have been removed. If the inlay be adjusted ever so
nicely and the tooth becomes opaque later, tlie inlay will be off
color and become a blemish that will be worse than the sliowing of
a gold filling. When the pulp has been removed from a tooth
and the root canal filled under favorable conditions, I should not
hesitate to place a porcelain inlay, for I should not expect an
amount of discoloration that would be noticeable. If, however,
the tooth had come to me with a dead and decomposing pulp,
with abscess, or with the root canal open to the saliva, I should
expect discoloration that would prohibit the use of porcelain.
Prepaeation of Cavities for Inlays.
In the preparation of cavities for inlays, the general prin-
ciples of procedure are the same as described and illustrated in
this volume for other fillings in securing outline form, resistance
form, removal of decay, and in the use of instruments for all of
these purposes. The retention form is different. No convenience
form is necessary other than wall inclinations that are absolutely
necessary for the removal of the matrix or model. The finish
of the enamel wall is different for porcelain. In the main, the
cavities should be of the same outward form, except when cer-
tain extensions and enlargements must be made in case por-
celain inlays are to be used, in order to obtain a greater bulk of
porcelain for strength. The preparation for retention is dif-
ferent in that the inlays are cemented in place and the cavity
walls must be so cut that a perfect impression may l)e drawn
from them without in any wise marring its form. This is nec-
essary in order that the inlay may be correctly made and placed
in the cavity. Other changes are not necessary.
Many devotees of porcelain inlay work quickly forgot all
of their previous conservatism in cutting away valuable tooth
material and swung to greater width of cutting than the most
enthusiastic of those practicing extension for prevention had
ever done, and with much less regard for correct cavity outline.
This extravagance needs correction and toning down to reason-
able and correct lines that will have more regard for the struc-
ture of the enamel and the direction of its rods in the different
positions on the surfaces of the teeth. This is necessary in order
that there may be less chipping of the margins of both the enamel
and the inlay when porcelain is used. In the bicuspids and
molars, all proximal cavities involve the occlusal surface, and in
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