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the labial plate, it should be cut on the labial surface in the incisal third.
This preparation is the reverse of that shown in Fig. 25. In case both
labial and lingual plates are involved the preparation that is shown in
Fig. 30 with such modifications as are necessary to resist the labial stress
is indicated.
A method of preparing approximo-incisal cavities by cutting a series
of reverse curves, as illustrated in Fig. 32. may be used for the prepara-
tion of some cavities to prevent frail enamel walls. The advocates of
this method claim that this iregular outline results in a less conspicuous
line of demarcation betwx>en the porcelain and the enamel, and that the
series of reverse curves gives the essential acute angle resistance for the
porcelain of the inlay. It has been found advisable to drill a hole root-
ward (Fig. 32 A), which should be about No. 18 gauge. This hole should
run parallel with the axis of the tooth and should be from three to five
millimeters deep. It should be drilled after the matrix has been prop-
erly formed. Then a piece of threaded platinum wire. No. 19 gauge,
should be inserted into the hole and permitted to extend about two milli-
meters beyond the matrix. When the inlay is constructed, the post is at-
tached in the porcelain and ofiers additional retentive resistance after the
inlay has been set ( Fig. 32 B).

mcsto-DUto Incisal Cavities.
The question may arise with some as to the advisability of inserting
these large compound inlays instead of crowning the teeth. It must
always remain a matter of personal equation just when to substitute
crowns for fillings, but the author believes that a tooth with a vital pulp,
presenting sufficient structure to retain a filling for a reasonable period,
should be filled. Many times these fillings will last for years and v/hen
the filling is lost the tooth presents the same opportunities for crowning
that it did before it was filled.
The labial and lingual walls of both cavities should converge toward
the incisal edge and their margins should form right angles with the
curves of the surfaces (Figs. 33 and 34). Both labial and lingual plates
should be involved in the incisal third and the lingual plate should extend
farther gingivally than the labial (Fig. 34 and Fig. 35). The gingival
walls of both cavities should extend to the gum margin and should run at
right angles with their pulpal walls. If the pulp will permit, shallow tri-
angular cavities should be cut between the labial and lingual walls in the
gingival third, gradually diminishing in depth thr
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