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302 OPERATIVE DENTISTRY

flat and meet both axial walls at an acute angle. The axio-labial
line angle should be acute. The lingual axial wall should be con-
cave. The axio-axial line angle should be a rounded angle and
continue out to the incisal cavo-surface angle.
Plan Four, Class Four. In angle restoration the creation of both
incisal and lingual steps is most popular. The incisal step is formed
in much the same way as when gold is to be used. However the
pulpal wall should be placed farther from the incisal edge and
be laid in a plan less acute to the axial wall than for gold.
The angle formed by the junction of these walls, the axio-pulpal
angle, should be rounded. In forming the lingual step the enamel
may be removed entirely to a level of the gingival wall, or it may
be only as much of the incisal portion as may seem necessary to
strengthen the body of porcelain in the incisal region and resist
the tipping strain.

Fig. 166.—A Class Four, plan three, for porcelain inlay.

The Double Step is of service in cases where there has been ex-
tensive loss of tooth structure, particularly in non-vital cases.
This plan results in a gingival wall and two pulpal walls; also in
two short axial walls placed on an equal number of levels. The
gingival and pulpal walls should be made to meet the axial walls
at acute angles. Each of the two pulpal walls should be grooved
from the connecting axial walls, and each axial wall in the central
portion resulting in a continuous groove from the gingivo-axial line
angle to the incisal edge. This cavity has draw directly to the
incisal.
Cavities Occurring in the Gingival Third of Class Five. Laliial
cavities in the gingival third are favorite places for porcelain and
should to a large measure displace gold. If the cavity extends be-
neath the gum line, the gum should be forced from position by