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lingual enamel wall should be in the form of a curve and should be
so prepared that it will give the strongest possible support to the in-
cisal wall. The pulpal wall should be formed in such manner that it
will not interfere with the withdrawal of the matrix. The incisal wall
should be a continuation of the lingual enamel wall. It should unite
with the labial wall so as to form an obtuse angle.
A step may be cut on the lingual surface in the gingival and
middle thirds (Fig. 15). This should extend laterally far enough to
give the required retentive resistance to the inlay. The lingual enamel
wall of the step should have a curved outline, and its pulpal wall should
form a right angle with the pulpal wall of the cavity.
In cavities involving both labial and lingual
surfaces, after frail walls of enamel have been re-
Cavities Tnvolvina
botb Cabial and moved and the margins have been extended to the
Cingual Surfaces. desired outline, all decay should be removed and
the cavity given such form as is required for the
retention of the filling.
The gingival wall should extend rootward sufficiently to carry the
margin of the inlay either to or beneath the gum margin. It should be
at a right angle to the pulpal wall and should have a shallow grove
running labio-lingually as far as it may be extended without interfering
with the withdrawal of the matrix (Fig. 16 A).
The labial wall should extend gingivo-incisally in the form of a
curve. It should be prepared so that its margin runs at a right angle to
the segment formed by the curve of the labial surface. (Figs, g C and
16 B). It would also form an obtuse angle with the pulpal wall.
The lingual wall should be cut freely to avoid any frail enamel.
It should extend from the gingival to the incisal wall in the form of a
curve. The plane of the curve should be parallel to that of the labial
wall (Fig. 18). Enough of this wall should be removed in the gingival
third to insure a strong mass of porcelain in this region.
The incisal wall should form an obtuse angle with the pulpal wall.
It should extend far enough from the incisal edge to provide a strong
wall of enamel.
The pulpal wall should be convex labio-lingually through the gin-
gival and middle thirds of the tooth (Fig. 16 C). It would join the
labial, lingual and gingival walls in the form of a curve instead of
sharp angles.
The cavity should be triangular in shape, with the base of the
tri-
angle toward the gingival wall, being formed between the labial and

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