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Chapter TTT.
Preparation of Cavities.
Approximo-Incisal Cavities; Formation Without Step; Formation With Step. Mesio-
disto-incisal Cavities, Cavities Involving Incisal Edge. Teeth Affected by
Malformation and Erosion. Cavities in Bicuspids and Molars.
Jlpproximo-Tncisal Cavities.
Approximo-incisal cavities may be divided into two classes
Approximo-incisal cavities involving but a small portion of the incisal
angle and where no step is required for retentive resistance ; and
approximo-incisal cavities involving enough of the incisal angle to re-
quire a step for additional retentive resistance.
Preparation of Cavities Ulithout a Step.
The gingival margins should be slightly concave in a labio-lingual
direction (Fig. 20 A). This gives the shortest possible bevel to the porce-
lain in the linguo-gingival region, thereby insurmg less liability to frac-
ture. The labial margin should be cut laterally far enough in the gingival
it should unite with the gin-
region to avoid a frail margin of porcelain ;
gival margin in the form of a curve and extend incisally in the form of
a straight line (Fig. 21 A). The labial margin should run at right angles
to the curve of the segment of the circle formed on the surface (Figs. 9 C
and 17 B). The lingual margin should extend from the gingival wall to
the incisal edge in a straight line, and it should be cut as far laterally as
the labial margin. This margin by being sufficiently extended in a gin-
gival direction, should involve enough of the gingival ridge to provide
for a thick mass of porcelain in this location (Fig. 21 B).
The gingival wall should be slightly grooved
^^^ should form a right angle with the pulpal wall
Tortniltion
it should extend far enough rootward to protect the
el the CapitV.
gingival margin. A shallow groove should be cut
from the labial to the lingual wall, but care is to be taken that this groove
34
Chapter TTT.
Preparation of Cavities.
Approximo-Incisal Cavities; Formation Without Step; Formation With Step. Mesio-
disto-incisal Cavities, Cavities Involving Incisal Edge. Teeth Affected by
Malformation and Erosion. Cavities in Bicuspids and Molars.
Jlpproximo-Tncisal Cavities.
Approximo-incisal cavities may be divided into two classes
Approximo-incisal cavities involving but a small portion of the incisal
angle and where no step is required for retentive resistance ; and
approximo-incisal cavities involving enough of the incisal angle to re-
quire a step for additional retentive resistance.
Preparation of Cavities Ulithout a Step.
The gingival margins should be slightly concave in a labio-lingual
direction (Fig. 20 A). This gives the shortest possible bevel to the porce-
lain in the linguo-gingival region, thereby insurmg less liability to frac-
ture. The labial margin should be cut laterally far enough in the gingival
it should unite with the gin-
region to avoid a frail margin of porcelain ;
gival margin in the form of a curve and extend incisally in the form of
a straight line (Fig. 21 A). The labial margin should run at right angles
to the curve of the segment of the circle formed on the surface (Figs. 9 C
and 17 B). The lingual margin should extend from the gingival wall to
the incisal edge in a straight line, and it should be cut as far laterally as
the labial margin. This margin by being sufficiently extended in a gin-
gival direction, should involve enough of the gingival ridge to provide
for a thick mass of porcelain in this location (Fig. 21 B).
The gingival wall should be slightly grooved
^^^ should form a right angle with the pulpal wall
Tortniltion
it should extend far enough rootward to protect the
el the CapitV.
gingival margin. A shallow groove should be cut
from the labial to the lingual wall, but care is to be taken that this groove
34
