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PREPARATION OF CAVITIES FOR, PORCELAIN INLAYS 299

Cavities in Proximal of Incisors and Cuspids Not Involving the
Angle. Class Three. This class of cavity is ideal for porcelain in-
lays and is by far the most sightly filling Avhen properly done.
These Cavities Should be Divided Into Two Classes in accord-
ance with the three different lines of approach.
First division, labial approach; second division, lingual ap-
proach.

Fig. 162.—A Class Three cavity lingual approach for porcelain inlay.

Labial Approach. This approach should be decided upon when
any considerable amount of the labial enamel is to be replaced and

a lingual wall is possible. (Figs. 160 and 161.)
The Gingival Wall should be extended gingivally to include ail
affected enamel. It should be flat axio-proximally and meet the
axial wall at an angle slightly acute. It should meet the lingual
wall at an angle slightly obtuse.
The Axial Wall should be flat labio-lingually and be continu-
ous from the axio-lingual line angle to the labial cavo-surface angle
which results in the entire removal of the labial wall. This wall
should meet the lingual and incisal walls at an acute angle. The
incisal lingual line angle should be slightly obtuse. This results