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pared that it will not interfere with the withdrawal of the matrix. The
step should be as deep as the pulp will permit.
In all cases in which the enamel plates are thin
in the incisal third, or in which there has been an ex-
Step in
Cabial and Cingual tensive loss of the incisal angle, the step should
Surfaces. involve both labial and lingual plates of the incisal
edge (Fig. 28, A and B). This insures a stronger

Fig. 30. Fig. 31. Fig. 32.

mass of porcelain and greater protection to the enamel. It also prevents
the cement from changing the color of the tooth by reflecting through the
thin plate of enamel.
One of the weakest points of a porcelain inlay is the incisal margin,
if the enamel is beveled so that it is protected by porcelain, the thin margin
of porcelain which will be formed may be subjected to enough stress to
cause it to fracture. If the enamel is not beveled so that it is protected,
the enamel itself may fracture. In all cases in which it can be done, the
author tries to form the axial margin of the step near the center of the
tooth, thereby leaving the enamel rods running almost parallel with the
axis of the crown.
A step involving the labial plate should be so prepared that enough
tooth structure is involved to give a mass of porcelain sufficiently strong
to withstand the force of mastication, and to resist both vertical and

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