Page 43 - My FlipBook

gival wall of the step should form a right angle with the cancavity of the
lingual surface. A slight groove may extend along the approximo-labial
angle of the step in order to give additional retentive resistance. This
method of step preparation is considered unsafe for general usage. It
should never be used where great stress may be applied to the porcelain.
The weak point of the inlay is at the union of the porcelain for the cavity

Fig. 28 a. Fig. 28 B.

and the step, and an undue amount of stress will cause it to fracture at
this point.
In those cases in which the step extends from the incisal edge to the
gingival wall this wall should be flat. The labial margin should unite
with the gingival in the form of a curve and extend to the incisal edge in
the form of a straight line. It should form a right angle with the mesio-
distal curve of the labial surface. Enough of the labial wall should be
involved to insure sound enamel supported by dentine, and it should be
so prepared that it will form an obtuse angle with the pulpal wall. The
lingual wall should extend laterally about two millimeters further than the
labial and should run parallel with it. The pulpal wall should be convex
and form an acute angle with the pulpal wall of the step.

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