Page 42 - My FlipBook

Jfpproximo Tncisal Gaoltics Ulith Steps.
The labial margin may extend from the gingival
^^'^" "-^ '^'^^ incisal edge in the form of a straight line
marginal
Outline. (Fig. 24 A), or it may extend from the gingival
margin to the incisal third in the form of a straight
line, then extend laterally in the form of a curve (Fig. 24 B and C).

Fig. 25. Fig. 26. Fig. 27.

Since the necessity for retentive resistance in-
creases in proportion to the increased width of the in-
Preparation
lay, a step should be made in large approximo-incisal
of the Cavities.
cavities to resist the tipping stress. The method of
cavity formation is, in a measure, dependent upon the method of step
formation. Steps may be formed by involving additional area of the
lingual surface. They may involve only the incisal third, they may extend
from the incisal edge to the gingival wall, or they may involve the middle
and gingival thirds. They may also be formed by involving both labial
and lingual plates in the incisal third.
A step may be formed involving only the lingual
plate in the incisal third of those teeth with thick
Step in
Cingual Surface incisal edges (Fig. 25). It should involve at least
Only. one-half the thickness of the incisal edge and extend
from three to four millimeters gingivally. The gin-

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