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CHAPTER V.

OUTLINE FORM.

Definition. Outline form is that part of cavity preparation which
determines the area of the tooth surface to be included within the
external enamel line.
Rule 1. Extend to Sound Enamel. All cavity margins should
be extended until all indications of surface decay have been in-
cluded.
Rule 2. Obtain Full Length Rods. If necessary, further extend
the outline until full-length enamel rods, supported by sound den-
tine, have been reached.
Rule 3. Self-Cleansing Margins. Extend the cavity outline un-
til the surface of the filling can be so formed that the enamel mar-
gin not protected by the gum will be mechanically cleansed by the
excursions of food in mastication.
Rule 4. In Relation to Developmental Grooves. A cavity out-
line should not follow a developmental groove, or parallel it so
closely as to leave a small strip of intervening enamel. The outline
should cross the grooves as squarely as possible.
Rule 5. Fissures and Sulcate Grooves. All fissures, sulcate
grooves and angular developmental grooves encountered should be
included Avithin the cavity outline. This comes in for the greatest
consideration Avhen part of the outline is laid on an occlusal sur-
face.
Rule 6. Enamel Eminences. The outline should avoid extreme
eminences of enamel and centers of primary development. Such
locations are subject to the extremes of stress during mastication.
When the eminence in question is the seat of primary calcification
it will be found to be less perfect in formation than the portion
midway from that point to the grooves.
Rule 7. Avoid Angles in Outline. The outline should be made
np of the greatest curves possible, avoiding all angles. Nearly flat
axial surfaces should show nearly straight lines or the segments
of very large circles, while on occlusal surfaces, which are made up
of a succession of depressions and eminences, the outline should
be a combination of smaller curves.
Rule 8. Outline in the Embrasures. The outlines in the labial,
buccal and lingual embrasures should be parallel to each other and
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