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CAVITY PBEPABATION. Ill

Fifth, remove any remaining carious dentin.
Sixth, finish the enamel wall.
Seventh, make the toilet of the cavity.
In certain conditions, which will be given in detail later, the
fifth of these should be placed as the second. These will be found
to be exceptions to the general rule.
The careful observance of this order of procedure by the
student will greatly facilitate his operations, lead to more careful
consideration of the requirements in individual cases and will
guide him to the use of the appropriate instruments for the dif-
ferent parts of the operation.
Outline form is the form of the area of the tooth surface to
be included within the outline or enamel margins of the finished
cavity ; the laying out of and cutting to these lines should be the
first thing considered and accomplished. In all pit cavities the
outline of the cavity will be found by cutting away all enamel
overhanging the decayed area, completely uncovering it, and fol-
lowing out any sharp grooves connecting with the cavity to such
points as will enable a perfect finish to be given to the margins
of the filling when placed. This should always be done before
there is any attempt made to remove the decay from the deeper
parts of the cavity. As these cavities occur in surfaces of the
teeth that are habitually cleaned by the abrasion of mastication,
except for lodgments in the pits or fissures in which the decay
begins, no further extension is required. In this class of cavities
this work is done generally with chisels and the enamel hatchets.
However, in the first opening of pits in which but little decay has
occurred, and in following out fissures and grooves, the bur is
often the best instrument.
In smooth-surface cavities, that is, in proximal cavities and
in buccal and labial gingival third cavities, which do not begin in
pits or fissures, but occur in the central portion of an area of
uncleanliness that is habitual, in which the superficial injury to
the enamel tends to spread, the laying out of the outline form of
cavities is done upon a different principle. In these it is not
simply cutting away overhanging enamel for the exposure of
the dentin already decayed, Imt the object should be to include
within the outline of the cavity such portions of the surface as
are especially liable to decay in the future. As decay is liable
to occur upon areas of surfaces habitually unclean, and only upon
the unclean areas, the whole of the habitually unclean area should
be included within the outline of the cavity. This requires a
careful study of the conditions surrounding each smooth-surface