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214 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
that, in the matter of extensions of cavities, simpler fillings, in
the technical sense, may be made, and have been made success-
fully in these cavities in the past. While this may be true of
some, too many have failed. Experience in cutting and filling
cavities, according to the rules given in technical procedures
in filling teeth, will, by comparison of results, show such sup-
posed simpler cavities to be lacking in prophylactic value. Decay
is continually recurring about the margins of the fillings when-
ever they are involved in habitual uncleanliness of even moderate
degree, and they are soon undermined and destroyed. For this,
extension for prevention, intelligently adapted to the conditions
and skillfully carried out, has been found an effective remedy.
LIMITATION OP EXTENSION FOR PREVENTION.
In the use of extension for prevention, there is no call for
extension around the angles of the teeth onto either buccal, labial
or lingual surfaces. Objection has been made in some journal
articles and society discussions, that cavities had to be cut inordi-
nately large in order to comply with the requirements, especially
in the front teeth. This is from a misunderstanding of what is
meant. In the front teeth, there should be no cutting over onto
the labial surface, nor should there be any considerable show
of gold fillings for the purpose of satisfying the rules of exten-
sion for prevention. Decay seldom begins on the angles of any
of the teeth, and especially is this rare in the angles of the
incisors and cuspids. When cavities in these teeth are so cut
that the margins approach the angles sufficiently to free them
well from near contact with the proximating teeth, extension
for prevention is satisfied. An approach to the angle on that
part of the surface rounding up to it is what is called for. Any
cutting beyond the angle is in direct opposition to extension for
prevention, because it is then approaching an area of surface
that is less safe. In the preparation of a cavity in an incisor
it should never be cut over onto the labial surface for the pur-
pose of extension for prevention. It is only when decay has
extended along the dento-enamel junction so as to undermine
and practically destroy a portion of the enamel of the labial
surface that it should be cut away. In these teeth, the necessities
for extension for prevention relate almost exclusively to broad-
ening the cavity to the labio-gingival and linguo-gingival angles
of the proximal surface, or squaring out the ordinary rounded
form of the gingival wall and making the labial and lingual
walls straight from near the incisal angle to the labio-gingival