Page 27 - My FlipBook

INTENTIONAL EXTENSION OF CAVITIES. 13

cavities are to be united. This will occur more in the
frequently
second than in the first molar, and more often still in the third molar.
I have advised extending the crown cavity into the palatal groove
of the superior molar, but in these cases the posterior fissure is usually
markedly continuous with the palatal groove. With the buccal groove
it is different. In the inferior jaw this groove often presents with its
widest toward the as it
part gum, narrowing approaches the crown.
If this groove is non-carious, it would usually be unwise to extend a
crown into
cavity it ; if slightly carious, it is generally good practice
to prepare the cavity pear-shaped, the apex toward the crown, and
not to actually connect the crown cavity with it. Where caries is
extensive at both must be united, but even then it is best
points, they
to unite them as little as possible, as by deep undercutting, the buccal
walls become much weakened. both cavities as
very Prepare though
they were to be filled separately, and then pass a bur along from one to
the other, making as shallow a channel as is compatible with strength.
Where a crown cavity in a bicuspid or a molar is but slightly sepa-
rated from an approximal cavity, the two should be united and filled
as one. If filled separately, the frail enamel partition must eventually
be crushed out under the force of mastication.
There is a kind of extension which is unfortunately too often neces-
A In
sary. patient presents to have the teeth cleansed. removing
stains along the gum-line of a molar, the enamel is found to have
become softened. Examination with a hatchet excavator demonstrates
that there are two, or perhaps three, small cavities in close juxtaposi-
tion. The rule here is The cavities must be opened up and
rigid.
formed into a single groove ; moreover, it must be extended as far as
the engine-bur will cut easily. All softened or softening material must
be cut away until firm margins are reached. I have known such pro-
cedure to involve the removal of nearly all of the buccal surface, and
once I so formed a cavity completely encircling the tooth near the
neck, but, as I have said, this is a rule which must invariably be
enforced. A somewhat similar condition, though from a different
cause and different in character, may arise from the use of a clasp-
plate. Here extension is indicated in another way. In the first
instance, we aim simply to reach a portion of tooth-substance which
is strong. In the second, this would not suffice. It will frequently
be found that the caries exactly marks the part of the tooth under-
lying the clasp, the cavity cleaned of decay showing just the form of
the clasp. Such a cavity should be extended in all directions, so
that when the plate is again placed in position the clasp will not touch
If this course is not
the tooth, but will rest against the filling. pur-
sued, it is plain that the width of the clasp and of the filling being the
same, the edge of one lies just along the border of the other. As all