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412 CONSERVATIVE TREATMENT OF THE PULP.
The composition of the dressing is based ujwn the considerations
that the nienstrunin is antisc])tic, and })ossesses some anesthetic value.
It also remains unchanged within the space and in time becomes, from
the dissipation of the menstruum, somewhat tirm in its character. The
therapeutic action of the menstruum when combined with the zinc oxid
is mild, and is employed for the reason that it is slowly given up by the
oxid, and therefore makes an acceptable dressing.
The Cap.—In all cases where metal fillings are selected it is essential
to use a metal cap. The methods where this is used are simpler and
better under control than when dressings are made without this appli-
ance. The reason for this is that the avoidance of compression is more
certain.
The caps are best when made of platinum, for the reasons that this
metal is a resistant material and the caps are easily formed.
AVhen the outer tilling is to be of gutta-percha or of the mineral
cements, caps may be formed of concave disks of pure tin. The tin
and platinum caps are stamped from the plate by the hollow punches
of the hardware shops, by Avhich means various sizes of round and
elliptical ones may be made. The effect of punching them upon the
end of a block of wood gives the suitable concavity to meet the require-
ments. For ordinary purposes they should be quite thin, but when
gold fillings are made over them the thickness and the concavity should
be such as to enable them to sustain the force applied. In cases where
there are indications of approaching congestion, or where it is probable
that the exposure is not recent, the dressing should have added to it a
portion of guaiacocain.
Placing the Cap in Position.—Placing the cap in position is a step
in the treatment requiring care. It should be assured that it is of suf-
ficient size to pass well beyond the borders of the ex-
Fig. 392.
posed organ, and in the approximal cavities it should.
cover the pulp wall of the cavity without intruding
upon the marginal walls. If there is a single exposure
it should be round ; if two cornua are exposed, either
two caps should be laid or one oval one employed, as
may best suit the case. In molars, usually, where two
points are exposed, two caps are generally best ; in the
bicuspid, one oval one under the same circumstances.
The cap should be inserted edgewise in such manner
that as it is laid in place the excess of dressing may flow
out at the margin toward the operator. This is to prevent undue
pressure, and to avoid air being included beneath the dressing, which
would prevent complete apposition of the dressing with the pulp.
In cases of easy access the cap may be laid in place with fine-pointed