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212 PRELIMINARY PREPARATION OF CAVITIES, ETC.
tubules, it is not difficult to limit the action to this part by the means
al)()vc pointed out if care be taken in the required procedures.
The Acids.—Chromic and nitric acids arc of service in extremely-
shallow cavities of very high sensitivity. The former acts by coagula-
tion of the organic elements of the dentin and the latter by decom])osi-
tion and solution. To apply these the adjacent tissues require to be
protected. Each should be carried in small quantity upon a gold
])robe.
Nitrate of silver is applicable for reducing the sensitivity of dentin
after the removal of superficial caries or when by abrasion or by erosion
the exposed tissue is intolerably sensitive. It is, however, only to be
used in the back of the mouth on account of the discoloration which it
produces.
Chlorid of antimony is applicable only to cases of exposed cemen-
tum, where it is claimed that it is equally as efficient as silver nitrate^
and has not the objection of discoloring the tissue.
General Anesthesia.
While some reluctance should exist as to the propriety of inducing
general anesthesia, it sometimes becomes necessary to resort to this
means of alleviation. Necessity for this election arises where the sen-
sitivity is extreme, when the previous remedies have been inefficient,
and when from the nature of the case zinc chlorid is inadmissible^
The subjects should generally be adult persons of intelligence, who
possess moral force and, having confidence in their adviser, are capable
of giving the requisite indications of the progress of the anesthetic
influences.
Sulfuric ether is the most suitable anesthetic to be employed, and
the operative procedures should be performed in the first stage, that
of peripheral anesthesia. At this period, which is before the stage
of excitement commences, dentin may be cut without the slightest
pain being felt. This is an important consideration, since if the ad-
ministration is continued into the period of excitement nothing can be
done, and if it is conducted to a full degree the patient is not manage-
able. Also the subsequent depression is to be avoided. While general
anesthesia in the first stages is available for the relief of dentinal sensi-
tivity, it is found, on the contrary, when resorted to for the removal of
the pulp, as may occasionally be required in the most severe cases of
congestion, that nothing short of profound anesthesia will suffice.
When the first stage is reached, the patient being conscious and able
to reply to questions, the cutting is commenced ; as the pain returns a
few more inhalations are given, when another part of the cutting may
be proceeded with. This may be repeated until the cavity is formed.