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208 OPERATIVE DENTISTRY
The Treatment of the First Class is the thorough disinfection
and then the application of phenol, full strength, for a few seconds,
Avhen the cavity should be dried and it will be found unaffected by
the blast of air from the chip blower. The change is brought about
by the superficial coagulation of the albumen in the exposed ends
of the dental tubuli which renders them non-conductive.
Second Class. If, after one or two applications of the phenol as
above, the distress from the blast of air is not relieved, or if the
pain is continuous while the surface of the cavity is exposed to the
air it is probably of the second class as met with in the nearer ap-
proaches to the pulp. This class of eases demands a media interven-
ing the dentine and the filling.
The Treatment in the Second Class is as follows: Moisten the
cavity with phenol and evaporate to comparative dryness. Then
paint the entire dentinal walls with a cavity varnish composed of
copal and gum dammar in alcohol and ether solution. Such a prep-
aration can be had at the dental depots or it can be prepared by the
druggist. This should be thin and spread evenly, applying one, two
or three coats and drying with a draft of air from the chip blower
after each coat. When the varnish is entirely hardened the filling
may be placed.
Third Class. In the deep-seated stage of caries, where large
quantities of dentine have been lost, even though the pulps may
seem to be protected by secondary dentine that is much retracted,
it is not safe to place a metal filling directly on the overlying den-
tine. The lost tooth structure should in a measure be replaced with
a material which is not a better conductor of thermal changes than
dentine. This should be neutral as far as irritating properties arc
concerned, non-changing and should resist the force necessary to
properly introduce the intended filling.
The Treatment in the Third Class is as follows: Phenolize and
dry. Varnish with the above cavity varnish and dry. Flow over
the dentine, covering most if not all of the axial or pulpal wall, or
both, according to the class of cavity being treated, a thin layer of
oxyphosphate of zinc cement, being careful not to include thereunder
any air bubbles; also apply without pressure. Then allow this to
set to complete hardness, when the filling may be completed. In the
three classes given above it will be noted that coagulation of the
protoplasm in the exposed ends of the tubuli was the first step. This
is good practice from the fact that this layer of coagulum is the
least irritant to the remaining protoplasm of anything of which we
have knowledge. Phenol is very limited in the extent of its action