Page 221 - My FlipBook

EEMOVIXG THE DECAY. 219
caries,—a product resulting- from this disintegrating action upon both
the organic and inorganic constituents of dentin. In nearly all cavi-
ties we iind tu-o raricties of alfercd tissue. That nearest the surface is
a mass of thoroughly disorganized and usually decomposed matter filled
with micro-organisms. Beneath this and lying next to the healthy den-
tin there is a zone or layer from which the calcium salts have been re-
moved by the acid solvent, but which still retains its original form and
vitalitv. This layer of decalcified dentin may be allowed to remain,
especially in the bottom of a cavity, as it serves to protect the subjacent
tissue from thermal shock and will in the great majority of cases be
again converted into normal dentin by the re-deposition of calcium salts.
As a precautionary measure, however, it should be treated to an applica-
tion of some germicide such as carbolic acid, mercury bichlorid, for-
malin (10 per cent, aqueous solution), or oil of cinnamon, before the
insertion of the filling.
Occasionally caries will be found to be sclf-Umitcd. In such
cases, through some unexplained change of conditions, the progress
of caries has been checked and the layer of decalcified dentin re-
stored to its previous normal condition. AYhere this has taken place
the restored tissue is usually of a darker color than ordinary dentin,
and on this account may be mistaken for carious dentin and removed.
It is, however, easily distinguished from caries by its hardness, and
should in no case be removed except from the sides of a cavity, and
then only when its dark color showing through the walls would prevent
the cavity, after being filled, from having that clear and clean appear-
ance which it should possess.
With some practitioners it is the custom to prepare a cavity dry,
because in this way the operation is more rapid and usually less painful.
In such case the rubber dam is ajiplied first of all and the operations of
0})ening, cleansing, and shajiing the cavity are all performed without
the presence of moisture. Repeated applications of warm air from a
syringe, at intervals during the operation, desiccate the dentin and di-
minish its power of sensation. Others, in order to avoid the unpleasant-
ness to the patient of having the dam in position for so long a time,
prepare the cavity roughly in the presence of moisture, then apply the
dam, dry the tooth thoroughly, and finish the operation.
Whichever plan is adopted it is absolutely necessary, in all cases, to
finish the preparation with the dam on and the tooth dry, for it is only
after a tooth has been deprived of its moisture that we are able to
decide whether all the niceties of preparation have been successfully
carried out. Certain marginal and structural defects that are not
noticeable while the tooth is moist are plainly revealed after it has been
(h'icd.