Page 167 - My FlipBook

pletc view of the whole case. Sections prepared in this way ;
must he stained hefore they are g-round. You may decalcify
the tooth, as I have indicated, with an acid—nitric acid three
per cent is very ^ood—and cut the sections witli the micro-
tome. In this plan you lose the enamel, but you retain all the
rest, but you will also lose the appearance of the hyaline zone
of Tomes, which is retained in the is^round specimen. Another
method w^ill be to select a case in which there is a thick layer
of softened dentin Take a spoon excavator and turn the whole
:
mass out ; this may be mounted on the microtone and sections
cut at once, or free-hand sections may be cut with a razor
these may be stained and mounted. This will often give an
excellent view of the micro-organisms in the decayed area, and
if it is carefully done the cut miay be made through the hyaline
zone of Tomes, and you will get the entire invasion of the
micro-organisms in this tissue. So far as views of micro-organ-
isms are concerned this latter method, which is very much the
simplest and quickest, answers the purpose perfectly, but it
does not give you its relation to the surrounding parts.
Ihc conditions under which caries begins in the enamel
and under which it may progress in the dentin are different.
They are different in this Upon the surface of the enamel in
:
beginning decay the micro-organisms are exposed to the vary-
ing conditions of the fluids of the mouth ; when implanted in
the dentin they are in a measure protected fro'm the varying
conditions in the mouth ; there seems to be no necessity that
they be protected by the formation of plaques ; they are pro-
tected from removal, and changes in the characters of the saliva
will not affect them so prominently. Therefore, it happens that
while very many decays begin upon the enamel and cease to
progress, most decays that have become implanted in the den-
tin continue until the tooth is destroyed, unless arrested by
artificial means. This is not always the case, however. The
conditions of the fluids of the mouth change as the person
grows older and become less favorable to the progress of caries,
and the beginning of caries in the enamel ceases almost entirely,
the person becomes immune ; but caries implanted in the dentin
will generally progress notwithstanding this— it will come
to progress very much more slowly, but still progress. Now,
in these cases, where the conditions have become unfavorable,
the decayed area, or the softened material, the amount of it,

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