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74 PATHOLOGY OP THE HARD TISSUES OF THE TEETH.
CARIES OF ENAMEL.
ILLUSTRATIONS: FIGURES 75-98.
Caries of enamel, differs from caries of dentin in several
important particulars. (1.) In caries of enamel, the microorgan-
isms are attached to or lie upon the outside of the enamel. They
grow and form the acid which causes caries of enamel in that
position. They never enter the tissue until the enamel rods are
loosened and fall out. The enamel is a solid into which micro-
organisms can not penetrate. (2.) The enamel rods are cemented
together hy a cementing substance which dissolves more readily
in an acid than the rods themselves, and the first effect upon the
enamel is to dissolve out this cementing substance. The general
rule is that in decays occurring on the smooth surfaces of the
teeth, this cementing substance is dissolved through the entire
thickness of the enamel before any enamel rods fall away. In
some of the decays occurring in pits, the enamel rods themselves
will be dissolved, enlarging the pit. (3.) The decaying spot upon
the enamel is always whitened, as the first observable change.
This change in color is sometimes not considerable and is very
easily overlooked while the teeth are wet, but, when the teeth
are dried and examined carefully, the color will be found to be a
grayish white, or even very white in some cases, and the out-
lines are often very clearly marked. (4.) In such spots an
explorer is likely to catch if passed lightly over the surface,
instead of gliding smoothly as it will on sound enamel. (5.) For
these decays to occur, it seems to be necessary that microorgan-
isms become attached to the surface of the tooth, grow there in
the form of a colony, or in a zooglea formation, attached together
in a gelatinoid matrix, or equivalent covering, and produce fer-
mentative decomposition with acid formation at the spot, apply-
ing the acid directly to the solution of the tooth. (6.) For this
reason, the beginning of caries of the teeth occurs at such points
as will favor such lodgment or attachment in which the micro-
organisms will not be subject to such frequent dislodgment as
would prevent a fairly continuous growth. This is the cause of
the localization of the beginnings of caries on particular parts
of the surface of the tooth. It had previously been supposed
that caries of the enamel might be caused by acids dissolved in
the saliva, or introduced with foods from the outside. This
74 PATHOLOGY OP THE HARD TISSUES OF THE TEETH.
CARIES OF ENAMEL.
ILLUSTRATIONS: FIGURES 75-98.
Caries of enamel, differs from caries of dentin in several
important particulars. (1.) In caries of enamel, the microorgan-
isms are attached to or lie upon the outside of the enamel. They
grow and form the acid which causes caries of enamel in that
position. They never enter the tissue until the enamel rods are
loosened and fall out. The enamel is a solid into which micro-
organisms can not penetrate. (2.) The enamel rods are cemented
together hy a cementing substance which dissolves more readily
in an acid than the rods themselves, and the first effect upon the
enamel is to dissolve out this cementing substance. The general
rule is that in decays occurring on the smooth surfaces of the
teeth, this cementing substance is dissolved through the entire
thickness of the enamel before any enamel rods fall away. In
some of the decays occurring in pits, the enamel rods themselves
will be dissolved, enlarging the pit. (3.) The decaying spot upon
the enamel is always whitened, as the first observable change.
This change in color is sometimes not considerable and is very
easily overlooked while the teeth are wet, but, when the teeth
are dried and examined carefully, the color will be found to be a
grayish white, or even very white in some cases, and the out-
lines are often very clearly marked. (4.) In such spots an
explorer is likely to catch if passed lightly over the surface,
instead of gliding smoothly as it will on sound enamel. (5.) For
these decays to occur, it seems to be necessary that microorgan-
isms become attached to the surface of the tooth, grow there in
the form of a colony, or in a zooglea formation, attached together
in a gelatinoid matrix, or equivalent covering, and produce fer-
mentative decomposition with acid formation at the spot, apply-
ing the acid directly to the solution of the tooth. (6.) For this
reason, the beginning of caries of the teeth occurs at such points
as will favor such lodgment or attachment in which the micro-
organisms will not be subject to such frequent dislodgment as
would prevent a fairly continuous growth. This is the cause of
the localization of the beginnings of caries on particular parts
of the surface of the tooth. It had previously been supposed
that caries of the enamel might be caused by acids dissolved in
the saliva, or introduced with foods from the outside. This
