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Diseases of the Teeth. 75
The teeth of all persons are liable to be attacked by internal
caries, even of those, who have taken the utmost care to keep
them free of foreign matter from childhood.
The symptoms of internal and external caries, show that
The
their causes are different, as will hereafter be described.
first appearance of internal caries in teeth, that have been kept
free of foreign matter, is marked by a peculiar bluish or
dark spot, shining or appearing through the transparent ena-
mel, the integrity of which appears perfect; while the first ap-
pearance of external caries is on the outside of the teeth, the
enamel being first eroded ordissolved_by the chemical action of
foreign matter and the other agents to which they are exposed;
External caries, also occurs in different parts of the teeth, from
those of internal caries, and never attacks teeth that are kept
free of chemical agents and stand a little asunder.
The effects of climate, great and sudden changes of tempera-
ture, hereditary predisposition of the teeth to decay, or mal-
formation of their structure, inducing decay, most conclu-
sively prove, that the proximate cause of internal caries
is inflammation of the bony structure of the teeth, as it is cer-
tain that none of them could otherwise occasion caries. The
advocates for the doctrine, that caries always originates external-
ly, or on the surface of the teelh, must deny that the foregoing
have any effect upon the teeth, or their arguments fall to the
ground. We trust, that in the consideration of the particular
causes of caries* it will appear beyond a doubt, that all these
are prolific sources of caries of the teeth.
The denies sapientice are very liable to decay ; frequently
before they have completely pierced the gum, caries will ap-
pear in the centre of their crowns.
The teeth of young persons, are far more liable to decay,
than those of old persons ; and when attacked by caries, are
destroyed in far less time ; because, as we advance in life, the
vascularity of the teeth diminishes, and their structure becomes
more dense from the gradual absorption of the animal matter,
which enters so largely into their composition, and consequent-
ly they are less susceptible of inflammation; and also in the