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Pathology of the Hard Tissues of the Teeth.

INTRODUCTION.

THE injuries which occur to the hard tissues of the teeth dur-
ing their development, and which occur to them by accident
or disease after they have grown, are peculiar to the enamel and
dentin. They have no apparent relation or natural kinship ^ith
similar developmental or acquired injuries or diseases of other
tissues of the body, except some atrophic injuries to the hair and
nails. This is made so by the histological structure of those
tissues, in that they have no power of repair and recovery from
injuries. The hair, nails, and the continuous growing teeth of
a few animals, while having no means of repair of developmental
or acquired injuries, dispose of the injured parts by the pro-
vision for the wearing away of the substance, and with this the
defects. Growth continues to supply new material, and in this
negative way may effect a repair.
The soft tissue appendages of the teeth, however, as the
pulps, peridental membranes, alveolar processes, gums, etc., are
developed under similar histological, physiological and patho-
logical laws as other soft tissues and bones; and possess similar
powers of repair.
The developmental injuries are confined to failure in develop-
ment of parts of the enamel and dentin because of general sys-
temic conditions which interfere with nutrition at a time when
some particular part of the tooth is being formed, or is growing,
and the injury is confined to that part. Other tissues have the
power of repair of such injuries later. Since the enamel and
dentin do not have this power of self-repair, such injuries in
them are permanent. There is a similar failure of self-repair
in these tissues when injured by accident or disease after they
have been formed, or have grown and completed their develop-
ment, such as accidental breakage of parts or injuries by erosion
or by caries. As these tissues are not subject to inflammation,
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