Page 146 - My FlipBook

72 PATHOLOGY OP THE HABD TISSUES OF THE TEETH.
"Within my personal observation, caries of dentin has seemed
to progress most rapidly when closely shut in by overlapping
enamel, and less rapidly when the opening to the fluids of the
mouth was broad and ample. Finally, when the carious area
is so flat as to be kept clean by mastication and is fully exposed
to washings by the saliva, the decay ceases. The fungus is
facultative anaerobic, growing ordinarily in the presence of
oxygen, but having the faculty of growing quite as well in the
absence of oxygen. It grows well in culture media when all
oxygen is removed, and therefore grows as well when shut up in
a deep cavity. In case the opening of the cavity becomes very
broad while the cavity is yet shallow, the progress of decay
is apt to be much slower. The explanation for this difference
is that when the opening to the cavity is very broad, much of
the acid formed by the microorganisms is washed away by the
saliva. This must be considered a local factor. The intensity
of the condition of susceptibility, which will be discussed later,
must also be reckoned with as a general factor when considering
the rapidity of caries.
The progress of caries is limited, or even stopped, in a
number of different ways. The crowding of meats into a cavity
and the establishment of putrefactive decomposition, an occa-
sional occurrence, is apt to end the progress of decay for the
time, and leave the cavity with smooth, hard, blackened walls
by the decomposition of all of the organic matrix from which
the calcium salts have been removed. Decay may rebegin in
this if conditions are so changed as to favor it.
When most of the crown of a tooth breaks away, the prog-
ress of caries will necessarily be across the length of the dentinal
tubules, because these become horizontal on a level with the pulp
of the tooth. If the organisms are prevented from entering the
tubules from the pulp canals, the progress of decay will be very
slow, or there will be no progress at all.
WTien the pulp of the tooth has died and alveolar abscess
in the chronic form is established with a free discharge through
the root canals, the progress of decay is generally stopped as
long as this condition continues. If, however, the apical portion
of the root canal is choked by debris or otherwise closed, decay
may proceed from the root canal, penetrate the tubules and
rapidly hollow out the root to a conical shell and destroy it.
The breaking away of the lingual or buccal wall of proximal
cavities is often a factor in saving a tooth from destruction,
especially among those people who live much on coarse food.