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744 DENTAL CARIES. —
has been most thoroughly studied, seemingly in all possible aspects,
but -without results. At the present time the only influence that we
can attribute to vitality is that it has some power to limit the rapidity
of decay in the otherwise normal tooth. Teeth that have lost their
pulps, and as a result the vitality of the dentine, decay more rapidly.
The great number of pulpless teeth now retained in the mouth
give abundant opportunity for observation upon this point ; but it is
uncertain whether this slower progress of caries in the living tooth is
on account of its vitality or because the tubules are occupied with the
dentinal fibrils in such a way as to prevent by their bulk that more rapid
ingress of the agent of solution which would occur were the tubules
laid open by the loss of the fibrils. This latter thought seems to be
more in harmony with the phenomena, and yet it must be admitted that
it is difficult to conceive that the living contents of the tubules, the den-
tinal fibrils, should be powerless and incapable of exerting any influence
when their vitality is directly disturbed. Yet, after all the study that
has been expended on this point, there have been developed no evidences
of vital resistance on the part of the dentine itself, other than hyperses-
thesia, capable of withstanding adverse criticism.
The principal evidence of vitality of the dentine, however, is exhib-
ited in changes that occur in the tissues of the pulp itself on account of
irritation of the distal ends of the dentinal fibrils in the processes of
caries and of the abrasions. These are fully considered in the article
on Pathology of the Dental Pulp, and need not be referred to here,
especially as they do not relate to caries further than that they are one
of its remote consequences. The fact that these morbid effects are trans-
ferred to the pulp through a considerable portion of dentine, without
visible change in the dentine itself, denotes its incapacity for the exhibi-
tion of morbific changes through vital activity or the agency of vital
forces resident within itself.
A few observers seem to have abandoned both tli»e chemical and the
vital theory, and have sought to explain the results by other means.
Bridgcman, in an essay on this subject,* attributes caries to peculiar
electrical conditions in which the crown of the tooth becomes the pos-
itive electrode, and the tissues in which the tooth is invested the nega-
tive. When these conditions are intensified by abnormal qualities of
the fluids of the mouth, the crown porticm of the tooth yields up its
lime salts, setting free the acids with which they were combined ; and
this leads to molecular disintegration of the substance of the dentine in
the form of caries. This is certainly a very ingenious theory, but is at
variance with so many facts that any eff(>rt to maintain it must be futile.
It can be readily understood, however, that by placing different metals
in the teeth as fillings the saliva may act as an excitant and a battery
be produced. From these artificial conditions I have seen effects that
seemed to be the product of electrical currents.
Another thought has been advanced to account for caries on the
hypothesis of vital action. In this it is supposed that on account of a
disturbance of vitality, such as might produce inflammation in other
parts of the system, the imtrition—or, more properly, the vital action
* TninsactwiiH Odontulogicul Soc, vol. iii. p. 369.