Page 192 - My FlipBook

190 PRELIMINARY PREPARATION OF CAVITIES, ETC.

the altered relation of tlie mucosiim. The analogy is further borne out
by the fact that in each instance a })rotcctive covcrino- affords salu-
tary relief.
The normal scnsitiyity of dentin is not high, as is shown by an
immediate examination of a surface exposed l)y accident, but after a
fe^v days the; denuded surface manifests impatience of mechanical
contact and of applications of cold, which pi'oyes that the altered rela-
tions induce a condition of the part similar to the condition of the
skin when the epidermis is broken. This appears to be the case in-
dependent of the influence of chemical agencies, as exaltation of sensi-
tiveness occurs when the fluids of the mouth are in a normal state.
The same indications are presented when a non-sensitive cavity is pre-
pared, as here, in case the cavity be not protected by a stopping, the
same phenomenon subsequently appears.
Generally also, in such cases, if a stopping is inserted without pre-
viously effecting a coagulation of the surfac(> of the cavity, pain arises
upon reduction of temperature. This condition is designated as sec-
ondary sensitivity, which is caused by the traumatism. In some cases
of this kind the pain becomes so great as to require the removal of the
stopping and the carbolization of the cavity. In extreme cases reflected
pain in the other teeth may appear in consequence of the disturbed
relations making an impression upon the nervous elements of the pulp.
When exposure of the dentin has been brought about by ccaies, the
sensitivity excited is liable to be much exalted above the normal, and is
only prevented from giving constant indications of this condition by
the presence of the carious matter, which, being a poor conductor of
heat, in a measure protects the pulp from thermal irritation. This
accounts for the fact that while there may sometimes be acute pain in
the early stages of decay of dentin, the irritability and reaction of the
pulp appear to become less as the caries adyances.
When the teeth are undergoing rapid decay the dentin is more sen-
sitive than when the carious process is slow. As the color of the
carious matter gives some indication of the rate of progress, we may
from this indication form an impression of the probable degree of
sensitiveness. When the carious matter is light, the action has been
rapid ; when it is yellow or light brown it is less active ; and when it
is dark brown or black, it has progressed very slowly. In some cases
of the last character, when the parts are subject to friction, spontaneous
cessation of decay takes place. The parts are then nearly devoid of
sensitiveness. The process by which the dentinal tubuli become oblit-
erated by calcific deposits is called ebuDiation. AVhcn the dentin be-
comes exposed by attrition, that tissue is not as greatly irritated as it is
by the progress of caries, since by reason of the gradual loss of sub-