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CHAPTER XXXIII.
TREATMENT OF HYPERSENSITIVE DENTINE.

Hypersensitive Dentine is dentine which is more than normally
responsive to mechanical or chemical irritation.
Normal Healthy Dentine is only slightly sensitive, but Avhen ex-
posed to abnormal conditions and irritating agents it may become
excruciatingly hypersensitive.
The Sensations Are Conveyed to the Pulp by means of the con-
tents of the dental tubules which are prolongations of the odonto-
blasts. The odontoblasts are thickly surrounded by the terminal
fibers of the nerves within the pulp.
The Contents of the Tubuli is largely protoplasm and although
this has the power of transmitting sensation in response to irrita-
tion, it has not yet been demonstrated that the nerve fibers enter
the tubuli or penetrate their contents. Hence it cannot be said
that there is nerve tissue Avithin the dentine.
The Direct Cause of Sensitive Dentine is the loss of the enamel
which is the natural covering of the dentine.
The Most Common Agent in the removal of this normal covering
is caries, which exposes the dentine to mechanical injury through
contact with foreign substances and chemical irritants, particularly
the acids of fermentation.
Rapidity of Caries has much to do with the degree of hyper-
sensitiveness in dentine, as shown in the white and light stages
or rapid forms of caries wherein the sensitiveness is most exalted,
while with the dark, yellow and brown varieties it is not so marked
and with the black or slow progressing form of caries the sensitive-
ness is scarcely above normal.
The Most Sensitive Part of a Carious Tooth is at the junction of
the dentine with the enamel or cementum at the periphery of the
tubuli. It is therefore evident that the second stage of caries will
show a higher degree of hypersensitive dentine than the deep-seated
stages and that the preliminary steps in cavity preparation in this
division of caries will be more painful than the deeper cuts into the
dentine, as then the more sensitive part has been passed.
Mechanical Abrasion is also an agent Avhich produces hyper-
sensitive dentine by first wearing away the enamel and then en-
croaching on the dentine. However, this process may be so slow
and the irritation so slight as to act as a stimulus to the odontoblasts
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