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SENSITIVENESS AT THE TOOTH-NECK. 153

seen to anastomose with a nerve-fiber of the That
tively pulp itself.
it has the power of transmitting sensation is generally admitted. It
has also been universally observed that dentine immediately below the
enamel is more sensitive than elsewhere. Exactly at this point we
have what is termed the interzonal layer, as at i. The fibers of the
dentine bifurcate as they approach this territory and enter it, after
which can be traced as distinct fibers This
they only very sparsely.
might tend to the impression that this interzonal layer should be less
sensitive than the main mass of the dentine, but there is considerably
more matter here than in the denser where the tubuli
living portion,
are distinct. Dr. John I. Hart, in an able paper on this subject,*
claims that exactly at the neck ofthe tooth the character ofthe interzonal
layer changes, and that immediately underlying the cementum he
finds a granular layer. This I have not myself seen ; but the doctor
admits that this is very richly endowed with living matter, and so
accounts for the sensitiveness.
The mere exposure of this dentine, however, would probably not
cause any annoyance to the patient. This leads back to the state-
ment that after the recession of the gum the cementum begins to dis-
appear. I think this is probably due very largely to the tooth-brush,
the cementum wasting away by friction. This view is sustained by
the fact that though the recession of the gum may occur on the palatal
as well as the labial side, the sensitiveness will occur at the labial only.
At least I have never observed such a disturbance at the neck on the
side of of the anterior teeth, except when contact with a
palatal any
of an artificial denture had caused an abrasion or
part superficial
caries.
The destruction of the cementum, then, may be chiefly attributed
to the action of the brush, and, therefore, as soon as the dentine is
reached it will suffer from the same cause, so that presently the living
matter of the interzonal or granular layer becomes exposed. At
first it may be responsive only to contact, as when touched by the
bristles of the tooth-brush or by the finger-nail. Later it will give pain
when subjected to excessive heat or cold, or to the action of acids or
sweets.
the remedy is as simple as it is effec-
If taken in this early period,
tual. With a clean, smooth burnisher, rapidly revolved in the engine,
and
burnish the affected part, using considerable pressure, continuing
until the patient ceases to shrink. If this be thoroughly done, the
operator and patient will be astonished to observe that the part can
be touched How has it been accomplished ? Pos-
freely painlessly.
the sides of the
sibly it is that the burnisher drags together gaping
*See Dental Cosmos, p. 723, vol. xxxiii.