This enables the tissue constituents of the
peripheral pulp to be alerted appropriately. Thus, in the
intact healthy tooth, a limited cold stimulus or elastic
deformation of dentin due to a sudden heavy load on
the tooth is transformed to minute and rapid movements
of the dentinal fluid (14). Such movements excite adjacent
nerves, resulting in a rapid reflex withdrawal reaction,
which is immediately followed by a brief, sharp
pain, alerting the individual to further withdrawal. This
is an important alarm system protecting the tooth from
overload leading to crown or root fractures by mastication
forces, for example (59).
In parallel there is a transient increase in blood perfusion
in the pulp (49). This is part of an instant local
defense reaction and is brought about by the fine terminal
branches of sensory nerves supplying both cells in
the odontoblast region and small feeding arterioles
deeper in the pulp. Excitation of the most terminal
branches in the peripheral area of the pulp results in a
reflex propagation of impulses in adjacent nerve terminals
belonging to the same nerves (axon reflex) (59).
Because these nerves contain vasodilating neuropeptides,
it takes only a few seconds for a short-lasting
(