Journal of Dental Research, Vol 75, 553-561, Copyright © 1996 by International & American Associations for Dental Research Online Journals
Inflammatory lesions of the tooth pulp induce changes in brainstem neurons of the rat trigeminal subnucleus oralis
C. D. Torneck, C. L. Kwan and J. W. Hu
Department of Endodontics, Faculty of Dentistry, University of Toronto, ON, Canada.
Neuroplastic changes are known to occur in the CNS in response to injury of
peripheral nerves. Previous investigation has demonstrated neuroplasticity
in second-order neurons of the subnucleus oralis (SO) of the trigeminal (V)
nuclear complex in association with aseptic injury to the tooth pulp. A
question arises, therefore, as to whether similar changes occur in response
to injury associated with inflammation induced by tooth pulp infection. The
effects of tooth pulp infection on the mechanoreceptive fields (RFs) of SO
neurons were examined in rats. Infection was established by exposure and
removal of the coronal pulp of the mandibular first molar, which was left
open to the oral environment for 7 (n = 5) or 28 (n = 6) days. Neurons in
SO were then electrophysiologically characterized in
chloralose/urethane-anesthetized rats. The RF and the response properties
of 118 low-threshold mechanoreceptive (LTM) neurons from seven-day-old rats
and 149 LTM neurons from 28-day-old rats were compared with those of 204
LTM neurons tested in 11 untreated (control) rats. Significant differences
were noted in RF size and location when control, seven-day-old, and
28-day-old groups were compared. Radiographic examination revealed
inconsistencies among examiners in the interpretation of periapical lesions
< 2 mm in diameter and general agreement in the identification of
periapical lesions > 2 mm in diameter. Histological examination of teeth
with pulp exposure revealed superficial necrosis and inflammation without
periapical extension in the seven-day-old animals and total pulp necrosis
with periapical inflammation, abscess formation, and alveolar bone
resorption in the 28-day-old animals. The results indicate that
neuroplastic changes in LTM oralis neurons can develop subsequent to tooth
pulp infection and that there may be a correlation between the incidence of
these changes and the extension of the attending inflammation from the pulp
to the dental supporting tissues.
