The effects of various agents used to treat the hypersensitive teeth including KCl, KHCO3, K2C2O4 (K2-oxalate), KNO3 and CACl2 and those of agents used for pulp pro;tection or alleviation of dental pain including CaCl2 and zinc oxide eugenol on
intrapupal nerve activity (INA) were investigated in this study. We also observed the effects of natural stimuli such as sucrose and malic acid, and experimental pulpitis induced by compound 48/80 on INA. In cats anesthetized with sodium
pentobarbital,
the inferior alveolar nerve was dissected to expose single pulp nerve fiber units from ipsilateral canine under operating microscope. Units responding both to electrical stimulation and 4M NaCl were used to test the effect of various agents
applied
to
deep dentinal cavities for five minutes. INA elicited by each agent was calculated as the number of nerve impulses/minute for frequency analysis.
@ES The results obtained were as follows.
@EN 1. 17 single pulp nerve fiber units were classified as 14 Aδ-fibers and 3 C-fibers. Mean conduction velocity and electrical threshold of Aδ-fibers were 11.1±5.0klm/sec. 0.9±0.5V and those of C-fibers were 1.0±0.4m/sec, 1.7±0.6V,
respectively
2. 4M NaCl evoked an irregular burst of spikes which continued until the solution was washed completely. Only a few units responded to 0.5% malic acid and 3M sucrose, however 0.5% malic acid increased the INA el;icited by 4M NaCl in most units.
3. Application of compound 48/80 produced spontaneous INA with a latency of a few minutes, which remained unaffected unaffected with subsequent washing with physiologic saline, and increased the INA elicited by 4M NaCl in Aδ-fiber units.
4. In Aδ-fiber units, 1M KCl, 1M KHCO3, 1M KNO3 and 1M K2-oxalate remarkably reduced the INA elicited by 4M NaCl to 18.2%, 33.2%, 15.2% and 13.5%, respectively. Physiologic saline and 1M NaCl were not effective in reducing the INA, while 0.5M
and
1M
CaCl2 increased the INA.
5. In C-fiber units, isotonic CaCl2 failed to inhibit the INA elicited by 4M NaCl or 0.5% malic acid. Zine oxide eugenol decreased the electrical threshold and the conduction velocity slowly.
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