RT Journal Article
SR Electronic
T1 RESPONSES IN DENTAL NERVES OF DOGS TO TOOTH STIMULATION AND THE EFFECTS OF SYSTEMICALLY ADMINISTERED PROCAINE, LIDOCAINE AND MORPHINE
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 89
OP 105
VO 130
IS 1
A1 Park Wayne Wagers
A1 Cedric M. Smith
YR 1960
UL http://jpet.aspetjournals.org/content/130/1/89.abstract
AB The nerves of the teeth of dogs were excited by mechanical, thermal and electrical stimuli, and the responses in single and multifiber nerve preparations of the inferior alveolar nerve described. Differentiation of responses evoked by thermal and electrical stimulation of the pulpal nerves from electrical activity in the periodontal mechano-sensitive innervation was accomplished. The pulpal nerves responding to thermal stimuli were not spontaneously active. Impulses were elicited by hot (> 55°C) or cold (< 5°C) water applied to the crown of the intact tooth. The maximum rate of impulse formation was determined principally by the temperature of the water and increased as the temperature was elevated. The range over which a stimulus temperature can be varied was limited by the threshold temperature (ca. 50° to 60°C) and by the danger of thermal damage with higher temperatures (ca. 75° to 80°C). Electrical stimuli were applied bipolarly through electrodes placed in drill holes in the tooth. The conduction velocities of the pulpal nerves were less than 40 m/sec with the majority between 15 and 30 m/sec. The response of the pulpal nerves to long duration (> 10 msec) constant voltage electrical stimuli of greater than rheobasic intensity consisted of a rapid repetitive formation of impulses. Increasing the stimulus voltage increased the number of impulses in the responses and also decreased the time interval (a) between the "make" artefact and each impulse and (b) between successive impulses of the repetition. It is concluded that these changes in artefact-impulse time interval were primarily the result of changes in the response time for the generation of the impulses. With the surface of the tooth kept dry, there was no significant spread of electrical current to periodontal tissue and the electrical stimuli were confined to the pulpal nerves. It is postulated that nonpainful or "tapping" sensations occurring in algesimetric testing and clinical dentistry when monopolar electrical stimulation of the tooth is employed arises from stimulation of nerves in the peridental tissue. The administration of lidocaine and procaine (2 to 20 mg/kg) resulted in a decrease in excitability of (a) pulpal nerves both to electrical and thermal stimulation of the tooth; and (b) mechanosensitive neurons of periodontal tissues. It is concluded that the effects of these local anesthetics were primarily the consequence of an elevation of threshold for excitation and not the result of inability of the nerves to generate or propagate impulses. The observed responses were a balance between two opposing factors: the dose of drug administered and the intensity of the stimulus. Morphine sulfate in doses of 2.5 to 5 mg/kg had no consistent effect upon these dental nerves and receptors. Interpretation of the effects of larger doses was confounded by concomitant changes in respiration or the presence of artificial respiration.