Abstract
1. An investigation has been made to make clear the site of the excitation of the tooth tissues and the sensory and transmissive mechanisms of these tissues by thermal stimulations deduced from the action potentials evoked in the odontoblast cell area and the pulpal branch of the alveolar nerve.
2. The tooth responds to thermal stimuli when cooling or heating were applied on the amelodentinal junction and the pulp of the dog's canine. The least effect is found in the case of stimulation on the dentine. The temperature causing excitation, generally, ranges from 0°C to 20°C in the case of cooling and from 30° to 40°C in the case of heating. These values are essentially similar to those obtained in the skin and other organs sensible to thermal stimuli.
3. When cooling the amelodentinal junction, two contradictory biphasic action potentials are obtained from a micropipette electrode, large in diameter, inserted into the odontoblast cell areas, whereas a single biphasic action potential is obtained by a small micropipette electrode.
4. These action potentials evoked diminish by the use of narcotic agents, or destruction of pulp tissues.
5. Based on this available evidence, a discussion by the authors follows on the synaptic contact between the odontoblast cell and the nerve fibre in the tooth pulp and on the cause of the differences of the threshold values of temperature of thermal stimulations between the data of authors and the others.
