物理的および化学的刺激に対する歯髄神経線維の応答性の変化

抄録

The purpose of the present study was to investigate the changes of response properties in the nerve fibers innervating the cat lower canine tooth pulp under a pathophysiological condition. In order to damage the pulp tissues, noxious heat and arsenic acid were used as stimuli of high intensity. The results obtained were as follows:
1. The nerve fibers were initially sensitized and subsequently desensitized. In the early stage, the electrical thresholds were lowered and some of the tooth pulp nerves showed spontaneous activities and also repetitive firings to a single electrical stimulus. In the later stage, their electrical thresholds were gradually elevated and some of them failed to respond to the electrical stimulation. Additionally, few of them further responded to dentin probing.
2. The changes of the responses in the fast conducting fibers, which were myelinated, were observed earlier than in the slowly conducting ones, many of which were unmyelinated, It was speculated that the initial changes occurred in the terminal endings of the myelinated fibers which are thought to be the receptive sites for the mechanical stimulation in the pulp.
3. These changes were almost the same in both types of stimuli.
These results suggest that the pulp nerve fibers are sensitized when intense stimuli are given to the dentin and that the myelinated fibers may mainly conduct pain information to the central nervous system in the early stage of pulpal injury. Subsequently, prolonged intense stimuli may alter the normal pulpal tissues into pathophysiological ones, resulting in the deterioration of the function of the myelinated fibers. Contrarily, unmyelinated fibers may maintain their functions and predominantly conduct pain information even in that condition.