Inflammation and dental pain in man

In the present article special interest has been focused on indicators of latent and manifest pulpal inflammation studied by psychophysical and electrophysiological techniques. Intradental A-delta nerve activity was recorded from two electrodes placed in the dentin on the labial tooth surface. The psychophysical measures were obtained by means of direct scaling methods in combination with sensory verbal descriptors. For stimulation cooling (ethyl chloride) and heating (hot guttapercha) of the tooth surface were employed. In addition, potentially algogenic substances, bradykinin and histamine, were administered on partly exposed pulps. Hot guttapercha induced a more complex neural response pattern than ethyl chloride. In all the recordings the responses evoked by heat showed a characteristic pattern consisting of three phases: an initial phase of short duration (i) followed by a depression in activity relative to the baseline (ii) and a slow spontaneously emerging activity in the absence of a physical stimulus (iii). The latter neutral event (iii) passed unnoticed by all the subjects. In the light of earlier experiments on feline pulp it was hypothesized that this third phase of the neural response was an indication of hyperexcitability in dental pulps and thus inflammation. Those subjects who experienced pulsating, dull, lingering pain (clinically diagnosed as pulpitis) showed a poor correlation between magnitude estimates of their mixed pain percepts and the total flux of A-delta nerve activity. Bradykinin and histamine evoked dull pain in the majority of cases probably caused by excitation of pulpal C fibers. In one experiment A-delta neural discharge of short duration could also be triggered by histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Encoding of the subjective intensity of sharp dental pain

This paper is a review and a discussion of our own pain research over the last decade. It is of a methodological and theoretical character and deals with preparation technique, choice of electrodes, control experiments involving pulpotomy and reliability tests of psychophysical methods for pain measurements, and the neuronal population encoding of sharp dental pain. The electrophysiological recording technique selectively picks up electrical activity induced in pulpal A-delta nerve fibers. The sensation of pain was quantified by means of an intermodal matching technique, finger span (PAS), in combination with sensory verbal descriptors covering a range from very, very weak to maximal pain. When a cold stimulus, ethyl chloride, was applied on the tooth surface a close agreement was demonstrated between intradental A-delta nerve activity (INA) and the sensation magnitude of pain (PAS) with respect to curve amplitude and time course. The high covariation of the neural and perceptual response measures indicated a good internal validity and confirmed also the basic soundness and the applicability of the procedures employed. For the purpose of further analyzing the functional relation of INA to PAS we studied specifically the effect of cold stimuli of different intensity on the integrated nerve response. Only sharp, shooting pain was accepted as a sensorial, perceptual correlate of the intradental A-delta nerve activity. Since an increase in amplitude was generally accompanied by an increase in duration of the responses, the fundamental question was raised how to best describe and characterize the neural and perceptual responses so that they most adequately reflect the information processing of the intensive aspect of sharp dental pain.(ABSTRACT TRUNCATED AT 250 WORDS)

The intensive aspect of information processing in the intradental A-delta system in man--a psychophysiological analysis of sharp dental pain

The tooth pulp has many attractive features for the study of peripheral pain mechanisms because of its rich innervation, its unique distribution of nerve fibers and its general disposition to give rise to pain upon stimulation. An experimental model has been developed for simultaneous recordings of intradental multi-unit A-delta nerve activity and the subjective intensity and quality of pain evoked by tooth pulp stimulation in conscious, alert humans. The only teeth to be considered for this kind of investigations are those having such a periodontal condition that they have to be extracted. The nerve activity was recorded from two electrodes placed in the dentin on the labial tooth surface, one at the level of the most incisal part of the pulp, and the other as far apically as possible. Brief cold stimulation was produced by using evaporating ethyl chloride administered between the recording electrodes. The magnitude of perceived pain was estimated by means of an intermodal matching technique (finger span) in combination with verbal descriptors. Of three response criteria selected--average response amplitude, peak amplitude and area under the response curve (integral)--for describing the relationship between intradental nerve activity and sharp, shooting pain, the integral yielded the highest mean correlation coefficient.

The relation between intradental nerve activity and pulpal pain after heat stimulation

The effects of tooth surface stimulation on intradental nerve activity (INA) and subsequent pain perception were studied in human lower incisors later to be extracted for periodontal reasons. The INA elicited by hot gutta-percha briefly applied to the tooth surface was monitored by means of labial electrodes deeply implanted in the dentin and perceived pain was continuously rated using a finger-span technique. After each stimulation the subject was also requested to select a sensory descriptor that was appropriate to describe the maximal pain intensity. The very first application of heat induced a typical pattern of nerve activity consisting of three phases. An initial burst of 3-5 s duration, phase I, was followed by a depression relative to the baseline lasting for 20-30 s, phase II, that gradually turned into phase III constituting a slowly increasing firing rate. The spontaneously emerging activity (phase III) in the absence of a physical stimulus passed unnoticed by all the subjects despite an average increase in firing rate of 67% relative to the prestimulus noise level. Repeated heat applications at short intervals led to a decrease and finally to abolishment of the whole nerve response. The lack of pain during phase III may be explained in two ways: the rate of increase in firing frequency may be too slow to trigger those perceptual pathways involved in processing of pain; the slow development of the increased sensory nerve activity may lead to central habituation.(ABSTRACT TRUNCATED AT 250 WORDS)