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ABSTRACT: Preferential blocks of peripheral nerves have shown that myelinated nerves are more susceptible to local compression and less resistant to asphyxia than unmyelinated fibers. Since two groups of functionally different nociceptors exist in the dental pulp, it is of theoretical and clinical interest to determine the influence of ischemia on the sensitivity of human dental pulp, using standard means for testing tooth vitality and at the same time investigating the intensity coding in one pathway of the afferent trigeminal system. Adrenaline was used to study the differential effect of adrenaline-induced ischemia on intradental A-delta nerve activity (INA) and the concomitant sharp pain, as well as on the detection threshold for monopolar electrical stimulation. Cold (ethyl chloride) and heat (heated gutta-percha) stimulation was applied to the tooth surface. In accordance with the hydrodynamic theory of dentin sensitivity the rapid fluid flow induced in the dentinal tubuli by these thermal stimuli is an adequate stimulus for selectively activating the A-delta nerves in healthy pulps. Consistency plots of the magnitude of the perceptual experience of sharp pain against the neural population response in linear coordinates yielded a high product-moment correlation, implying linearity for the intensity coding relationship. In contrast to the significant reduction of INA and its perceptual correlate of sharp pain after adrenaline administration, the electrical detection threshold remained constant during the full test period, suggesting that electrical threshold measurements have their limitations as a diagnostic tool or criterion for assessing the sensitivity of the dental pulp. The absence of A-delta activity was parallelled by no sensation of sharp pain. These findings suggested that the integrated neural A-delta activity constituted the underlying peripheral neurophysiological mechanism of the sensory intensity of sharp dental pain.
Endodontics & dental traumatology 03/1999; 15(1):6-16.
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ABSTRACT: This study examined negative volitional accommodation under open-loop viewing conditions by means of a coherent laser light pattern (633 nm) whose direction and velocity of motion is determined by the refractive state of the eye. Using the direct scaling procedure of free magnitude estimation, the subjects were required to quantitatively judge velocities of speckles when the retinal image of the subjects' eye was minimally influenced and when the subject was instructed to exert voluntary negative accommodation. Real-time, in-vivo measures of accommodation indicated that the dioptric strength of the crystalline eye lens was reduced under the condition of mental effort, and that the volitional accommodation values ranged between -0.26 and -1.90 D. The amplitude of these responses were noticeably correlated with individual measures of dark focus, so that larger dark focus values were associated with higher amplitudes of the voluntary negative response, and vice versa. By converting the dioptric strength of added optical lenses and the in-vivo measures of the eye lens curvature into angular velocities of laser speckles whose speed changes with focus relative the plane of stationarity, a specification of the proximal stimulus flow was obtained. The psychophysical functions describing the relationship between subjective speed and angular velocity generated either by placing lenses in front of the eye or by voluntary changes in accommodation had approximately the same appearance suggesting that the percepts reported by the subjects were valid and veridical estimates of the velocity of speckle movement.
Behavioural Brain Research 06/1994; 62(1):93-102. · 3.42 Impact Factor
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ABSTRACT: The speed of laser speckles induced by refractive defocus was determined by means of the direct method of free magnitude estimation in combination with sensory verbal descriptors. Physical measures of angular velocities were obtained by matching a similar pattern under the viewer's control to the laser speckles for equal subjective velocity. Theoretical speckle speed was calculated from geometrical formulae proposed by Charman [7]. The velocity percept of apparent speckle motion was a monotonic function of the refractive power of the positive lenses added to the observer's eye, although it exhibited a tendency of levelling off at the greatest strength. The magnitude estimates of this motion percept were highly correlated with corresponding subjective judgements of the angular velocity of the real motion of the matched pattern. Theoretical velocity plotted against empirically obtained values of velocity through matching yielded a product moment correlation coefficient of 0.98 and a regression coefficient of 0.94 indicating a high internal and external validity of these measurements as well as the usefulness of speckle speed as a cue for voluntary changes of the crystalline lens of the eye.
Behavioural Brain Research 06/1994; 62(1):81-91. · 3.42 Impact Factor
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ABSTRACT: The hydrodynamic theory of dentin sensitivity holds that pain is evoked by stimuli producing minute shifts in tubule fluid. In human volunteers hydrostatic pressures were applied to prepared dentinal cavities. The subjects reported the magnitude and quality of their sensations of pain by means of an intermodal matching technique in combination with verbal descriptors. No pain could be elicited when the smear layer was present. After removal of this layer, pressure stimuli of either direction evoked sharp pain. Rapid changes in pressure induced higher pain intensities than slow changes, indicating that the dental A-delta system is dynamic and gradient dependent. These results provide support for the hydrodynamic theory of dentin sensitivity and also lend credence to the notion that the movement of fluid across dentin induces a selective activation of the A-delta nerves in healthy pulps which is highly correlated with a sensation of sharp and/or shooting pain.
Journal of Endodontics 04/1994; 20(3):130-4. · 2.88 Impact Factor
