Electrical stimulation of tooth pulp in humans. I. Relationships among physical stimulus intensities, psychological magnitude estimates and cerebral evoked potentials.

Brief electrical pulses were applied to the pulp of individual pre-molar teeth of 14 healthy, adult volunteers via wire electrodes implanted and sealed in dentine. The sensation threshold was estimated in each individual by the Two-Alternative Forced-Choice Staircase (2AFCS) method. Seven, 5 or 4 stimulus intensities were employed which were equally spaced in a logarithmic scale between 10 microA above threshold and 500 microA. Magnitude estimates of the subjective intensity of the sensation produced by individual dental excitations were obtained. Cerebral tooth pulp-evoked potentials were simultaneously recorded in 11 subjects. The growth of psychological sensory magnitude with increasing strength of electrical stimulus conformed to the general psychophysical power law. Individual power function exponents varied from 0.204 to 0.907 with a mean of 0.475 and a standard deviation of 0.190. The amplitude of TPEPs, measured between components N135 and P293, also was a power function of stimulus intensity. The exponents of individual TPEP amplitude-intensity functions ranged from 0.055 to 0.362 with a mean of 0.144 and a standard deviation of 0.100. These last exponents were substantially smaller than those describing the growth of psychological magnitude estimates. Neither magnitude estimation nor TPEP amplitude-intensity functions displayed abrupt changes in slope which might accompany transition from one operating sensory mechanism to another and/or changes in qualities of subjective sensations from 'innocuous' to 'uncomfortable' to 'painful.' The result of our psychophysical and electrophysiologic experiments indicate that: (1) albeit highly specialized both morphologically and functionally, human tooth pulp has certain fundamental properties in common with other sensory systems and (2) late midline TPEP components may provide measures of central events that, within a range of stimulus intensities, are associated with the perception of pain, but should not be looked upon as specific indicators of pain processes.

Electrical stimulation of tooth pulp in humans. II. Qualities of sensations.

Individual premolar teeth of 22 normal volunteers were stimulated via intradentinal electrodes using brief electrical pulses. Questionnaires were used to determine the qualities of sensations produced by this stimulation. Operationally defined 'innocuous' sensations predominated between 1 and 10 dB SL, and were absent above 30 dB SL. Similarly defined 'painful' sensations were observed throughout the range of suprathreshold intensities but were most common above 20 dB SL. These findings demonstrate that non-painful sensations can arise from electrical tooth pulp excitation in circumstances in which spread of the stimulating current to periodontal and gingival structures is most unlikely. Two interpretations of these results are considered: (1) that tooth pulp afferents may have some unspecified sensory function besides mediation of painful sensations and (2) that they may be specialized in the mediation of nociceptive impulses but may give rise to innocuous sensations under special circumstances.