Non-pain and pain sensations evoked by tooth pulp stimulation

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Abstract
This study investigated the quality and magnitude of sensations evoked by electrical tooth pulp stimulation. Detection threshold (the minimum current intensity that evoked a sensation) and pain threshold were determined for tooth pulp stimuli varying in frequency from 5-500 Hz. The effect of frequency and intensity of tooth pulp stimulation on the magnitude of sensations was assessed using visual analog scales and verbal descriptor scales. Detection thresholds were stable over experimental sessions and independent of the frequency of the stimulating current. Pain threshold varied as a function of frequency with a minimum value at 100 Hz. Stimuli that evoked nonpain sensations at low frequencies evoked pain sensations when frequency was increased from 5 to 100 Hz. Subjects were able to scale nonpain sensations over a range of stimulus intensities and frequencies. The lowest currents evoked sensations that were nonpainful and were of constant magnitude despite changes in the frequency of stimulation. Higher stimulus currents evoked sensations that were nonpainful at low stimulus frequencies and painful at high stimulus frequencies. Sensation magnitude at each stimulus intensity increased as a function of frequency. Temporal summation occurred in proportion to stimulus intensity. The nonpain sensations evoked in tooth pulp are mediated by a distinct population of afferents that are not involved in the coding of pain. High frequency stimulation that increased the discharge rate of the lowest threshold pulpal afferents resulted in no summation of nonpain sensation and never produced pain. High frequency stimulation evoked greater magnitude sensations at higher stimulus currents, indicating that central summation mechanisms were critical for higher threshold afferents signaling more intense nonpain and pain sensations.