Introduction
A number of studies have demonstrated that voluntary exercise can modulate skin sensitivity in the limbs. Previously we have shown that also somatic sensitivity in the orofacial area can be modulated by masticatory-like activity. These movement-induced sensory changes are probably of importance for the optimization of sensory-motor integration. The aim of this study was to investigate the effects of stimulus duration, stimulus site, and rate of jaw movements on modulation of detection versus pain thresholds in human tooth pulp during cyclical jaw movements.
Methods
The effect of jaw movement on dental sensitivity to electrical stimulation was studied in healthy human subjects. Exercise consisted of continuous, masticatory-like jaw movements at two different frequencies (1 and 3 Hz). The detection (/perception) and pain thresholds of an upper or lower incisor were determined by monopolar constant current pulses using two different durations of the single stimulus pulse (0.5 and 5.0 ms).
Results
Without movement, the control pain threshold was significantly higher than the detection threshold, and both thresholds were significantly decreased with an increase of the stimulus pulse duration. Jaw movement produced a significant elevation of dental detection and pain thresholds, independent of the duration of the stimulus pulse. The jaw movement-induced elevation of detection thresholds was significantly dependent on the rate of cyclical jaw movements and on the site of stimulation. An elevation of dental sensory thresholds was observed only in the lower incisor but not in the upper incisor. Dental detection thresholds were significantly more elevated by jaw movement than dental pain thresholds.
Conclusions
The results indicate that cyclical jaw movements produce a segmentally restricted elevation of dental detection thresholds, whereas the modulation of painful dental stimuli is considerably weaker. The jaw movement-induced suppression of dental sensitivity may be explained by activation of afferent-induced segmental inhibition, corollary efferent barrage from motor to sensory areas, or both.
References