Gender difference in masseteric exteroceptive suppression period and pain perception

Objective Use of brain stem reflexes in the assessment of orofacial function requires insight into the influence of demographic factors such as gender. The aim of this study was to characterize possible gender differences in the relation between quantitative measures of the masseteric exteroceptive suppression (ES) reflex response and pain perception evoked by incrementally increasing electrical stimulation. Methods In 12 men and 12 women, the surface electromyogram was recorded from the left masseter muscle. Thirteen fixed stimulus intensities from 5 to 35 mA at 2.5 mA increments were applied to the skin above the left mental nerve. The stimulation intensity at which the late ES appeared first and the first intensity at which the subjects reported the stimulus intensity to be painful were defined as the reflex threshold (RT) and pain threshold (PT), respectively. Furthermore, data were analyzed using stimulus–response curves, and the reflex appearance levels (RAL), the saturation level, the slope from appearance to saturation of the reflex (SLP), and the pain appearance level (PAL) were determined. Results The PT was equal to or higher than the RT in 9 of the 12 men, but only in 4 of the 12 women. Further, women had significantly lower PAL, RAL, and SLP (12.7±0.8, 12.9±1.4, and 3.0±0.9 mA, respectively) compared to men (20.3±1.6 mA, 16.7±1.1 T, and 4.1±0.4, respectively) (P<0.05). Conclusions The present results document that women have a lower reflex threshold and pain threshold to cutaneous electrical stimulation than men. Significance These findings suggest that gender differences may exist in the sensory–motor integration of primary afferent input from the orofacial region and that these differences should be considered in the design of future reflex studies.