BACKGROUND: Knowledge of pain modulation from orofacial somatosensory stimuli with different valence (pleasant-unpleasant) is limited.

OBJECTIVES: To investigate: (1) The modulatory effects of painful, pleasant and unpleasant somatosensory stimuli on 2 models of experimental facial pain, (2) If modulation could be changed by blocking peripheral nerves via application of a local anesthetic: EMLA, or blocking endogenous opioid receptors via naltrexone, (3) If pain ratings were significantly correlated with participant psychological profiles.

METHODS: 38 healthy women received experimental facial skin burning pain or jaw myalgia for four randomised sessions on different days. The painful region was stimulated with mechanical or thermal painful, pleasant, unpleasant and control stimuli, with ratings recorded before and during stimulation. Sessions differed in pre-treatment: EMLA/naltrexone/placebo tablet/cream.

RESULTS: Significant effects of thermal or mechanical stimuli (P<0.017), but not session (P>0.102), were found on pain ratings for both models. In myalgia, painful cold resulted in a greater reduction in pain ratings than unpleasant cold, pleasant cold, control and pleasant warmth (P<0.004). Decreases in pain ratings from painful, unpleasant and pleasant mechanical stimuli was greater than control (P<0.002). In burning pain, painful cold resulted in a greater reduction in pain ratings than all but one of the other thermal stimuli (P<0.033). The pleasant mechanical stimulus reduced pain ratings more than all other mechanical stimuli (P≤0.003). There were no significant correlations between pain and psychometrics.

CONCLUSION: Valence targeted thermal and mechanical stimuli modulated experimental myalgia and skin burning pain (P<0.017). Partially blocking peripheral afferents or opioid receptors did not affect modulation.