It is commonly accepted that application of a sustained noxious stimulus frequently suppresses the perception of
pain. In this investigation, we have determined whether painful forearm
ischemia suppresses tooth
pain resulting from an acute irreversible
pulpitis. We have also determined whether the physiological responses to
toothache alter the perception of
pain evoked by experimental procedures. Ten male subjects experiencing a painful
toothache (group TA) and 7 age-matched
pain-free male subjects (group PF) participated in these studies. During session 1, heat pain threshold and tolerance values were determined for both groups. The times to ischemic
pain onset and ischemic
pain tolerance were determined for both groups using the submaximal effort
tourniquet procedure. The effect of the
tourniquet procedure on the intensity, unpleasantness, and spatial distribution of
toothache was also assessed. Session 2 was conducted on 7 TA and 7 PF subjects 1 week later and was conducted like session 1 with the exception that group TA was not experiencing tooth
pain during this session. Measures of thermal pain perception and forearm ischemic pain perception were not altered by the occurrence of
toothache. In contrast, sustained noxious forearm
ischemia produced a marked reduction in the intensity, unpleasantness and spatial distribution of pulpal
pain. These effects on pulpal
pain remained for at least 5 min after removal of the
tourniquet while the arm was
pain free. These findings suggest that a noxious conditioning stimulus does not universally inhibit pain perception but instead depends on unidentified interactions between the noxious test and conditioning stimuli.