Relation between electrical stimulus intensity, masseteric exteroceptive reflex and sensory perception.

PURPOSE

The purpose of this study was to characterize the relation between stimulus intensity, masseteric exteroceptive suppression (ES), and sensory perception as a possible quantitative or qualitative tool in the diagnosis of the masticatory system for prosthodontic treatment.

METHODS

From 12 males and 12 females (22-41 years), surface EMG was recorded from the left masseter muscle. Visual feedback allowed the subjects to maintain a constant clenching level of 30% maximal voluntary contraction. Thirteen fixed stimulus intensities from 5 to 35 mA in 2.5 mA increments were applied at random. A computer program calculated the duration of ES, based on the 50% level of the mean pre-stimulus EMG. The stimulation intensity at which early (ES1) or late (ES2) exteroceptive suppressions appeared first and at which subjects answered as being painful were defined as the reflex threshold (RT1 or RT2) and pain threshold (PT), respectively. The relation between sensory perception and ES was evaluated using stimulus-response (S-R) curve analysis.

RESULTS

Significant differences were found between PT and RT1, and between RT1 and RT2 (P<0.001). After S-R curve analysis, the maximum duration of ES1 and ES2 was estimated at 9.6 ms and 33.5 ms, and appearance was rated as 6.2 and 4.0 on numeric rating scale (NRS), saturation was 7.6 and 6.9, and slope was 7.0 and 11.2, respectively.

CONCLUSIONS

All parameters for changes in ES following increasing incremental stimulus intensity could be analyzed. The construction of S-R curves in relation to sensory perception and ES parameters characterized the difference between ES1 and ES2.