Low frequency stimulation of peripheral nerves at adequate intensities often results in increased pain sensation and is mediated by central neural processes. Intraoral pain is mediated by trigeminal nerves; however, little is known regarding temporal summation of pain and intraoral stimulus parameters. This study assessed the effects of repeated stimulation of the gingiva on pain sensation in subjects using a device adapted for use in functional imaging environments. Measurement of psychophysical responses provide behavioral context for future investigations of intraoral pain processing using functional imaging methods.
Method:
A previously modified fMRI-compatible device was used to deliver punctate pressure-pain stimuli to gingiva apical of the maxillary right premolars. Data was collected from healthy female subjects (n = 24, mean age of 31 year). Mildly painful baseline pressure (1/10 intensity) was determined for each subject prior to temporal summation protocol. The summation protocol consisted of 6 runs of 10 mild pressure-pain stimuli with 3 different inter-stimulus intervals (ISI), which were 2, 5, and 10 seconds in duration, in a randomized block design. Data were analyzed by a two-way repeated measures analysis of variance.
Result:
For each ISI, reported pain ratings increased significantly from the first to tenth individual stimuli (p<0.0001). The increase in pain ratings at 2 second ISI was significantly higher than at 5 and 10 second ISIs (p<0.0001 for both). The reported pain increased during individual trials with greater pain intensity ratings occurring with runs that had shorter ISI duration suggests temporal summation occurred (Trial-by-ISI interaction p<0.0001).
Conclusion:
Pain ratings increased with stimulation of the gingiva in a frequency-dependent manner, in a similar fashion as observed by others. Experimental paradigm has acceptable properties to proceed with future experiments will rate pain sensation to intraoral stimulation while simultaneous high-resolution fMRI is used to assess brainstem activation.