A Quantitative Study of Thermal Detection and Thermal Pain Thresholds in the Trigeminal Region

Objectives: Quantitative thermal sensory testing can be used to evaluate the function of small diameter nerve fibres in patients with nerve injuries or other neurological abnormalities. The ability to detect a change in temperature or the threshold of thermal pain sensation is recorded, but there is limited information concerning these values in the trigeminal region. We have quantified thermal sensitivity on the tongue and in the mental region of healthy adults, and have assessed the reproducibility of these results after different intervals. Methods: Forty healthy adults (24 female and 16 male, age range 21-54) were divided into two groups and either the dorsal surface of the tongue or mental region was tested. The warm detection threshold (WDT), cold detection threshold (CDT), warm pain threshold (WPT) and cold pain threshold (CPT) were measured bilaterally and the measurements were repeated after 30 minutes and approximately 1 month. The tests were undertaken using a 256mm² peltier thermode (Medoc Thermosensory Analyser, TSA II, Israel) in a quiet room, with a baseline temperature of 32^oC. The mean threshold value in response to five consecutive stimuli was recorded. Statistical comparisons were made using Student's t test. Results: In the mental region detection thresholds (WDT 1.95±0.9[SD]^oC, CDT 1.04±0.7^oC) were significantly lower than on the tongue (WDT 3.66±3.05^oC p<0.05, CDT 2.46±1.25^oC p<0.001) but pain thresholds were similar in the two areas (mental: WPT 12.55±3.6^oC, CPT 22.7±7.9^oC; tongue WPT 14.78±4.32^oC, CPT 22.48±8.7^oC). There was no significant difference between the thresholds recorded on right or left sides, or after 30 minutes or 1 month. Conclusions: These data reveal differences in thermal detection sensitivity at different sites in the trigeminal region and support the use of contralateral control values for comparison, where appropriate. The results also suggest that, in normal subjects, thresholds are reproducible after both short and long intervals.