Influence of intra- and extraoral sites and size of stimulation area on thermal detection and pain threholds. A methodological study

Aim: This study compared cool detection thresholds, warm detection thresholds and heat pain thresholds at intra- and extraoral locations and measured the influence of spatial summation. Material and Methods: Thirty healthy individuals (15 females and 15 males), mean age 24.9 years, range 20-31 years) participated in the study. Thresholds for warm detection (WDT), cool detection (CDT) and heat pain threshold (HPT) were measured using a thermotester (MSA–Modular sensory Analyzer, Somedic). The intraoral thermode was custom-made with a 9x9mm square surface. The average of three measurements was recorded. Four intraoral sites (gingival regions 24 and 34, tip of the tongue, lower lip) and two extraoral sites (infraorbitalis, thenar) were measured in each participant. To measure spatial summation, five acrylic covers (tip areas: 0.81 cm2, 0.50 cm2, 0.28cm2, 0.125cm2, 0 cm2) were made to fit the thermode. Five measurements on the tip of the tongue were averaged for each acrylic cover. Results: Of the extraoral sites, the cold detection threshold was significantly higher and the heat pain threshold was significantly lower at the infraorbitalis than at the thenar. Of the intraoral sites, the cold detection threshold was significantly lower at the tongue than at any of the other intraoral locations; the heat pain threshold was significantly lower on the tip of the tongue than on the lower lip. Warm detection and heat pain thresholds rose slightly with increasing thermode size, and this association was more pronounced than for cold detection thresholds. Conclusion: Temperature thresholds differed significantly between several anatomic sites, and the association between size of stimulation area and temperature thresholds was weak