A Human Model of Intraoral Pain and Heat Hyperalgesia

Aim: To examine, in a double-blind and placebo-controlled crossover manner, the effect of topical application of capsaicin on the alveolar mucosa with a battery of intraoral quantitative sensory testings (QST) in 16 healthy volunteers. Methods: Thirty µL of 5 mg/mL capsaicin or vehicle (control) was applied to a 3 x 3- mm paper disk and applied to the alveolar mucosa under an oral bandage. The subjects rated the perceived pain intensity on a 0 to 10 electronic visual analog scale (VAS) for 15 minutes. Quantitative sensory testings were performed before and immediately after the 15-minute application and consisted of assessments of cold detection threshold, warmth detection threshold (WDT), cold pain threshold, heat pain threshold (HPT), mechanical sensitivity to single and repeated punctate mechanical stimulation with von Frey filaments and to single and repeated brush stimulation with a cotton swab, and detection and pain thresholds to electrical stimulation of the alveolar mucosa and maxillary first premolar tooth. Analysis of variance was used to test the data. Results: Application of capsaicin caused moderate levels of pain (VASpeak scores 5.0 ± 1.9) whereas the vehicle was practically painless (VASpeak 0.9 ± 2.4). No significant effects of vehicle on QST could be detected (P > .143). In contrast, capsaicin application was associated with significant decreases in WDT and HPT (P .001). No other significant changes in QST were observed for capsaicin application. Conclusion: The intraoral capsaicin pain model is associated with signs of heat hyperalgesia, but not mechanical hyperalgesia. Since the somatosensory sensitivity is not well characterized in most orofacial pain conditions, mainly due to lack of tradition and techniques, intraoral QST may provide a better description of the somatosensory sensitivity and underlying mechanisms in orofacial pain conditions. Keywords: capsaicin, hyperalgesia, orofacial pain, pain measurement