• Takuya Naganawa, Lene Baad-Hansen, Tomohiro Ando, and Peter Svensson.
• Section of Clinical Oral Physiology, Department of Dentistry, Health, Aarhus University, Vennelyst Boulevard 9, 8000, Åarhus C, Denmark, tanaganawa@gmail.com.
• Exp Brain Res. 2015 Apr 1;233(4):1189-99.

AbstractThe aim of this study was to investigate temporal and spatial aspects of somatosensory changes after topical application of capsaicin, menthol and local anesthetics (LA) on the gingiva with the use of intraoral palpometers and thermal devices. Sixteen healthy volunteers (eight male, eight female) participated. Four topical preparations (capsaicin, menthol, LA and Vaseline as a control) were randomly applied to the gingiva around the first premolar in the upper jaw via individual oral templates, which allowed spatial mapping of somatosensory changes at and adjacent to the site of application. The topical drugs were applied for 15 min in a randomized and balanced sequence. The perceived preparation-evoked pain intensity was recorded with the use of 0-10 visual analog scales (VAS). Standardized mechanical and thermal stimuli were applied before, during and up to 30 min after the topical applications, and numerical rating scales (NRS) were used to score the perceived intensity of the stimuli. Peak VAS, area under the curve and mean VAS preparation-evoked pain scores for capsaicin, menthol, LA and control were compared with paired t tests. NRS scores for mechanical and thermal test stimuli were analyzed with four-way repeated measurements analyses of variance. Capsaicin evoked significantly higher VAS pain parameters as well as higher NRS scores to heat stimuli than control (P < 0.029). There were no significant differences in stimulus-evoked NRS scores between the menthol and control conditions (P = 0.518), but LA caused significantly lower stimulus-evoked NRS scores compared with control (P < 0.001). Post hoc tests showed that capsaicin caused sensitization to heat stimuli at and adjacent to the application area. In conclusion, this study for the first time demonstrates the time course of capsaicin-evoked heat hyperalgesia in and outside the site of application at the oral mucosa (primary and secondary hyperalgesia).

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