Sex Difference in Thermal Pain Threshold After Teeth Clenching

Objectives: Oral function such as rhythmical mastication has been reported to suppress pain. Also, as used in a phrase "bear something with clenched teeth", it has long been said that clenching would ease pain. However, the effect of static loading such as teeth clenching on a pain threshold and its sex difference has not been reported yet. The aim of this study was to clarify the sex difference in thermal pain threshold after voluntary clenching.

Methods: Subjects were composed of healthy volunteers (10 males and 10 females, mean age 27.8 yrs). Thermal pain threshold on the right cheek was evaluated using the thermal sensory analyzer (PATHWAY®, Medoc) before and after the 60 seconds maximal voluntary clenching. The thermal stimuli consisted of triplet rapid heat stimuli, triplet slow heat stimuli, and triplet cold stimuli. The data were statistically compared with a student's t-test using SPSS® 15.0J.

Results: In male subjects, thermal pain threshold during rapid heat stimuli significantly increased after clenching (P= .000) while no significant difference was found during slow heat stimuli (P = .371) and cold stimuli (P = .344). In female subjects, no significant changes were observed in thermal pain thresholds after clenching (rapid heat: P = .647, slow heat: P = .740, cold: P = .797).

Conclusions: The results that the thermal pain threshold during rapid heat stimuli increased after clenching in male subjects suggest that the clenching might increase the pain threshold of Aδ fiber only in male subjects. This study was supported by Grant-in-Aids for Scientific Research (B) (No. 19390495) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.