Mandibular Exercises and Conditioned Pain Modulation in Women With Temporomandibular Disorders

Objectives: Jaw Exercices has been proven as a pain relief therapy for Myofascial Pain. Conditioned Pain Modulation (CPM) determines how an endogenous inhibitory system regulates pain sensation. Our purpose was to investigate Conditioned Pain Modulation as a possible mechanism of exercise induced analgesia and its behavior in women with Myofascial Pain.
Methods: A double-blind randomized controlled trial was performed. 25 women with myofascial pain (RDC/TMD) were randomly assigned to a daily isometric (n = 9) or isotonic (n = 6) jaw exercise for 21 days. 9 women were followed as a neutral control group for the same time. Masseter, Temporal and forearm muscles pressure pain threshold (PPT) and pressure pain tolerance (PPTol) and VAS were measured on days 1, 7, 14 and 21 at baseline and after a conditioning stimuli. Cold water arm immersion was used as a noxious stimuli to calculate CPM. Variations between each week were analyzed with SPSS® and SYSTAT® software by Kolmogorov Smirnov, Scheffe,Chi² ,ANOVA and t tests, Bonferroni correction and linear regression. This study was performed under IASP ethical guidelines for pain research in humans and was approved by the local ethics committee.
Results: Pain modulation varied in all three groups within 21 days. Only after 21 days Isometric exercises had a positive correlation with CPM, improving modulatory response and decreasing pain perception (p=0.01). Subjective pain improves (p=0.00) and some PPT and PPTol thresholds tended to fluctuate in different days, (p<.05). The control group muscles had an inconstant behavior over time, decreasing pain perception at day 21.
Conclusions: CPM varies over time and is related with pain perception after a 21 day jaw exercise therapy, which may improve subjective and mechanic pain perception. These results cant explain conditioned pain modulation as exercise induced analgesia mechanism. We suggest to continue studying this mechanism.