TMJ hyperextension is associated with sustained nociception and dysfunction of pain modulation pathways in female rats

Objective: Temporomandibular Disorders (TMDs) are debilitating orofacial pain conditions caused by extrinsic or intrinsic injury to the temporomandibular joint (TMJ) with higher prevalence reported in women.  Changes in innociception, protein expression, and joint structure were investigated in a preclinical TMD model caused by TMJ hyperextension in male and female rats. Methods: Mechanical nociception was determined using von Frey filaments, protein expression investigated by immunohistochemistry, synovial levels of TNF-α and IL-6 by ELISA, and TMJ morphology by micro-computed tomography.  Results: Only female rats exhibited enhanced nociception and TMJ guarding behavior.  TMJ hyperextension increased expression of proteins implicated in ascending pain signaling and modulation of proteins associated with the descending pain inhibitory pathway.  TNF-α levels were elevated in males and females, while IL-6 was only increased in males. No changes in bone morphology were observed.  Conclusion: Our findings provide evidence of sexual dimorphism in a novel TMD model caused by a single, transient hyperextension event.