Development and Characterization of a Mechanically Induced Temporomandibular Joint Disorder

Routine visits to an orthodontist or dentist for molar extractions or root canals can result in injury to the TMJ or muscles of mastication. The goal of our study was to develop a clinically relevant model of TMD caused by prolonged jaw opening since mechanical overloading of the TMJ is a known causative factor in the onset of osteoarthritis and related orofacial pain disorders. Young male Sprague-Dawley rats were utilized to investigate behavioral and cellular changes in response to prolonged jaw opening. A surgical retractor was placed around the bottom and top incisors and the jaw held at 100% of maximum incisor opening for 20 minutes. Withdrawal responses to mechanical stimuli (up to 2 weeks) were determined following jaw opening. Cytokine levels in the spinal trigeminal nucleus were evaluated using protein antibody microarrays. Statistical analysis was performed using a Mann-Whitney U test with significance considered when p \u3c = 0.05. Maximum jaw opening for 20 minutes was sufficient to cause an increase in sensitivity to mechanical stimuli of V3 trigeminal sensory nerves. Similarly, we found that prolonged jaw opening greatly stimulated expression of numerous cytokines in the spinal trigeminal nucleus at 2 and 24 hours when compared to control animals. Our findings provide evidence that 100% jaw opening for 20 minutes results in sustained sensitization of trigeminal nociceptive neurons by a mechanism that likely involves increased expression of cytokines within the spinal trigeminal nucleus