MMPs in tissues retrieved during surgery from patients with TMJ disorders relate to pain more than to radiological damage score

Abstract

Orofacial pain is among the most common chronic pain conditions and can result from temporomandibular disorders (TMDs) of the temporomandibular joint (TMJ). Matrix metalloproteinases (MMPs) drive degeneration of TMJ tissues and likely mediate pain in TMJ disorders given their role in nociception. However, few studies have assessed MMPs in the TMJ innervated tissues nor in the context of pain. This study defined the extent of MMP‐1, MMP‐9, and MMP‐2 in TMJ tissues from patients undergoing total joint replacement (TJR) or arthroplasty discectomy for painful TMJ disorders. Protein expression was probed by Western blot in TMJ disc and capsular ligaments taken during TJR (n = 6) or discectomy (n = 3) for osteoarthritis or internal derangement in an IRB‐approved study. Pro‐ and active MMP‐1, active MMP‐9, and pro‐ and active MMP‐2 are detectable. MMP‐1 and MMP‐9 correlate positively to each other (Kendall's τ = 0.63; p = 0.01), strengthening the hypothesis that they are mechanistically related in regulatory cascades. Active MMP‐1 and active MMP‐9 correlate positively with self‐reported pain scores (τ ≥ 0.51; p ≤ 0.04), suggesting their involvement in peripheral nociception. Overall, neither MMPs nor pain correlate with the functional vertical opening of the jaw. MMP‐1 varies with the observed stage of degeneration during surgery (p = 0.04). Neither overall MMPs nor pain correlate with the overall magnetic resonance imaging scores, corroborating the longstanding, but confounding, clinical observation that pain and radiological evidence of joint damage are not always related. Clinical significance: These findings suggest that MMPs mediate pain in innervated soft tissues and may be targets for diagnosing disease stage and treatments in painful TMJ disorders.