The myogenic-intrusive hypothesis hypothesis: association between awake clenching and morphometric parameters of the temporomandibular joint. A prospective pilot study protocol

Relevance. Traditional models of temporomandibular joint (TMJ) dysfunction do not explain cases of progressive loss of the vertical dimension of occlusion and TMJ osteoarthritis when tooth crown morphology is preserved. The myogenic-intrusive hypothesis (MIH) proposes that centrally mediated awake clenching causes true intrusion of posterior teeth and TMJ compression. The first step in testing the MIH is to assess the reversibility of joint compression in response to repositioning occlusal therapy. Objective. To present a pilot study protocol designed to assess protocol feasibility, intervention tolerability, and preliminary changes in the width of the superior joint space of the TMJ in patients with daytime masticatory muscle hypertonicity during repositioning occlusal therapy delivered in collaboration with a psychiatrist. Materials and methods. A single-center, prospective, single-arm interventional pilot study is planned (n = 15). Inclusion criteria are age 18–45 years; awake clenching confirmed by electromyography (EMG) using preliminary thresholds for three tests: rest, mouth opening/closing, and maximal clenching; and intact posterior tooth crowns. The intervention consists of a mandibular repositioning occlusal splint made of polymethyl methacrylate, worn around the clock, including during meals. The follow-up period is 6 months. At the end of follow-up, all participants will undergo repeat cone-beam computed tomography (CBCT) of the maxillofacial region and magnetic resonance imaging of the TMJ. The primary endpoint is the change in superior joint space width. Secondary endpoints are changes in EMG activity across the three tests, changes in pain intensity on a visual analog scale, and an exploratory analysis of the association between measures of daytime muscle activity and psychosocial characteristics. This pilot study is not designed to provide definitive evidence of intervention efficacy. Conclusion. The protocol provides a framework for obtaining preliminary data on changes in joint space in response to a repositioning splint and on associations between EMG measures and psychosocial factors. These data will help assess whether a further controlled study of the MIH is warranted.