Effects of Cervical Manual Therapy for Temporomandibular Disorders With Myalgia

Background: Temporomandibular disorders (TMDs) are the leading cause of non-odontogenic orofacial pain interfering with daily activities. TMDs consist of a group of conditions affecting the masticatory muscles, the temporomandibular joint (TMJ), or the associated structures. Previous studies showed alterations in TMJ kinematics, cortical excitability, electromyographic (EMG) activity of the masticatory muscles, and tongue pressure in individuals with TMDs compared to healthy controls. Furthermore, several studies have demonstrated that manual therapy applied to the cervical joint could reduce pain and improve jaw function in individuals with TMDs. However, the effects of upper cervical mobilization on TMJ kinematics, cortical excitability, tongue pressure, and EMG of masticatory muscles during mouth opening in individuals with myogenous TMDs remain unknown. Purpose: This study aims to investigate the immediate effects of upper cervical mobilization on TMJ kinematics, EMG of masticatory system muscles, cortical excitability, and tongue pressure in individuals with myogenous TMDs. Methods: A randomized controlled trial will be conducted with a total sample size of 48 participants. Individuals diagnosed with myogenous TMDs, defined as chronic myalgia (lasting \>3 months continuously or \> 6 months intermittently) according to the Diagnostic Criteria for Temporomandibular Disorders, will be recruited for this study. Participants will be randomly assigned to either the experimental or the control group, stratified by age and sex. The experimental group will receive a single session of upper cervical mobilization, while the control group will receive a placebo maneuver. The primary outcomes will include TMJ kinematics and EMG activity of the masseter and suprahyoid muscles, while the secondary outcomes will include cortical excitability, tongue pressure, pain intensity, and upper cervical mobility. All measurements will be taken before and immediately after the intervention. Statistical analysis: The continuous and categorical variables of clinical and demographic characteristics will be analyzed by an independent t test/Mann-Whitney U test and a Chi-square test, respectively. A 2×2 mixed-model analysis of variance (ANOVA) will be used to analyze the outcome measures and to test the main effects and interactions between time and group. If there is a significant interaction effect, post hoc pairwise comparisons with Bonferroni correction will be used. The alpha level is set at 0.05.

Inclusion Criteria: * Diagnosed with myogenous TMDs, defined as chronic myalgia (lasting \>3 months continuously or \> 6 months intermittently) 90 with or without accompanying arthralgia according to DC/TMD criteria * A visual analogue scale (VAS) score of 3 or greater at baseline * 18 to 60 years of age Exclusion Criteria: * Diagnosed with disc displacement without reduction or degenerative joint disease according to the DC/TMD criteria * A diagnosis of systemic diseases such as fibromyalgia, rheumatoid arthritis, systemic erythematous lupus, or psoriatic arthritis * A diagnosis of neurological disorders (e.g., trigeminal neuralgia, cervical radiculopathy, or myelopathy) * Evidence of central nervous system involvement (positive pathological reflexes) * A history of traumatic injuries (e.g., contusion, fracture, or whiplash injury) in the last 6 weeks * Signs of vertebral artery insufficiency or upper cervical instability revealed by physical examination * Receiving cervical spine mobilization or manipulation or acupuncture for their TMDs within the last 1 week * any contraindication to TMS