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.
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
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)
Parallel
upper cervical mobilization
Other interventionUpper cervical mobilization will focus on the atlanto-axial joint. All techniques will adhere to the International Federation of Orthopaedic Manipulative Physical Therapists (IFOMPT) guidelines to minimize the risk of adverse effects 75. Participants will remain in a supine position with their head in a neutral alignment. The physical therapist will apply translatoric mobilization, aligning the transverse process of the atlas (C1) as closely as possible with the transverse process of the axis (C2) in the transverse plane. The intervention will be considered complete once C1 and C2 are properly aligned.
placebo maneuver
Other interventionParticipants will also remain in a supine position with a neutral head posture. However, instead of performing mobilization, the physical therapist will simply place their hands on C1 and C2 without applying any force.
Range of maximum mouth opening as assessed by Zebris Jaw Motion Analyzer device
Data will be presented in millimeters. WinJaw software (Zebris Medical GmbH, Isny, Germany) will be used to collect and calculate the data.
Range of mandibular protrusion as assessed by Zebris Jaw Motion Analyzer device
Data will be presented in millimeters. WinJaw software (Zebris Medical GmbH, Isny, Germany) will be used to collect and calculate the data.
Range of mandibular lateral excursion as assessed by Zebris Jaw Motion Analyzer device
Data will be presented in millimeters. WinJaw software (Zebris Medical GmbH, Isny, Germany) will be used to collect and calculate the data.
Condylar path length as assessed by Zebris Jaw Motion Analyzer device
Data will be presented in millimeters. Data will be collected during mouth opening and closing. WinJaw software (Zebris Medical GmbH, Isny, Germany) will be used to collect and calculate the data.
Cortical excitability of M1 as assessed by Magstim transcranial magnetic stimulator
Resting motor threshold, motor evoked potentials, short-interval intracortical inhibition, and intracortical facilitation of masseter muscle will be collected. LabChart 8 will be used for data collection and statistical analysis.
Maximum tongue pressure values as assessed by wireless tongue pressure measurement device (OCPT-168, Shi-Heng Technology Co. Ltd., Taiwan)
Data will be presented as kPa. The subject was asked to perform the maximum tongue protrusion force that could be exerted.
Self reported masticatory muscle pain intensity as assessed by Visual Analog Scale
Zero is equivalent to no pain, and 10 indicates the worst possible pain.
Upper cervical mobility as assessed by flexion-rotation test at atlanto-axial level
A cervical range of motion device will be used to measure rotation.
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