EMG-Based Evaluation of Occlusal Splint and Masseter Botox Effects on Head and Neck Muscles

This study is a prospective, randomized, controlled, parallel-group clinical trial designed to investigate the effects of occlusal splints and BTX-A injections in adult patients with myofascial pain syndrome (MPS), as diagnosed by the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). A total of 56 adult participants (both male and female) will be recruited and randomly divided into four equal groups (n=14): (1) BTX-A injection only, (2) occlusal splint only, (3) BTX-A combined with occlusal splint, and (4) control group receiving no treatment. All participants must be within the normal BMI range and have complete dentition.

Exclusion criteria

include pregnancy or lactation, systemic neuromuscular or bleeding disorders, prior BTX-A treatment in the masseter region, recent facial aesthetic procedures, and any condition that may hinder study compliance.

BTX-A will be injected into the masseter muscles at three standardized sites per side (total 20 IU per muscle) using a 1 ml syringe with a 26-gauge, 13 mm needle. The injections will be performed by a neurologist in a hospital setting. For participants in the occlusal splint group, upper jaw impressions will be taken using alginate, and splints will be fabricated from 2 mm thick hard vinyl acetate sheets. Splints will be positioned intraorally with autopolymerizing acrylic resin to ensure consistent fit and occlusal contact.

EMG measurements will be conducted at Bezmialem Vakıf University using surface electrodes placed over the masseter, temporalis, sternocleidomastoid, splenius capitis, and trapezius muscles. The skin will be cleaned with 70% alcohol, and electrode placement will follow anatomical landmarks. Recordings will be obtained during maximal voluntary clenching with participants seated and relaxed. Measurements will be taken before treatment, at 4 weeks, and at 12 weeks post-intervention to monitor short- and long-term effects.

All patients will complete the DC/TMD symptom questionnaire and rate their pain using a Visual Analog Scale (VAS) at each time point. Statistical analysis will be performed using SPSS v22. Parametric and non-parametric methods will be applied based on data distribution. Intergroup comparisons will be performed using one-way ANOVA or Kruskal-Wallis tests, and intragroup comparisons will utilize repeated measures ANOVA or Friedman tests. Chi-square tests will be used for categorical data. A significance level of p<0.05 will be considered statistically meaningful.

The study was approved by the Clinical Research Ethics Committee of Istanbul University Faculty of Dentistry and will be funded by the university (BAP). All procedures will be carried out under professional supervision to ensure safety and reliability of data collection.

Inclusion criteria

• Having a diagnosis of myofascial pain syndrome
• No missing teeth
• No history of previous temporomandibular disorder treatment
• Absence of an arthrogenic temporomandibular disorder

Exclusion criteria

• Pregnancy or lactation; osteoporosis and bisphosphonate use
• Previous botulinum toxin injection to the masseter region
• Bleeding disorders or use of anticoagulant medications
• Presence of systemic muscular or neurological diseases (e.g., myasthenia gravis, ALS)
• Active infection, open wound, or dermatological condition in the facial area
• Undergoing other facial aesthetic procedures (e.g., fillers, PRP, etc.) within the last six months
• Individuals with severe psychiatric disorders or those on regular psychiatric medications
• Patients who are unlikely to comply with the study protocol or complete the follow-up period
• Individuals with a body mass index (BMI) outside the normal range, including underweight or overweight participants, will be excluded from the study.