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

Evaluation of the Effects of Occlusal Splint and Masseter Botulinum Toxin Injections on Head and Neck Muscles Using Electromyography

This randomized controlled clinical trial aims to evaluate the individual and combined effects of occlusal splint therapy and botulinum toxin type A (BTX-A) injections into the masseter muscle on the activity of head and neck muscles in patients diagnosed with myofascial pain syndrome (MPS). MPS is a common subtype of temporomandibular disorders (TMD), frequently involving the masticatory and cervical muscles. Despite various treatment modalities, there is still no universally accepted protocol. In this study, 56 adult participants of both sexes, without missing teeth and within a normal body mass index (BMI) range, will be randomly assigned to four groups: BTX-A injection only, occlusal splint only, combined BTX-A and splint therapy, and an untreated control group. Surface electromyography (EMG) will be used to assess muscle activity in the masseter, temporalis, sternocleidomastoid, splenius capitis, and trapezius muscles. EMG recordings will be performed at baseline, 4 weeks, and 12 weeks after the intervention. Pain levels and symptom severity will be assessed using the DC/TMD symptom questionnaire and the Visual Analog Scale (VAS). BTX-A injections will be administered by a neurology specialist (20 IU per masseter muscle), and occlusal splints will be custom-fabricated and fitted for each participant. This study seeks to determine the neuromuscular effects of these treatments-both alone and in combination-on masticatory and cervical muscles and to provide insight into the development of more comprehensive and effective treatment strategies for MPS.

Study Overview

• Status: Recruiting
• Conditions: Masticatory Muscle Pain; Myofascial Pain Syndrome (MPS)
• Intervention / Treatment: Drug: Botulinum toxin injection; Device: Occlusal splint; Combination product: Botulinum toxin + Occlusal splint combined

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 56
• Phase: Phase 4

Contacts and Locations

• Study Contact: Name: Afra Avar, DDS; Phone Number: +905398757502; Email: afraavar@gmail.com

Study Locations

• Turkey
  • Vezneciler
    • Istanbul, Vezneciler, Turkey, 34116
      • Recruiting
      • Istanbul University
      • Contact: Afra Avar, DDS; Phone Number: 05398757502; Email: afraavar@gmail.com
      • Contact: Email: afraavar@gmail.com
      • Principal Investigator: Olcay Şakar, Phd Prof.
      • Sub-Investigator: Afra Avar, DDS
      • Sub-Investigator: Berk Bilgen, Phd

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

1. Having a diagnosis of myofascial pain syndrome
2. No missing teeth
3. No history of previous temporomandibular disorder treatment
4. 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.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Botulinum toxin injection group; Patients will receive a total of 20 units of botulinum toxin injected into the masseter muscle on each side. EMG measurements will be taken before and after treatment to evaluate changes in muscle activity.	Drug: Botulinum toxin injection; Patients will receive a total of 20 units of botulinum toxin type A (Botox) injected into each masseter muscle. The injections will be administered at three standardized sites on each side using a fine needle to ensure accurate delivery. Muscle activity will be recorded using electromyography (EMG) before the injection, and follow-up EMG measurements will be taken at one month and four months post-treatment to evaluate changes in muscle activity and treatment efficacy.
Experimental: Occlusal splint group; Patients will use occlusal splints during sleep. EMG recordings will assess the effect of splint therapy on muscle activity.	Device: Occlusal splint; Patients with myofascial pain syndrome will receive custom-made occlusal splints to wear during sleep. These splints help reduce abnormal muscle activity and relieve pain by redistributing bite forces. EMG measurements will be taken before and during treatment to monitor changes in muscle activity.
Experimental: Botulinum toxin + Occlusal splint combined group; Patients will receive 20 units of botulinum toxin injections into the masseter muscle on each side and use occlusal splints during sleep. EMG will monitor the combined effect on muscle activity.	Combination product: Botulinum toxin + Occlusal splint combined; Patients will receive both botulinum toxin injections (20 units per masseter muscle, injected at three standardized points per side) and will use occlusal splints during sleep. EMG measurements will be conducted before treatment, and at follow-up visits to assess the combined effect of pharmacological and mechanical therapy on muscle activity.
No Intervention: Control group; Patients will not receive any active treatment. EMG measurements will observe natural changes over time.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Electromyography results	Electromyographic (EMG) recordings will be used to assess changes in electrical activity in the masseter, temporalis, sternocleidomastoid (SCM), trapezius, and splenius capitis muscles. These muscles are often overactive in individuals with bruxism, parafunctional habits, and postural issues. Baseline EMG recordings will be taken at week 0, with follow-up measurements at the 1st and 12th weeks to observe short- and mid-term effects. EMG activity in the masseter and temporalis muscles will be evaluated to assess changes following botulinum toxin injections, focusing on potential reductions in muscle hyperactivity. Occlusal splint therapy will be analyzed in terms of its effect on normalizing muscle activity over time. The combined treatment group will be examined for additive or prolonged effects. The control group will serve as a reference to monitor natural variations in EMG activity.	12 week

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Diagnostic Criteria for Temporomandibular Disorders - Clinical Examination Form	Using the DC/TMD Clinical Examination Form, secondary outcomes will be assessed, including the precise location of pain reported by the patients, the characteristics and range of jaw opening movements, as well as the presence and intensity of pain elicited during manual palpation of the masticatory muscles and temporomandibular joint. These evaluations will help to comprehensively understand the functional limitations and pain patterns associated with temporomandibular disorders and will complement the primary outcomes measured in the study.	12 week
Evaluation of Pain and Jaw Function as Secondary Outcomes	As another secondary outcome, pain intensity and jaw functional limitations will be evaluated using a validated pain and jaw function limitation questionnaire. This self-reported tool will allow for the assessment of patients' perceived levels of orofacial pain and the impact of temporomandibular disorders on daily jaw functions such as chewing, speaking, and yawning. These data will support the clinical findings and contribute to a more comprehensive understanding of the functional burden caused by myofascial pain.	12 week

Collaborators and Investigators

• Sponsor: Istanbul University
• Investigators: Study Director: Olcay Şakar, Phd Prof., Istanbul University

Publications and helpful links

General Publications

• Choi KH, Kwon OS, Kim L, Lee SM, Jerng UM, Jung J. Electromyographic changes in masseter and sternocleidomastoid muscles can be applied to diagnose of temporomandibular disorders: An observational study. Integr Med Res. 2021 Dec;10(4):100732. doi: 10.1016/j.imr.2021.100732. Epub 2021 May 16.
• Kaya DI, Ataoglu H. Botulinum toxin treatment of temporomandibular joint pain in patients with bruxism: A prospective and randomized clinical study. Niger J Clin Pract. 2021 Mar;24(3):412-417. doi: 10.4103/njcp.njcp_251_20.
• Yurttutan ME, Tutunculer Sancak K, Tuzuner AM. Which Treatment Is Effective for Bruxism: Occlusal Splints or Botulinum Toxin? J Oral Maxillofac Surg. 2019 Dec;77(12):2431-2438. doi: 10.1016/j.joms.2019.06.005. Epub 2019 Jun 19.

Study record dates

Study Major Dates

• Study Start (Estimated): September 1, 2025
• Primary Completion (Estimated): September 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: July 17, 2025
• First Submitted That Met QC Criteria: July 17, 2025
• First Posted (Actual): July 24, 2025

Study Record Updates

• Last Update Posted (Actual): July 24, 2025
• Last Update Submitted That Met QC Criteria: July 17, 2025
• Last Verified: July 1, 2025

More Information

Terms related to this study

• Keywords: Electromyography; Botulinum Toxin; Bruxism; Masseter muscle; Occlusal Splint; Myofascial Pain Syndrome (MPS); Head and neck muscles; Sternocleidomastoid muscle (SCM); Splenius capitis muscle
• Additional Relevant MeSH Terms: Pain; Neurologic Manifestations; Musculoskeletal Diseases; Nervous System Diseases; Muscular Diseases; Neuromuscular Diseases; Rheumatic Diseases; Musculoskeletal Pain; Fibromyalgia; Myofascial Pain Syndromes; Myalgia; Anti-Infective Agents; Antifungal Agents; Physiological Effects of Drugs; Molecular Mechanisms of Pharmacological Action; Dermatologic Agents; Neurotransmitter Agents; Membrane Transport Modulators; Keratolytic Agents; Cholinergic Agents; Acetylcholine Release Inhibitors; Salicylic Acid; Botulinum Toxins
• Other Study ID Numbers: 2025/150 Rev-1

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No