489: Isometric Masticatory Endurance and Electromyographic Data in Myogenous Temporomandibular Disorders

Topic: Clinical Science
Subtopic: Pain category (ICD-11), Chronic primary orofacial pain, Electrophysiology, Assessment and Measurement of Pain/Nociception

Background and Aims: Understanding muscle function in individuals with chronic musculoskeletal pain has been a research focus for decades; however, important aspects remain unclear. Temporomandibular disorders (TMD) comprise a group of conditions affecting the temporomandibular joint, masticatory muscles, and associated structures. Symptoms such as fatigue, discomfort, stiffness, and pain are frequently reported, particularly in myogenous TMD, the most prevalent subtype. Given its high clinical frequency, it is important to clarify whether TMD alters muscle performance compared to healthy individuals. This study aimed to evaluate electromyographic (EMG) parameters during a masticatory isometric endurance task (MIET) in women with TMD compared to healthy controls.

Methods: This study was approved by the local ethics committee. Fifty-six women (27 controls, 29 TMD) were included according to eligibility criteria. All participants performed an MIET sustaining a contraction at 33% of maximum voluntary bite force (MVBF) with visual feedback, until fatigue or pain prevented continuation. Surface single-channel EMG (Neurobots, Recife, Brazil) recorded normalized RMS (uVRMS), uVRMS slope, coefficient of variation (CoV), endurance time, and MVBF. Pain/discomfort intensity was assessed using a visual analog scale (VAS). Between-group comparisons were conducted at a 5% significance level.

Results: Three participants were excluded for not completing 30 seconds, resulting in 53 individuals (26 controls, 27 TMD). No significant between-group differences were found in EMG parameters (p>0.05). VAS scores were higher in the TMD group both before (p<0.001) and after (p=0.008) the MIET; however, pain change (ΔVAS) did not differ between groups (p>0.05). Both groups demonstrated increased CoV in the final quartile (p<0.001) and a negative normalized uVRMS slope (-0.002 uVRMS/s), suggesting EMG fatigue. MVBF decreased post-task in controls (p<0.001). Task interruption due to pain was more frequent in TMD (p=0.004).

Conclusions: Both groups exhibited EMG fatigue following the isometric task, with no significant differences in objective muscle parameters. These findings suggest that myogenous TMD may not substantially impair masseter performance under controlled isometric loading in women. However, women with TMD demonstrated greater baseline and post-task pain perception and were more likely to interrupt the task due to pain, indicating increased subjective vulnerability during demanding motor tasks despite similar objective muscle responses.

References: 1. Christensen LV. Some electromyographic parameters of experimental tooth clenching in adult human subjects. J Oral Rehabil. 1980;7(2):139-46.

2. Dao TTT, Lund JP, Lavigne GJ. Pain responses to experimental chewing in myofascial pain patients. J Dent Res. 1994;73(6):1163-7.

3. Clark GT, Beemsterboer PL, Jacobson R. The effect of sustained submaximal clenching on maximum bite force in myofascial pain dysfunction patients. J Oral Rehabil. 1984;11(4):387-91.

4. Lund JP, Donga R, Widmer CG, Stohler CS. The pain-adaptation model: a discussion of the relationship between chronic musculoskeletal pain and motor activity. Can J Physiol Pharmacol. 1991;69(5):683-94.

5. Stanisic N, Baram S, Nykänen L, List T, Bracci A, Svensson P, et al. Exploring the relationship between muscle activity, jaw behaviour and pain. Sci Rep. 2025;15(1):35029.

6. Enoka RM, Duchateau J. Muscle fatigue: what, why and how it influences muscle function. J Physiol. 2008;586(1):11-23.

Presenting Author: Matheus Herreira-Ferreira
Submitting Author: Matheus Herreira-Ferreira

Senior Author: Paulo César Rodrigues Conti

IASP 2026 Global Year theme of Neuropathic Pain: No

• Tatiana Prosini da Fonte: PhD - University of São Paulo
• Juliana Stuginski-Barbosa: PhD - Instituto de Ensino Odontológico
• Carolina Ortigosa Cunha: PhD - UNISAGRADO
• Leonardo Rigoldi Bonjardim: PhD - University of São Paulo
• Estephan Jose Moana-Filho: PhD - University of Minnesota
• Paulo César Rodrigues Conti: PhD - University of São Paulo