447: Pain Responses in Temporomandibular Disorders Are Better Described by Effort in a Bruxism Model

Topic: Clinical Science
Subtopic: Pain category (ICD-11), Chronic primary musculoskeletal pain, Electrophysiology, Assessment and Measurement of Pain/Nociception, Quantitative Sensory testing (static and dynamic, e.g., HPT, PPT, CPM, TSP, offset analgesia)

Background and Aims: Sleep bruxism is commonly quantified by the number of electromyographic events; however, event counts may not adequately represent cumulative muscular load or the clinical impact of repetitive jaw activity. Experimental tolerance tests and non-standardized clenching tasks have improved understanding of muscle pain mechanisms but often fail to reproduce the intermittent, rhythmic, and load-dependent characteristics of bruxism activity. Based on polysomnographic definitions of rhythmic (phasic) and sustained (tonic) activity, this study investigated discomfort and pain responses in women with and without temporomandibular disorders (TMD) using a standardized intermittent clenching model designed to approximate clinically relevant bruxism-related mandibular loading.

Methods: Fifty-six women (control = 27; TMD = 29) performed clenching tests using EMG-guided trajectories calibrated to maximum voluntary contraction. Tasks were designed as an experimental bruxism model incorporating phasic contractions (2s rhythmic bursts) and tonic contractions (>2s sustained activity). Six randomized conditions combined contraction type and intensity (15%, 30%, 45% MVC) over 120 seconds. Tasks were also matched by muscular load (area under the curve) at two points, mild and moderate physiological effort. Pressure pain thresholds were measured pre- and post-task, while pain ratings (VAS) were recorded before, during, and after. Between-group and repeated-measures comparisons were conducted at a 5% significance level.

Results: Standardized clenching induced discomfort and occasional mild pain in both groups. Women with TMD presented higher baseline and post-task pain and lower pressure pain thresholds, indicating increased peripheral sensitivity. Pain increased with time and contraction intensity, with high-intensity tonic contractions producing greater discomfort. Although contraction type, intensity, and duration influenced pain perception, same muscular load did not effected VAS scores between tasks (all p>0.05), while comparisons between mild and moderate effort were significant for all tasks (p<0.05). Despite equivalent load exposure, the TMD group maintained higher pain ratings, suggesting residual hypersensitivity beyond mechanical load.

Conclusions: This adapted experimental bruxism model provides a physiological paradigm that approximates intermittent mandibular loading observed in sleep bruxism. While contraction type, intensity, and duration influence pain perception, cumulative muscular load aligned responses across tasks and did not alter overload detection by VAS. Women with TMD exhibited amplified responses even under equivalent load, supporting peripheral sensitization mechanisms. These findings suggest that cumulative load exposure may be more clinically meaningful than event counts alone and support incorporating load-based metrics, such as area under the curve, in future polysomnographic analyses of bruxism-related muscle activity.

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Presenting Author: Tatiana Prosini da Fonte
Submitting Author: Tatiana da Fonte

Senior Author: Paulo César Rodrigues Conti

IASP 2026 Global Year theme of Neuropathic Pain: No

• Matheus Herreira-Ferreira: PhD - University of São Paulo
• Carolina Ortigosa Cunha: PhD - University of São Paulo
• Juliana Stuginski-Barbosa: PhD - Instituto de Ensino Odontológico - IEO
• 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