Integrated Multilevel Analysis of Surface Electromyography to Analyse Neuromuscular Patterns in Temporomandibular Disorders

BACKGROUND: Surface electromyography (sEMG) has been proposed as a non-invasive tool to evaluate masticatory function in patients with temporomandibular disorders (TMD). However, functional indices remain insufficiently characterised. OBJECTIVE: To compare sEMG indices among myogenous and arthrogenous TMD and healthy subjects and explore their relationships. METHODS: This cross-sectional study included 116 myogenous, 68 arthrogenous and 25 healthy subjects. Surface Muscle Index (SMI), Percentage Overlapping Coefficient of anterior temporalis (POC TA) and of masseter muscles (POC MM), Barycentre (BAR), Torsion (TORS), IMPACT and asymmetry were analysed. Kruskal-Wallis tests were used, followed by Dunn's post hoc tests with Holm correction. Effect sizes were estimated using eta-squared based on the H statistic. Directional and status-based categorical variables were compared using chi-square or Fisher's exact tests. Inter-metric associations were explored using Spearman correlation coefficients and exploratory principal component analysis (PCA). RESULTS: Only SMI and BAR showed significant between-group differences (Holm-corrected p = 0.007 and p = 0.001, respectively), with lower values in the myogenous group. IMPACT showed a borderline association with the group (p = 0.052). Categorical analyses revealed significant between-group differences for POC TA side and torsional predominance and IMPACT status. Correlation analysis showed that SMI was strongly associated with BAR (r = 0.83) and TORS (r = 0.74), suggesting a functional organisation. CONCLUSIONS: SMI and BAR were informative for characterising group-level functional differences, particularly those involving the myogenous group. Selected categorical functional patterns, particularly torsional and IMPACT status, differed across groups. These findings support the potential of sEMG metrics in functional characterisation of TMD phenotypes, particularly in myogenous TMD.