Ultrasound examination of asymmetry in temporomandibular disorders

Ultrasonography is a non-invasive, radiation-free, and cost-effective imaging modality for evaluating the Temporomandibular Joint (TMJ) and Masticatory Muscles (MM). Despite its clinical potential, a standardized quantitative ultrasound protocol for assessing masticatory system asymmetry in Temporomandibular Disorders (TMD) is lacking. This pilot study aimed to evaluate the feasibility of a standardized ultrasound protocol for the quantitative assessment of masticatory system asymmetry and to explore its preliminary associations with TMD-related symptoms.

Fifteen young adult participants (aged 19-26 years) underwent bilateral ultrasound examination of the masticatory muscles (masseter, temporalis, lateral pterygoid, and sternocleidomastoid muscles) and TMJ structures, including interarticular spaces and articular components. Measurements were performed by trained examiners using standardized anatomical landmarks. Asymmetry was quantified using percentage difference indices and aggregated into a composite anatomical asymmetry score. Proposed asymmetry reference values were applied for descriptive purposes only, and all statistical analyses were conducted on an exploratory, hypothesis-generating basis.

The composite anatomical asymmetry index differed from symmetry (mean ± SD: 18.45% ± 17.13%). An association was observed between anatomical asymmetry and joint sounds (crepitation) (Spearman's ρ = 0.88), while pain showed a lower-magnitude association (ρ = 0.51).

This pilot study demonstrates the feasibility of a standardized ultrasound-based protocol for the quantitative assessment of masticatory system asymmetry. The findings are exploratory and intended to support methodological development and hypothesis generation. Further validation in larger, blinded study populations is warranted.