Association of posterior occlusal support with ultrasonographic characteristics of the masseter muscle: a prospective single-center study.

BACKGROUND: Posterior occlusal support is associated with masticatory loading, but its relationship with masseter morphometry, a derived strain-elastography metric, and processed B-mode image texture has not been fully characterized. This observational study evaluated the association of posterior occlusal support, classified by the Eichner index, with masseter muscle thickness, estimated masseter volume, a derived strain-elastography metric, and B-mode image-texture fractal dimension in systemically healthy adults using a multimodal ultrasonographic protocol. METHODS: Of 112 enrolled systemically healthy individuals, four did not complete the ultrasonographic protocol; 108 participants (56 female, 52 male; mean age 51.12 ± 12.30 years) were analysed and classified as Eichner group A (n = 44), B (n = 43), or C (n = 21). Bilateral masseter thickness, estimated masseter volume, and a derived strain-elastography metric were assessed at rest and during non-force-standardized maximum voluntary clenching; resting B-mode image-texture fractal dimension was calculated from processed ultrasonographic images. Group comparisons, paired analyses, correlation analyses, and generalized estimating equation models were performed. RESULTS: Thickness, estimated masseter volume, and the derived strain-elastography metric were higher during clenching than at rest (all p < 0.001). Thickness and estimated masseter volume were lower from Eichner A to C under both conditions (all p < 0.001). In exploratory analyses, the derived strain-elastography metric was higher in group A than in groups B and C, and resting B-mode image-texture fractal dimension was lower from A to C (p < 0.001). Adjusted between-group differences in rest-to-clench change were most consistent for thickness; interactions for estimated masseter volume and the derived strain-elastography metric were model dependent. CONCLUSIONS: Reduced posterior occlusal support was associated with lower masseter thickness, lower estimated masseter volume, lower derived strain-elastography metric values, and smaller rest-to-clench changes, most consistently for thickness. Exploratory findings for B-mode image-texture fractal dimension also differed across Eichner groups but require validation using acquisition-standardized imaging.