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

Abstract 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.