Volume and morphological characteristics of masticatory muscles in patients with unilateral disc displacement without...

The temporomandibular joint (TMJ) functions as an integrated unit, therefore pathology affecting one side may affect the other. This cross-sectional study aimed to evaluate the effect of unilateral disc displacement without reduction (DDWoR) on the volumes of three masticatory muscles. Additionally, it investigated the relationship between lateral pterygoid muscle (LPM) attachment type, its volume and DDWoR.

A total of 84 TMJ MRI samples were analyzed. The control group consisted of 44 TMJ MRI samples, obtained separately from both TMJs of 22 bilaterally healthy individuals. The study group included 20 patients with unilateral DDWoR; MRI samples of unaffected TMJs formed the first study group (n = 20) and MRI samples of the affected TMJs formed the second study group (n = 20). In all groups, the LPM, masseter (MM), and medial pterygoid (MPM) muscle volumes were measured and LPM attachment types were classified. One-way ANOVA, Fisher's Exact and Chi-square tests were applied, while MANCOVA assessed the effects of gender, age and body-mass index (BMI) on muscle volume and the estimated marginal means were calculated accordingly.

The MM volume was significantly higher in the control group compared to study groups (p = 0.002), with no difference between the two study groups (p = 1.000). LPM (p = 0.688) and MPM (p = 0.348) volumes showed no significant differences between groups. No casual relationship was identified between LPM attachment type and DDWoR (p = 0,981). Type-III attachment was associated with higher muscle volume.

Unilateral DDWoR may affect MM morphology, highlighting the importance of evaluating masticatory muscles during treatment planning. Additionally, reduced MM volume may serve as a marker in the clinical diagnosis of DDWoR.