Does Temporomandibular Joint Disc Displacement Influence Joint Space Dimensions, and Does Sex Play a Role?

Joint space dimensions influence maxillomandibular relationships by altering condylar position. Although disc displacement (DD) is the most common temporomandibular joint (TMJ) disorder, its effect on joint space dimensions and associated morphology remains unclear.

This study aimed to determine whether DD status and sex are associated with differences in joint space dimensions and related bony morphology, based on combined TMJ magnetic resonance imaging and computed tomography (CT) evaluations.

This retrospective cross-sectional study included patients who underwent paired magnetic resonance imaging and CT scans at Seoul National University Dental Hospital between 2008 and 2023. Exclusion criteria were congenital anomalies, systemic diseases, previous TMJ, orthodontic or orthognathic treatment, and trauma involving the TMJ.

The predictor variables were 1) DD status, categorized as normal disc position (NR), DD with reduction, and DD without reduction and 2) sex, coded as male or female.

The main outcome variable was joint space dimensions, selected for their influence on condylar position, including sagittal (anterior, superior, and posterior) and coronal (medial, central, and lateral) joint space distances (mm), and anterior, superior, posterior, and total joint space volumes (mm³).

Age, CT modality (cone-beam CT vs multidetector CT), and laterality (right vs left) were considered as potential covariates.

Linear mixed-effects models with a subject-level random intercept were applied, with Bonferroni and false discovery rate adjustments. Statistical significance was set at P < .05.

The sample consisted of 85 subjects (24.6 ± 6.8 years), including 41 males (48.2%) and 44 females (51.8%). Age, CT modality, and laterality did not affect outcomes (P > .05). Compared with NR joints, DD joints exhibited a smaller condyle within a larger fossa (P < .05) and significantly greater anterior joint space distance in the sagittal plane, without differences in superior or posterior distances (P = .108 and P = 0.913, respectively). Coronal joint space distances did not show differences (P > .40). Anterior joint space volume was larger in DD joints than in NR joints (P < .001). Sex did not significantly influence these associations (P > .05).

DD is associated with smaller condyles and enlarged fossa, contributing to increased anterior joint space dimensions. These findings may aid diagnosis and treatment planning in patients with TMJ DD.