Protrusive mandibular kinematics in anterior disc displacement: a CT-based 3D motion analysis before and after occlusal splint therapy.

Temporomandibular disorders are associated with altered mandibular mechanics, yet quantitative descriptions of protrusive joint kinematics remain limited. This study quantified protrusive mandibular kinematics in patients with anterior disc displacement with reduction (ADDwR), with and without osteoarthritis (ADDwR&OA), and evaluated changes after occlusal splint therapy using subject-specific three-dimensional analysis. Twenty-four participants were included (12 healthy controls, 6 ADDwR, 6 ADDwR&OA). Mandibular protrusion was recorded using motion capture and integrated with CT-based three-dimensional models. The sagittal condylar guidance angle, range of motion (ROM), finite helical axis (FHA) characteristics, and static and dynamic joint space were analyzed using nonparametric tests with effect sizes. Compared with controls, both patient groups showed a markedly shorter FHA distance (Kruskal-Wallis P < 0.001, ε2 = 0.75), indicating a greater rotational contribution to protrusion, together with a reduced static articular space and dynamic joint space (DJS); the condylar guidance angle and ROM did not differ significantly. After occlusal splint therapy, the articular space and DJS increased and the FHA amplitude decreased-indicating a more stable helical axis-most consistently in the ADDwR&OA group (all P = 0.031), with the largest DJS gained in the lateral eminence, whereas overall protrusive ROM was unchanged. Joint sounds also decreased (11/12 to 5/12 patients; exact McNemar P = 0.031). These findings show measurable, region-specific biomechanical alterations in protrusive mandibular motion in disc displacement, and that occlusal splint therapy is associated with partial restoration of joint space and helical-axis stability (particularly in the more degenerated joints) rather than with changes in gross movement amplitude. Objective kinematic parameters from three-dimensional motion analysis may provide useful adjunctive measures for functional evaluation of temporomandibular joint mechanics.