Mandibular Opening Kinematic Simulation in the Temporomandibular Joint at Defined Angles

The pathogenesis of temporomandibular disorders (TMD) stems from the biomechanical coupling of osseous structures, articular disc viscoelasticity, and muscular coordination. This study established a high-fidelity 3D temporomandibular joint (TMJ) model to systematically quantify the dynamic displacement inhibition mechanism of disc degeneration during staged mandibular opening. Three biomechanically distinct phases were analyzed: initial rotation-dominant phase (5°), transitional phase (12.5°), and terminal translation-dominant phase (20°). Progressive disc degeneration was simulated by modulating elastic modulus (10–150 MPa) and Poisson's ratio (0.4–0.25). Results revealed a phase-dependent cumulative inhibition effect: terminal-phase condylar displacement suppression (5.58%–13.1%) exceeded initial-phase values by 3.6-fold, while incisal point inhibition increased from 1.37%–4.63% (initial) to 5.01%–11.8% (terminal). Crucially, bilateral coordination stability (DL-R fluctuation <0.001 mm) persisted across all phases despite exponentially amplified displacement constraints, indicating TMJ's compensatory optimization of force transmission. These findings establish a critical threshold (12.5° opening angle) for accelerated degradation effects and provide biomechanical criteria for TMD staging and early intervention.