Finite element evaluation of unilateral distraction splints: implications for temporomandibular joint loading patterns.

Although once widely used in temporomandibular disorder (TMD) therapy, unilateral distraction splints (DSs) have raised concern for generating compressive rather than distractive effects on the temporomandibular joint (TMJ). This finite element analysis investigated the biomechanical behavior of two unilateral splint designs (DS7 and DS567) in a healthy TMJ model, focusing on the influence of ipsilateral masseter force and capsular stiffness. Cone-beam computed tomography data from a healthy adult were used to create anatomical models and unilateral clenching was simulated under three levels of ipsilateral masseter force and three capsule stiffness conditions (baseline, - 5%, - 10%). Condylar and disc stress and displacement responses were calculated using nonlinear static analysis. Increasing ipsilateral masseter force markedly elevated both condylar and disc displacement, with the DS7 design producing approximately 60% higher disc and 30% higher condylar movement than DS567. Decreasing capsular stiffness yielded only minor additional displacement (< 2.5%). In all simulations, both condyles moved predominantly in a superior, compressive direction, with contralateral structures consistently exhibiting greater von Mises stress peaks ~ 1.2 MPa in the posterior-medial disc and ~ 1.0 MPa on the anterior condylar surface. Masseter muscle force was the dominant determinant of joint loading, whereas capsular stiffness had a minor effect. Broader splint coverage reduced stress and displacement, suggesting a role of splint geometry in modulating load transmission. These findings provide model-based insight into the unilateral DSs, suggesting predominantly compressive rather than distractive joint responses, under simulated conditions.