Contralateral disc loading in unilateral temporomandibular joint disc displacement without reduction: A finite...

Unilateral temporomandibular joint (TMJ) disc displacement without reduction (DDwoR) alters joint biomechanics, but its mechanical impact on the contralateral disc remains unclear.

The purpose of this clinical study was to evaluate stress distribution patterns in the contralateral TMJ disc during mandibular function in unilateral DDwoR using 3-dimensional (3D) finite element analysis (FEA).

Two patient-specific 3D TMJ models were reconstructed from computed tomography and magnetic resonance imaging: Model-N (bilaterally normal discs) and Model-D (unilateral right-sided DDwoR). Each model included bilateral joints. Mandibular opening, closing, and lateral excursions were simulated. In Model-D, a 5-mm deviation toward the affected side was incorporated to reproduce functional asymmetry. FEA was used to estimate disc stress distributions not directly measurable in vivo. von Mises stress values were calculated for the anterior, intermediate, and posterior disc regions.

In the DDwoR model, contralateral disc stresses were consistently higher than those in the healthy model across all movements, with the highest peak observed during mouth opening (144.8 MPa, intermediate zone). Right lateral excursion toward the affected side increased stress in the contralateral intermediate zone (13.0 MPa), whereas the affected disc showed maximum loading in the posterior zone (33.2 MPa). Mandibular deflection was associated with higher contralateral intermediate zone stresses compared with symmetric mouth opening.

Unilateral DDwoR led to marked compensatory stress increases in the contralateral disc, most prominently during mandibular opening.