Finite element analysis of TMJ disc and PDL stress in mandibular advancement device therapy for OSA

To establish patient-specific three-dimensional finite element analysis (FEA) models to investigate the effects of different mandibular advancement distances and vertical opening ranges of a mandibular advancement devices (MADs) on the stress distribution within the temporomandibular joint (TMJ) disc and the periodontal ligament (PDL) of the lower anterior teeth during the treatment of obstructive sleep apnoea (OSA), and to identify a biomechanically favourable parameter window.

A high-precision three-dimensional FEA model was constructed, encompassing the "TMJ disc-maxilla-mandibular advancement device" system. The Powell truss method was used to calculate condylar rotation, and the maximum mandibular advancement distance was fixed at 8mm. An orthogonal experimental design was employed to generate a total of 25 variable combinations. FEA was performed for each combination to analyse the stress distribution within the TMJ disc and the PDL of the lower anterior teeth.

As the mandibular advancement distance increased from 50 to 70%, the peak stress in TMJ discs rose by 265% and the peak stress in the PDL increased by 179%. For every 7.07% increase in mandibular advancement distance, stress in the TMJ discs increased by 1.335MPa. However, when the vertical opening distance exceeded 5mm, the rate at which PDL stress increased with mandibular advancement distance slowed. The computational analysis suggested that a mandibular advancement distance of 50-60% combined with a vertical opening distance of 4-5mm may fall within a low-stress parameter range. With this configuration, loads on the TMJ disc and PDL were reduced by 48.4% and 37.6%, respectively, compared to a 70% advancement distance.

FEA suggested that a mandibular advancement distance of 50-60% of maximum protrusion combined with a vertical opening distance of 4-5mm may represent a biomechanically favourable window within this preliminary single-model analysis. These results should not be interpreted as definitive clinical guidance.