Investigation of the biomechanical effects of severe anterior disc displacement on the temporomandibular joint and occlusion.

The temporomandibular joint (TMJ) and occlusion, as critical load-bearing components of the stomatognathic system, exhibit complex interdependence. While occlusal abnormalities contribute to internal joint disorders, their reciprocal effects remain poorly understood. This study investigates how severe anterior disc displacement (ADD) alters the stress distribution within the TMJ and the occlusion, aiming to elucidate the TMJ-occlusion relationship and inform clinical diagnosis and treatment strategies. Refined finite element models of the masticatory system of the normal, bilaterally severe ADD, and unilaterally severe ADD groups were developed. Stress distributions were analyzed under maximum voluntary intercuspal clenching (MIC) and maximum voluntary unilateral molar clenching (MUC) with corresponding muscle force intensities. Results showed that under high-intensity clenching, the contact stress on the second molars in the severe ADD groups (48.4-50.3 MPa) exceeded that in the normal group (37.7-38.4 MPa). The condylar contact stress of the severe ADD group was more than 40 times greater than that of the normal group. The ranking of peak stresses on the condyles with unilateral severe ADD under different high-intensity tasks was as follows: MUCI (336.97 MPa) > MUCC (206.54 MPa) > MIC (169.19 MPa). In conclusion, severe ADD under high-intensity clenching induces anterior slippage of discs, resulting in abnormal stress concentrations on the condyles and second molars, particularly during ipsilateral clenching. To mitigate potential biomechanical risks, patients are encouraged to adopt balanced mastication habits.