Three-dimensional finite element analysis of temporomandibular joint stresses following botulinum toxin injection and occlusal splint therapy in bruxism

BACKGROUND: Bruxism-related clenching can impose excessive mechanical loads on the temporomandibular joint (TMJ), particularly in the presence of anterior disc displacement (ADD). Understanding how different therapeutic strategies influence joint stress under these conditions can support exploratory, hypothesis-generating assessment of biomechanical unloading within patient-specific models. Therefore, this study aimed to evaluate TMJ stress distributions under normal and displaced disc conditions and to assess the biomechanical effects of simulated treatment strategies using a patient-specific finite element framework. MATERIALS AND METHODS: A patient-specific three-dimensional finite element model derived from clinically acquired computed tomography (CT) data was constructed to simulate TMJ biomechanics during clenching. Stress patterns were analyzed under three disc conditions: normal disc position, unilateral ADD, and bilateral ADD. Intervention scenarios included simulated reductions in masticatory muscle forces representing botulinum toxin Type-A (BoNT-A) therapy and occlusal splint therapy, applied individually and in combination. Peak von Mises stresses within the articular disc and joint structures were compared across all conditions. RESULTS: ADD increased peak stresses within the articular disc and adjacent joint surfaces and shifted stress concentration toward the posterior region of the disc. Simulated reductions in muscle force resulted in progressive decreases in peak joint stresses as additional muscle groups were targeted, whereas splint therapy alone provided moderate stress reduction. The greatest biomechanical unloading was observed when occlusal splint therapy was combined with BoNT-A-related muscle force reduction. Notably, a strategy targeting the masseter and temporalis muscles combined with splint therapy produced lower peak disc stresses than a three-muscle reduction strategy without splint across all disc conditions. CONCLUSION: In this exploratory single-patient finite element model, ADD increased predicted TMJ stresses during clenching, whereas simulated muscle-force reduction and splint-related changes in occlusal load transmission reduced peak stress metrics, with the largest reductions observed in combined scenarios. These results are hypothesis-generating and intended for relative, within-model comparisons under stated assumptions rather than clinical treatment recommendations.