Finite Elements Analysis Of Stabilization Occlusal Splint Therapy On Unilateral Temporomandibular Joint Anterior Disc Displacement

Objective: This study aimed to investigate the effect of occlusal splint thickness on stress distribution in the TMJ with unilateral disc anterior displacement without reduction,and to determine the most optimal thickness.Materials and methods: A 26-year-old healthy subject was selected in this study,CBCT and MRI data were acquired.A three-dimensional finite element model of temporomandibular joint with unilateral disc anterior displacement without reduction was reconstructed as the basic model(0mm),and then the models with various thickness of occlusal splint(2mm,3mm,4mm,5mm,6mm)were established based on TMJ CT using Mimics,Geomagic Studio,NX and Ansys software.On all models,the overall stress distribution of bilateral temporomandibular joint and the initial displacement of bilateral disc were evaluated.The disc was divided into five regions: anterior zone,intermediate zone,posterior zone,medial zone and lateral zone,and the regional stress distribution of disc also was measured.Results: The three-dimensional finite element model of temporomandibular joint with left unilateral anterior disc displacement without reduction,and that with occlusal splint of various thickness were successfully established.Overall stress distribution of the temporomandibular joint: in the basic model,the stress of the right disc was the largest,and that of the temporal fossa cartilage was the lowest,while that of the left condylar cartilage was the largest,and that of the temporal fossa cartilage was the lowest,and the maximum von Mises stress of the bilaminar region was close to that of the disc.With the increase of the thickness of stabilization occlusal splint,the stress of bilateral condylar cartilage and articular fossa cartilage fluctuated.In the 5mm and 6mm model,the maximum von Mises stress of right articular fossa cartilage was higher than that of condylar cartilage.The maximum principal stress of bilateral disc increased gradually,and the maximum principal stress on the left side was smaller than that on the right side.Stress distribution of disc and bilaminar region: in the basic model,the stress of the left disc was mainly distributed on the posterior zone,and that of the right disc was mainly distributed on the lateral side of the intermediate zone.With the increase of the thickness of the stabilization occlusal splint,the maximum von Mise stress of the left disc and bilaminar region increased gradually,and that in the 2mm model was lower than that in the basic model,while the maximum von Mises stress of the right disc increased gradually,and that in the basic model was the lowest.The maximum von Mises stress in the right bilaminar region fluctuated,and that in the 2mm,4mm and 5mm models was lower than that in the basic model.In all models,the maximum von Mises stress in the left bilaminar region was larger than that in the right side.Regional stress distribution of disc: with the increase of the thickness of stabilization occlusal splint,the maximum von Mises stress of the intermediate zone of right disc gradually increased,and the stress in the3 mm,4mm,5mm and 6mm models increased significantly,the maximum von Mises stress of the lateral zone of right disc fluctuated and changed insignificantly,the maximum von Mises stress of the posterior zone of left disc increased gradually,and the stress in the 3mm,4mm,5mm and 6mm models increased significantly.Displacement trend of TMJ disc: the displacement vector of disc was obtained from the model,the displacement vector of left disc was anterior-medial direction,and the right was medial direction.With the increase of the thickness of the stabilization occlusal splint,the initial displacement of the left disc gradually increased,while that of the right disc decreased at first and then increased,the initial displacement of the 2mm,3mm,4mm and 5mm models was lower than that of the basic model,and that of the 3mm model was the lowest.Conclusion: Stabilization occlusal splint can improve the biomechanical conditions of temporomandibular joint,and 2mm is the optimal thickness for the treatment of unilateral irreducible anterior displacement of articular disc.