A Study On The Stress Distribution In The Temporomandibular Joint Affected By Tooth Wear With Three-Dimensional Finite Element Method

Objective:Tooh wear is the loss of tooth hard tissue without the causes such as tooth caries, acute injury and developmental factors, which can lead to bad influence on tooth hard tissue, periodontal tissue, temporomandibular joints , etc . The excessive tooth wear can result in the decrease of occlusional vertical distance and the change of occlusion relationship, which gives rise to the change of temporomandibular joints even temporonandibular disorders.In order to identify the mechanism of temporomandibular disorders which is caused by excessive tooth wear, this study adopt the three-dimensional finite element method of temporomandibular joints and simulate the tooth wear of 1/3, 1/2, 2/3 and total height respectively on computer. Then we analyze the stress distribution of temporomandibular joint in intercupided occlusion, thus we can find out the biological force change of temporomandibular joint after tooth wear. Methods:At first, we select a male and healthy volunteer who has integral dentition, normal occlusion relationship, posterior tooth with neutroclusion and has not any symptoms, signs and history of temporomandibular disorders. Then we use SOMATOM Banlance spiral CT to scan the people on coronary site which should include temporomandibulor joints with articular disc, articular cartilage, spongy bone, compact bone and masticatory muscles, mandible and the lower tooth. The acquired images in turn are processed by Scan Maker, Photoshop 7.0, Auto-CAD 2004 and Unigraphics. The figures obtained are infused in three-dimensional finite element software-MSC.Marc in which the model can beautomatically web separated. Then we simulate the tooth wear of 1/3,1/2,2/3 and total height respectively accompanyed the decrease of occlusional vertical distance . At last, we analyze the stress distribution of the temporomandibular joint in intercupided occlusion . Results:With the increasing tooth wear, the stress of condyle surface is increasing too . When the tooth are totally worn, the Von Mises is four times that of the normal. The site with maximum Von Mises does not change and is still located in the lateral area of condyle anterior inclined plane. With the increasing tooth wear, the Von Mises stress of articular disc is also increasing and its increasing speed is faster than that of condyle and glenoid fossa . There is stress concentration on the posterior edge of posterior band of articular disc , the middle and lateral area of intermediate zone and posterior band of the disc . The deformation of articular disc is aggravating and articular disc becomes thinner with the increasing tooth wear . At the same time , the stress of glenoid fossa is also increasing , the site with maximum stress changes from the posterior inclined plane of the articular eminence to the roof of the glenoid fossa. Conclusions:In our study , the conclusions are : â‘ with the increasing tooth wear , the stress of condyle is increasing . There are stress concentration in the anterior inclined plane and lateral area of condyle . The deformation of condyle is also increasing ; â‘¡with the decrease of occlusion vertical distance , the stress and deformation of articular disc increase apparently , which is more serious than that of condyle . The stress change of articuar disc may be the main cause of temporomandibular disorders ; â‘¢with the increasing tooth wear, the increase of Von Mises stress of glenoid fossa is not apparent. But the stress of posterior inclined plane of articular eminence is increasing apparently ; â‘£the tooth wear can lead to the increase of stress in temporomandibular joint and stress concentration .If the increasing stress exceeds the adapatability and adjustability of condyle and articular disc , it can injure the tissue of joint, which may cause temporomandibular disorders .