title: Effect of jaw opening on the stress pattern in a normal human articular disc: finite element analysis based on MRI images.
abstract: BACKGROUND
  Excessive compressive and shear stresses are likely related to condylar resorption and disc perforation. Few studies have reported the disc displacement and deformation during jaw opening. The aim of this study was to analyze stress distribution in a normal articular disc during the jaw opening movement.
  
  
  METHODS
  Bilateral MRI images were obtained from the temporomandibular joint of a healthy subject for the jaw opening displacement from 6 to 24 mm with 1 mm increments. The disc contour for the jaw opening at 6 mm was defined as the reference state, and was used to establish a two dimensional finite element model of the disc. The contours of the disc at other degrees of jaw opening were used as the displacement loading. Hyperelastic material models were applied to the anterior, intermediate and posterior parts of the disc. Stress and strain trajectories were calculated to characterize the stress/strain patterns in the disc.
  
  
  RESULTS
  Both the maximum and minimum principal stresses were negative in the intermediate zone, therefore, the intermediate zone withstood mainly compressive stress. On the contrary, the maximum and minimum principal stresses were most positive in the anterior and posterior zones, which meant that the anterior and posterior bands suffered higher tensile stresses. The different patterns of stress trajectories between the intermediate zone and the anterior and posterior bands might be attributed to the effect of fiber orientation. The compression of the intermediate zone and stretching of the anterior and posterior bands caused high shear deformation in the transition region, especially at the disc surfaces.
  
  
  CONCLUSIONS
  The stress and strain remained at a reasonable level during jaw opening, indicating that the disc experiences no injury during functional opening movements in a healthy temporomandibular joint.
authors.forename: Qihong
authors.initials: Q
authors.lastname: Li
authors.forename: Shuang
authors.initials: S
authors.lastname: Ren
authors.forename: Cheng
authors.initials: C
authors.lastname: Ge
authors.forename: Haiyan
authors.initials: H
authors.lastname: Sun
authors.forename: Hong
authors.initials: H
authors.lastname: Lu
authors.forename: Yinzhong
authors.initials: Y
authors.lastname: Duan
authors.affiliation: Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China. qrong@pku.edu.cn.
authors.forename: Qiguo
authors.initials: Q
authors.lastname: Rong
mesh_terms: D000293:Adolescent; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007568:Jaw / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D013314:Stress, Mechanical; D019224:Temporomandibular Joint Disc / Q000502:physiology*; D013718:Tensile Strength