title: Modeling of muscle forces in humans with and without temporomandibular joint disorders.
abstract: OBJECTIVE
  Subjects with/without temporomandibular joint disorders (TMJD) were tested for differences in muscle forces.
  
  
  METHODS
  School of Dental Medicine, University at Buffalo. Ninety-one subjects were classified in four groups based on the presence/absence (±) of chronic myofascial and/or TMJ pain (P) and bilateral disc displacement (DD).
  
  
  METHODS
  Validated numerical models employed an organizational objective and subjects' anatomy to calculate masticatory muscle forces during static biting. anova and Holm's step-down procedure post hoc tests assessed group differences. Theoretical geometries, representing the range of subjects' muscle orientations, were surveyed via numerical models to identify key combinations resulting in high muscle forces. Effect size (Cohen's d) and anova/post hoc tests assessed group differences in key muscle orientations.
  
  
  RESULTS
  +P-DD subjects had significantly higher muscle forces, especially for lateral pterygoid muscles, compared to the other groups (p<0.01) for bite forces that were directed posteromedially or posterolaterally on mandibular molars and posteriorly and slightly medially on mandibular incisors. Key muscle orientations for peak lateral pterygoid muscle forces were identified, and group comparisons showed mean orientation in +P-DD compared to other diagnostic groups was ≥5° more upright for masseter and ≥3° more posteriorly directed for temporalis muscles (all Cohen's d≥0.8).
  
  
  CONCLUSIONS
  Predicted lateral pterygoid muscle forces were significantly higher in +P-DD compared to other groups for specific biting conditions and were attributable, in part, to differences in masseter and temporalis muscle orientations.
authors: Departments of Orthodontics & Dentofacial Orthopedics and Oral & Craniofacial Sciences, University of Missouri-Kansas City, Kansas City, MO, USA.
authors: L R
authors: LR
authors: Iwasaki
authors: H
authors: H
authors: Liu
authors: Y M
authors: YM
authors: Gonzalez
authors: D B
authors: DB
authors: Marx
authors: J C
authors: JC
authors: Nickel
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007180:Incisor / Q000503:physiopathology; D004204:Joint Dislocations / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology; D008410:Masticatory Muscles / Q000503:physiopathology*; D008954:Models, Biological; D008963:Molar / Q000503:physiopathology; D011626:Pterygoid Muscles / Q000503:physiopathology; D013314:Stress, Mechanical; D013703:Temporal Muscle / Q000503:physiopathology; D019224:Temporomandibular Joint Disc / Q000503:physiopathology; D013705:Temporomandibular Joint Disorders / Q000145:classification / Q000503:physiopathology*; D013706:Temporomandibular Joint Dysfunction Syndrome / Q000503:physiopathology; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: biomechanics; computer models; human; masticatory muscles; temporomandibular joint