title: The effect of removal of the disc on the friction in the temporomandibular joint.
abstract: OBJECTIVE
  The amount of friction in the temporomandibular joint (TMJ) is dependent on the joint components, including the synovial fluid, disc, and articular surface cartilage. As friction in the TMJ is less than in other (discless) joints, we hypothesized that this is caused by the presence of the disc.
  
  
  METHODS
  The frictional coefficient of the TMJ was first measured in the intact porcine joint (n = 10). After the disc was removed the measurement of frictional coefficient was conducted again. Furthermore, the subsequent effects of loading duration and the application of hyaluronic acid (HA) were examined.
  
  
  RESULTS
  The mean frictional coefficient in the intact joint was 0.0177 (SD 0.0021). After disc resection it became 0.0361 (SD 0.0063). The frictional coefficient increased with the length of the preceding loading duration and exceeded 0.0635 (SD 0.0085) after 30 minutes. Subsequent application of HA resulted in a slight decrease of the frictional coefficient.
  
  
  CONCLUSIONS
  The presence of the disc reduces the amount of friction in the TMJ. This reduction is likely due to the role of the disc in reducing the amount of incongruity between the articular surfaces and in increasing synovial fluid lubrication.
authors.affiliation: Department of Orthodontics and Craniofacial Developmental Biology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan. etanaka@hiroshima-u.ac.jp
authors.forename: Eiji
authors.initials: E
authors.lastname: Tanaka
authors.forename: Diego A
authors.initials: DA
authors.lastname: Dalla-Bona
authors.forename: Tatsunori
authors.initials: T
authors.lastname: Iwabe
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kawai
authors.forename: Eizo
authors.initials: E
authors.lastname: Yamano
authors.forename: Theo
authors.initials: T
authors.lastname: van Eijden
authors.forename: Masao
authors.initials: M
authors.lastname: Tanaka
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Miyauchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Takata
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tanne
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects / Q000502:physiology; D017276:Friction; D006820:Hyaluronic Acid / Q000494:pharmacology; D008153:Lubrication; D013314:Stress, Mechanical; D013552:Swine; D013582:Synovial Fluid / Q000502:physiology; D013704:Temporomandibular Joint / Q000502:physiology*; D019224:Temporomandibular Joint Disc / Q000502:physiology / Q000601:surgery*
chemical_list: D006820:Hyaluronic Acid