title: The process of lubrication impairment and its involvement in temporomandibular joint disc displacement: a theoretical concept.
abstract: OBJECTIVE
  This article re-evaluates the chain of events leading to temporomandibular joint (TMJ) disc displacement. The joint lubrication system and the process of its breakdown are clarified and an attempt is made to evaluate the possible effect of increased friction between the disc and fossa on the anterior displacement of the disc.
  
  
  METHODS
  The study is based on the author's accumulated clinical data and results obtained from laboratory investigations regarding TMJ lubrication and its possible breakdown, coupled with pertinent information culled from the literature.
  
  
  RESULTS
  Translation of the disc in the TMJ is enabled due to the presence of phospholipids and hyaluronic acid, which constitute an efficient lubrication system. This system may break down in the presence of uncontrolled free radicals. In the absence of lubricants, the articular surfaces are smooth, elastic in texture, and possess strong surface energy. Such opposing planes, especially in the presence of a thin fluid film (sub-boundary lubrication) tend to generate high friction while the disc is sliding against the fossa. Such friction is probably the prime mover in loosening the disc attachments to the condyle, with subsequent disc displacement.
  
  
  CONCLUSIONS
  Increased friction of the contiguous parts may well be a major causative factor in displacement of the articular disc. This should be taken into account in considering the appropriate treatment approach. It also raises some doubts regarding the validity of using repositioning techniques.
authors.affiliation: The Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel. Dorrit@cc.huji.ac.il
authors.forename: D W
authors.initials: DW
authors.lastname: Nitzan
mesh_terms: D004548:Elasticity; D005609:Free Radicals; D017276:Friction; D006801:Humans; D006820:Hyaluronic Acid / Q000502:physiology; D004204:Joint Dislocations / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy; D008153:Lubrication; D008335:Mandibular Condyle / Q000503:physiopathology; D010743:Phospholipids / Q000502:physiology; D013500:Surface Tension; D013582:Synovial Fluid / Q000502:physiology*; D013701:Temporal Bone / Q000503:physiopathology; D019224:Temporomandibular Joint Disc / Q000503:physiopathology*
chemical_list: D005609:Free Radicals; D010743:Phospholipids; D006820:Hyaluronic Acid