title: A mathematical analysis of the role of friction in occlusal trauma.
abstract: BACKGROUND
  It is recognized that high or misdirected forces can cause occlusal trauma. It is also known that the coefficient of friction between contacting teeth depends on (salivary) lubrication and on the material surfaces in contact. Friction changes the directions and magnitudes of contact forces, but the exact influence of friction on occlusal trauma is unknown.
  
  
  OBJECTIVE
  The purpose of this mathematical study was to ascertain the influence of changed friction (as a result of xerostomia or a restoration) on the forces experienced by contacting teeth and the temporomandibular joint (TMJ).
  
  
  METHODS
  Equations were derived for the forces on teeth and the TMJ. To assess the effects of friction on these forces, a parametric analysis was performed in which the coefficient of friction between teeth was set to 0.0 (idealized frictionless contact), 0.2 (salivary lubrication), 0.4 (xerostomia), or 1.0 (some artificial saliva lubrication).
  
  
  RESULTS
  The computations indicated that a change in friction influences the directions and magnitudes of the forces experienced by teeth and the TMJ. The effect can be subtle or profound depending on the cusp angle and the direction of impending motion.
  
  
  CONCLUSIONS
  Within the limitations of this study, the results suggest that change in friction between teeth, for any reason, should be considered a possible cause of occlusal trauma.
authors.affiliation: Department of Oral Facial Development, School of Dentistry, Indiana University, Indianapolis 46202, USA. tkatona@iupui.edu
authors.forename: T R
authors.initials: TR
authors.lastname: Katona
mesh_terms: D003723:Dental Amalgam / Q000009:adverse effects; D003769:Dental Occlusion, Traumatic / Q000209:etiology*; D003776:Dental Porcelain / Q000009:adverse effects; D003793:Dental Restoration, Permanent / Q000009:adverse effects; D003799:Dental Stress Analysis; D017276:Friction; D006801:Humans; D008410:Masticatory Muscles / Q000503:physiopathology; D008954:Models, Biological; D012463:Saliva / Q000502:physiology; D012464:Saliva, Artificial / Q000009:adverse effects; D013499:Surface Properties; D013704:Temporomandibular Joint / Q000503:physiopathology; D014987:Xerostomia / Q000150:complications
chemical_list: D012464:Saliva, Artificial; D003776:Dental Porcelain; D003723:Dental Amalgam