title: Mechanical response of the porcine temporomandibular joint disc to an impact event and repeated tensile loading.
abstract: OBJECTIVE
  To test for orthotropy in the stress-strain behavior of the temporomandibular joint (TMJ) disc under repeated physiologic loading before and after an impact event.
  
  
  METHODS
  Two groups, each consisting of 10 discs, were subjected to repeated tensile cycling in the dorsoventral (group 1) and mediolateral (group 3) direction. Two additional groups, each consisting of 10 discs, had preconditioning in the form of a 1.18 N.s impulsive load before tensile cycling in either the dorsoventral (group 2) or mediolateral (group 4) direction. Physiologic loads of 1 to 3 N were cycled at 0.1 Hz, and stress-strain responses were recorded every cycle between 1 to 10 cycles, and then periodically at 50, 100, 500, 750, and 1,000 cycles. The properties of elastic modulus, residual strain upon unloading, and area contained within the hysteresis loop were measured.
  
  
  RESULTS
  Dorsoventral loading produced 5-fold higher elastic modulus, 5-fold lower residual strain, and 5-fold lower hysteresis compared to mediolateral tensile loading (P < or = .001). Repeated loading effectively reduced the viscous response for all discs, as the elastic modulus increased while residual strain and hysteresis decreased. Impulsive loading caused elastic modulus to increase for dorsoventrally cycled discs, whereas hysteresis decreased for mediolaterally cycled discs (P < or = .05).
  
  
  CONCLUSIONS
  The findings suggest that damage from the impact load may have increased the porosity of the extracellular matrix, which ultimately resulted in additional stress transfer to the collagen fibers during loading. Impulsive loads may be an important preconditioning factor in the fatigue failure of the TMJ disc in vivo.
authors.affiliation: Department of Adult Restorative Dentistry, College of Dentistry, 40th and Holdrege, PO Box 830740, Lincoln, Nebraska 68583-0750, USA. mbeatty@unmc.edu
authors.forename: Mark W
authors.initials: MW
authors.lastname: Beatty
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Nickel
authors.forename: Laura R
authors.initials: LR
authors.lastname: Iwasaki
authors.forename: Mark
authors.initials: M
authors.lastname: Leiker
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001696:Biomechanical Phenomena; D004548:Elasticity; D016014:Linear Models; D016062:Porosity; D013314:Stress, Mechanical; D013552:Swine; D019224:Temporomandibular Joint Disc / Q000502:physiology*; D013997:Time Factors; D014783:Viscosity; D016474:Weight-Bearing