title: A comparison of synovial fluid pressure after immediate versus gradual mandibular advancement in the miniature pig.
abstract: OBJECTIVE
  Mandibular advancement is a commonly performed surgical procedure for the treatment of mandibular hypoplasia. With the increased use of rigid fixation, there has been a decrease in the amount of relapse but an increase in the amount of force transmitted to the condyles. Gradual advancement of the mandible by distraction osteogenesis slowly overcomes the soft-tissue envelope and may decrease the amount of force exerted on the condyles. The purpose of this study was to develop an animal model to measure the magnitude of pressure associated with immediate versus gradual mandibular advancement.
  
  
  METHODS
  A 2.0-mm pressure transducer was placed in the superior joint space in 2 miniature pigs. In the first animal, immediate advancement of the mandible with rigid fixation was performed. The synovial fluid hydrostatic pressures were measured prior to surgery and postoperatively. A second animal underwent gradual advancement with distraction osteogenesis. The synovial fluid hydrostatic pressures were measured prior to and after each activation of the distraction device. The condyles were examined radiographically and microscopically.
  
  
  RESULTS
  The superior joint space fluid pressures increased and remained elevated over a 5-week period after immediate advancement. In the gradually advanced mandible, the pressures were elevated but returned to near baseline prior to the activation the following day.
  
  
  CONCLUSIONS
  This animal model is useful to directly measure the pressure that is exerted on the condyle. This will allow further studies to compare methods for mandibular advancement. It is likely that gradual advancement of the mandible by distraction osteogenesis produces less force and causes less condylar resorption than large mandibular advancement stabilized with rigid fixation.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Loma Linda University, CA 92350, USA. aherford@sd.llu.edu
authors.forename: Alan S
authors.initials: AS
authors.lastname: Herford
authors.forename: Robert
authors.initials: R
authors.lastname: Hoffman
authors.forename: Samuel
authors.initials: S
authors.lastname: Demirdji
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Boyne
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Caruso
authors.forename: V Leroy
authors.initials: VL
authors.lastname: Leggitt
authors.forename: Luis
authors.initials: L
authors.lastname: Vega
mesh_terms: D000818:Animals; D001860:Bone Plates; D003799:Dental Stress Analysis; D006874:Hydrostatic Pressure; D008297:Male; D019186:Mandibular Advancement / Q000295:instrumentation / Q000379:methods*; D008335:Mandibular Condyle / Q000000981:diagnostic imaging / Q000473:pathology*; D023421:Models, Animal; D019857:Osteogenesis, Distraction; D011859:Radiography; D013552:Swine; D013556:Swine, Miniature; D013582:Synovial Fluid / Q000502:physiology*; D013704:Temporomandibular Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D014160:Transducers, Pressure