title: A 5-year in vitro and in vivo study of the biodegradation of polylactide plates.
abstract: OBJECTIVE
  The purpose of this study was to investigate the long-term tissue response and duration of degradation of self-reinforced poly-L-lactide (SR-PLLA) multilayer plates in vivo.
  
  
  METHODS
  Mandibular osteotomies in sheep were fixed with SR-PLLA multilayer plates. The animals were followed for 1, 2, 3, 4, and 5 years, after which histologic studies were performed.
  
  
  RESULTS
  The foreign-body reaction was mainly mild, and the osteotomies were well united. After 5 years in vivo, the material was almost completely resorbed, but small particles of polymer could still be detected at the implantation site. SR-PLLA plates were also incubated in vitro for 5 years. The material degraded considerably faster in vivo than in vitro. Molecular weight, melting temperature, and crystallinity of the plates remained at a constant level after 2 years in vitro, indicating very slow degradation of the oligomeric (molecular weight [Mw], 3500 daltons), highly crystalline (heat of fusion, 70 J/g), PLLA residue solely as a result of hydrolysis. Although the plates became increasingly fragile as they degraded, they retained their macroscopic form until the end of the 5-year follow-up. Loss of mass of the plates was 52%+/-8% after 5 years of incubation in vitro.
  
  
  CONCLUSIONS
  Although the long degradation period may seem to be a minor drawback to the use of such plates, it does not appear to affect the healing process.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Helsinki University Central Hospital, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Suuronen
authors.forename: T
authors.initials: T
authors.lastname: Pohjonen
authors.forename: J
authors.initials: J
authors.lastname: Hietanen
authors.forename: C
authors.initials: C
authors.lastname: Lindqvist
mesh_terms: D000042:Absorption; D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry / Q000493:pharmacokinetics*; D001673:Biodegradation, Environmental; D001860:Bone Plates; D001863:Bone Screws; D002152:Calorimetry, Differential Scanning / Q000379:methods; D005069:Evaluation Studies as Topic; D066298:In Vitro Techniques; D008334:Mandible / Q000601:surgery; D008970:Molecular Weight; D010027:Osteotomy; D011091:Polyesters / Q000737:chemistry / Q000493:pharmacokinetics*; D012756:Sheep; D013718:Tensile Strength; D013997:Time Factors; D014783:Viscosity
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C033616:poly(lactide)