title: The osteoinductivity of silicate-substituted calcium phosphate.
abstract: BACKGROUND
  The osteoinductivity of silicate-substituted calcium phosphate and stoichiometric calcium phosphate was investigated with use of ectopic implantation. Implants with a macroporosity of 80% and a strut porosity of 30% were inserted into sites located in the left and right paraspinal muscles of six female sheep.
  
  
  METHODS
  After twelve weeks in vivo, a longitudinal thin section was prepared through the center of each implant. Bone formation within the implant, bone formation in contact with the implant surface, and implant resorption were quantified with use of a line intersection method. The specimens were also analyzed with use of backscattered scanning electron microscopy and energy-dispersive x-ray analysis.
  
  
  RESULTS
  Silicate substitution had a significant effect on the formation of bone both within the implant and on the implant surface during the twelve-week period. Bone area within the implant was greater in the silicate-substituted calcium phosphate group (mean, 7.65% ± 3.2%) than in the stoichiometric calcium phosphate group (0.99% ± 0.9%, p = 0.01). The amount of bone formed at the surface of the implant was also significantly greater in the silicate-substituted calcium phosphate group (mean, 26.00% ± 7.8%) than in the stoichiometric calcium phosphate group (2.2% ± 2.0%, p = 0.01). Scanning electron microscopy demonstrated bone formation within pores that were <5 μm in size, and energy-dispersive x-ray analysis confirmed the presence of silicon within the new bone in the silicate-substituted calcium phosphate group.
  
  
  CONCLUSIONS
  The formation of bone within muscle during the twelve-week period showed both silicate-substituted calcium phosphate and stoichiometric calcium phosphate to be osteoinductive in an ovine model. Silicate substitution significantly increased the amount of bone that formed and the amount of bone attached to the implant surface. New bone formation occurred through an intramembranous process within the implant structure.
authors.affiliation: John Scales Centre for Biomedical Engineering, Institute of Orthopaedics and Musculoskeletal Science, University College London, United Kingdom. m.coathup@ucl.ac.uk
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Coathup
authors.forename: Sorousheh
authors.initials: S
authors.lastname: Samizadeh
authors.forename: Yvette S
authors.initials: YS
authors.lastname: Fang
authors.forename: Thomas
authors.initials: T
authors.lastname: Buckland
authors.forename: Karin A
authors.initials: KA
authors.lastname: Hing
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Blunn
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000648:ultrastructure; D002130:Calcium Phosphates / Q000494:pharmacology*; D005260:Female; D008855:Microscopy, Electron, Scanning; D010012:Osteogenesis / Q000187:drug effects*; D016062:Porosity; D019736:Prostheses and Implants; D012756:Sheep; D017640:Silicates / Q000494:pharmacology*
chemical_list: D002130:Calcium Phosphates; D017640:Silicates; C020243:calcium phosphate