Tissue segregation enhances calvarial osteogenesis in adult primates

Calvarial defects of adult mammals have a limited potential for regeneration. Osteogenesis may be impaired by the intrusion within the defect of nonosteogenic tissues during healing, which inhibits centripetal bone deposition from the margins of the defects. Using a primate model, we evaluated bone regeneration in calvarial defects treated with demineralized bone matrix versus defects treated according to the strategy of guided tissue regeneration. Sixty-four defects, 25 mm in diameter, were prepared in 16 adult male baboons (Papio ursinus). In each animal, 2 contralateral defects were covered with a template of porous polymer, 35 mm in diameter. Templates were positioned over the calvarial margins to prevent penetration of the pericranium and the temporalis muscle within the defects, thus maintaining tissue segregation during healing. The third defect was implanted with allogeneic demineralized bone matrix, as positive control. The fourth defect was left untreated and was used as negative control. Undecalcified bone sections (7 microns thick) were prepared from the harvested specimens 3 and 6 months after surgery. Although untreated defects showed limited osteogenesis after fusion of the pericranium with the dura, defects covered with the polymeric template often showed extensive bone deposition extending centripetally from the margins of the craniotomies. Histomorphometry demonstrated that defects treated with demineralized bone matrix and defects covered with the polymeric template had greater amounts of bone and osteoid when compared with untreated defects (p < 0.01). At 6 months, greater amounts of bone formed in demineralized bone matrix-treated defects when compared with defects covered with the polymeric template (p < 0.01). The results of this study show that calvarial membranous bones of adult primates retain the potential to regenerate when segregation between the different tissue components participating in the healing of the wound is maintained. In the same model, however, implantation of allogeneic demineralized bone matrix, used as a positive control provided the most effective treatment for the defects.