A 1-year study of hydroxyapatite-derived biomaterials in an adult sheep model: III. Comparison with autogenous bone graft for facial augmentation

Background: The present study investigates onlay bone grafts and implants in a large-animal (sheep) model to determine whether there are composite biomaterials that can maximize long-term facial augmentation when compared with conventional bone grafts. Methods: Facial augmentation was performed in 10 adult sheep. First, 16.8 X 5-mm disks were prepared from autogenous calvarial bone, hydroxyapatite ceramic, ceramic composite of 60 percent hydroxyapatite and 40 percent P-tricalcium phosphate (60 percent hydroxyapatite ceramic), and hydroxyapatite cement paste. Facial recipient sites were the body of the mandible (depository), the maxillary region (resorptive), and the frontal bone (depository). The volume of all bone grafts and implants was determined using computed tomographic scans, and the amount of bone formation was measured by means of backscatter electron microscopy 1 year postimplantation. Results: Cranial bone graft demonstrated a highly significant reduction in volume in all sites studied. Other than a slight decrease in volume of hydroxyapatite cement paste disks applied to the maxillary region, there was no significant change in volume of the biomaterials implanted in any of the remaining recipient sites. Bone replacement was greatest in hydroxyapatite ceramic (23.9 percent) followed by 60 percent hydroxyapatite ceramic (16.4 percent) and least with hydroxyapatite cement paste (4.2 percent). Minimal differences in bone replacement were noted between recipient sites. Conclusions: This study demonstrates that the volume maintenance of onlay hydroxyl apatite composites is highly predictable, whereas that of cranial bone graft is unpredictable. Minimal differences were seen in bone replacement within biomaterials between "depository" and "resorptive" facial recipient sites. Ceramic forms of onlay hydroxyapatite implants demonstrated significantly greater bone replacement than did the cement paste forms of hydroxyapatite.