Responses in the Underlying Bone During Migration of Hydroxyapatite Grafts in the Growing Rabbit

Summary

To clarify whether local bone turnover underneath hydroxyapatite grafts differs in nasal and mandibular bones, a single porous hydroxyapatite block was implanted on the respective surface of the right nasal bone and the mandibular ramus in 40 rabbits at the age of 4 weeks. The undecalcified sections of the bone specimens underneath the graft were histomorpho-metrically measured under a light microscope. In all grafted specimens, the hydroxyapatite graft was united, but sinking of the grafts proceeded during 16 weeks. In the nasal bone, bone area density beneath the graft was significantly decreased within 3 weeks and continued to be diminished thereafter. In the mandibular ramus, however, bone area density was maintained at a similar level to that of the sham-operated side. In the nasal bone, the parameters of mineralizing surface and bone formation rates obtained by fluorescence labels were significantly reduced. In the mandibular bone, however, these parameters of bone formation were significantly increased. Mineral apposition rates were reduced in either bone. The parameters of osteoclasts obtained by tartrate-resistant acid phosphatase (TRAP) staining were significantly increased in both the nasal and mandibular bones. These data clearly demonstrated that bone density and local turnover underneath the osteoblast recruitment in the face of increased bone resorption by the grafts depend on the intrinsic factors of individual bones. Osteoblast functions at a cellular level, however, appeared to be commonly disturbed in the neighboring bone of the hydroxyapatite grafts.