A. Yanagisawa et al., MIGRATION OF HYDROXYAPATITE ONLAYS INTO THE MANDIBLE AND NASAL BONE AND LOCAL BONE TURNOVER IN GROWING RABBITS, Plastic and reconstructive surgery, 99(7), 1997, pp. 1972-1982
To determine the effects of local bone turnover on the migration of ma
croporous hydroxyapatite onlays in the nasal bone and mandibular ramus
, we performed histomorphometric analyses of the underlying bone area
in 41 New Zealand White rabbits from the age of 4 weeks. The hydroxyap
atite implants were placed under the periosteum of the right nasal bon
e (a depository bone onto its periosteal surface and endosteal resorpt
ive) and the mandibular ramus (resorptive onto its outer surface). The
corresponding left sides were sham operated. Following fluorescence b
one labeling, composite specimens of the hydroxyapatite block includin
g both sides of the nasal bone and mandible were removed at 0 (n = 1),
3, 6, 9, 12, and 16 weeks postoperatively (n = 8, respectively) and p
rocessed to yield undecalcified sections. Bone-bone marrow interfaces
in the entire area within 200 mu m beneath the base of the hydroxyapat
ite and in the counter-area on the sham-operated side were measured un
der a light microscope. In all grafted specimens, the hydroxyapatite m
atrix was directly united with the underlying tissue by bone ingrowth.
However, the sinking of the hy droxyapatite graft in the nasal bone w
as significant at 3 weeks postoperatively and gradually increased ther
eafter. In the mandible, the sinking became significant at 6 weeks. In
the nasal bone, the bone area density beneath the graft showed a time
-dependent decrease during the experimental period, but in the mandibu
lar bone, the value was initially decreased at 3 weeks and then recove
red to baseline level. In both bones, parameters of bone resorption, s
uch as osteoclast number and osteoclast surface, were significantly in
creased from 3 weeks. While the parameters of bone formation, such as
osteoblast surface and mineralizing surface, were significantly decrea
sed from 3 weeks in the nasal bone, they were significantly increased
in the mandible. Mineral apposition rate showed a significant decrease
in both bones. Our data indicate that while the bone area density ben
eath the hydroxyapatite seemed to depend on bone formation, increased
bone resorption would be more critical for the remodeling of underlyin
g bony architecture in the migration of the hydroxyapatite graft.