OSTEOBLAST REACTION AT THE INTERFACE BETWEEN SURFACE-ACTIVE MATERIALSAND BONE IN-VIVO - A STUDY USING IN-SITU HYBRIDIZATION

Osteoblast activation after implantation of two kinds of surface-activ e material in bone was investigated chronologically using in situ hybr idization with digoxygenin-labeled procollagen alpha 1(I) complementar y RNA probe. The bioactive materials used were hydroxyapatite (HA) and apatite-and wollastonite-containing glass-ceramic (A-W GC). A hole wa s drilled bilaterally in the distal epiphysis of rabbit femurs with su bsequent implantation of HA or A-W GC cylinders in a press-fit manner. Specimens were collected at 3, 7, 14, and 28 days after operation and decalcified. Then the undecalcified implant cores were pushed out of the hole without causing damage to the bony side of the interface. In situ hybridization documented no qualitative differences in the expres sion of procollagen alpha 1(I) RNA between KA and A-W GC. Few osteobla sts at the bone-material interface showed a specific signal at day 3, whereas many osteoblasts were positive around the materials at days 7 and 14, indicative of active new bone formation. The positive osteobla sts seemed to originate from preexisting trabeculae and lined the trab eculae, newly formed bone, and material surface. At day 28, many osteo blasts lining material surrounding bone were negative, whereas those i n remodeling canals were positive, suggesting that the bone was in the remodeling stage after bone formation. These findings were comparable to those with beta-tricalcium phosphate in a previous study, thus sug gesting osteoconductive bone formation on HA and A-W GC. (C) 1998 John Wiley & Sons, Inc.