CELL AND MATRIX REACTIONS AT TITANIUM IMPLANTS IN SURGICALLY PREPAREDRAT TIBIAE

The tissue response of rat tibiae to the surgical placement of commerc ially pure titanium implants was examined at 2, 6, 10, and 28 days. Th e transcortical placement of 1.5-mm X 2-mm implants resulted in the ap position of threaded implant surfaces within cortical and cancellous r egions of the tibia. In all regions, evidence of bone formation was ob tained through pre-embedding fracture of the implant from the bane tis sue interface. Scanning electron microscopy examination of early respo nses revealed a fibrin clot and rapid formation of a loosely organized collagenous matrix. Many extravasated blood cells contacted the impla nt surface. At day 6, a more organized matrix containing many blood ve ssels opposed the implant surfaces, and few extravasated blood cells r emained in contact with the implant surface. By day 10, the surgical w ound was filled with woven bone that approximated the contours of the threaded implant. Later, few cells were attached to the retrieved impl ants. The consolidation of the forming matrix was clearly evident at 2 8 days. The tissue interface was an amorphous matrix that revealed the surface characteristics of the machined implant. Light microscopic an alysis of ground sections indicated that, from day 6 onward, cells mor phologically consistent with the osteoblastic phenotype were predomina nt within the gap between the surgical margin and implant surface. Ost eoblastic cells had achieved the formation of an osteoid seam upon whi ch bone formation progressed. The matrix that had formed represented w oven bone containing many osteocytes. At day 6, evidence of remodeling was observed at sites distant from the surgical site, and by day 28 o steoclastic activity was observed at trabecular sites adjacent to the implant surface. The rat tibia model provides evidence of rapid format ion of bone at implant surfaces.