Time-related deviations of fibronectin and type I, II and III collagen on the interface between a hydroxyapatite disc and the rim of a calvarial trephine defect in rabbits

To pursue the events around hydroxyapatite (HA) discs (diameter 9 mm), implanted in calvarial defects in rabbits (diameter 11 mm), immunohistochemical changes of fibronectin and type I, II and III collagen were quantitatively determined in the connective tissue-HA (CTHA) and host bone-HA (BHA) interface at 8, 12 and 16 wk postimplantation. A marked enhancement of type I collagen staining in the BHA interface was noted at the 12th and the 16th wk in comparison to the CTHA interface and connective tissue in the untreated control defect. However, one of the characteristics of the staining in the CTHA interface was the finding of exceptionally high fibronectin and type III collagen at the 8th and the 12th wk in contrast to the BHA interface and the untreated control defect. The change in these immunohistochemically determined compositions was probably due to an active proliferation of vascular components in the CTHA interface. Bone regeneration in the CTHA interface was parallel to an increase in type I collagen and a decrease in fibronectin and type III collagen from 8 to 16 wk. This study indicated that variances in composition or characteristics of connective tissue in CTHA interface have taken place ahead of bone morphogenesis. The time-related derivation of connective tissue matrix components in the BHA and CTHA interface was confined to the interaction of implanted HA with host tissues in contact with the implant.