Histologic results
The bone-to-implant contact ratio within the marrow space of the tibia of the implant group, the hydrogel group, and the BMP-2 group was 8.3 ± 2.1 % (n = 6), 7.6 ± 3.8 % (n = 6), and 23.2 ± 6.4 % (n = 6) respectively. The bone-to-implant contact ratio for the BMP-2 group was significantly higher than the ratios of the implant group and the hydrogel group (P = 0.0003 and 0.0004, respectively).
The undecalcified histology results indicated that the implant group showed stable fixation between the fixture and the cortical bone, but only a small amount of new bone formation around the fixture was observed in the tibia marrow space (Fig. 7). The hydrogel group also showed good osseointegration between the fixture and the cortical bone, but even less new bone formation was evident around the fixture in the tibia marrow space than was seen in the implant group. The intervening fibrous tissue found within the pitch and within the marrow space suggested that the injected composite became fibrous tissue without forming bone. In comparison, the BMP-2 group showed strong ossetointegration in the cortical bone and osseous tissue was connected to the marrow space along the fixture. Newly formed bone was evident around the fixture in the marrow space and remnant hydrogel powder was observed where new bone was formed.
Fig. 7 Undecalcified histology. The image magnification on the left and right was ×12.5 and ×40, respectively. a Only a dental implant fixture was implanted (implant group). Bone coupling with cortical bone was stable, but the osseous tissue associated with the fixture screws in the marrow space was insignificant; b A composite of the β-TCP microspheres and the hyaluronic acid powder gel was injected and a dental implant fixture was inserted (hydrogel group). Bone bonding in the cortical bone was also robust, but new bone formation in the marrow space was insignificant even in comparison to the implant group. The tissue within the pitch is composed of fibrous tissue and exists as intervening tissue between the bony tissues of the marrow space; c A composite of the rhBMP-2 loaded β-TCP microspheres and the hyaluronic acid powder gel was injected and a dental implant fixture was inserted (BMP-2 group). The bone bonding in the cortical bone was stable and osseous tissue was connected from the cortical bone to the marrow space. Newly formed bone was evident around the fixture within the marrow space, and newly formed bone was fused with the fixture