Bone-to-Implant Contact and New Bone Formation Within Human Freeze-Dried Bone Blocks Grafted Over Rabbit Calvaria

Purpose: To assess the extent of osseointegration with rough-surface implants and new bone formation (NBF) within human freeze-dried bone blocks (h-FDB) grafted over rabbit calvaria. Materials and Methods: A total of 18 rectangular h-FDB blocks were stabilized bilaterally to the calvaria of nine New Zealand rabbits by two mini titanium screws each. A total of 18 rough-surface implants (5.0 × 6.0-mm) were placed, 9 simultaneously (immediate placement [IP]) on one side and 9 at 3 months after block grafting (delayed placement [DP]) on the contralateral side. At 12 weeks after the second surgical procedure, block biopsies were harvested and processed for histologic analysis. Morphometric measurements consisted of bone-to-implant contact (BIC) and the extent of NBF from the calvarial surface and outward into the block. A paired t test was applied for statistical analysis. Results: All h-FDB blocks were integrated, and the implants showed clinical stability. Histologically, the BIC was primarily between the apical end of the implants and the host rabbit calvaria. Bone growth between the implant threads was minimal and inconsistent among all animals. Morphometric measurements showed that the mean BIC of the IP and DP implants with the blocks was 10.50% ± 5.99% and 23.06% ± 9.58%, respectively (P .001). NBF was observed primarily in the cancellous compartment of the block adjacent to the recipient calvarial bed. The extent of NBF into the block around the IP and DP implants was 9.95% ± 8.41% and 12.90% ± 11.07%, respectively (P = 0.2). Conclusion: In this model, a significantly lower BIC was demonstrated when implants were placed simultaneously with h-FDB block grafting compared to those placed in a two-stage mode. However, both techniques showed limited osseointegration. Keywords: bone-implant contact, FDB bone blocks, freeze-dried bone, graft vascularization, new bone formation, osseointegration