Influence of host periosteum and recipient bed perforation on the healing of onlay mandibular bone graft: an experimental pilot study in the sheep

Purpose The aim of this study was to evaluate the role of host periosteum and recipient bed perforation on the healing of an onlay graft to the mandible based on histologic and immunohistochemical analysis. Materials and methods Each of the 12 adult sheep used in the study received four iliac corticocancellous onlay bone grafts on the lateral surface of the mandible. In experiment 1, the block graft was placed in direct contact with the recipient bed and fixed with micro-screws, and in experiment 2, the recipient cortical bed was perforated before graft placement. The host periosteum around the graft was excised before flap replacement in experiment 3, and in experiment 4, a sheet of silicone membrane was placed between the graft and the recipient bed. The animals were euthanised at 4, 8, 12 and 16 weeks after surgery and the findings were analysed by routine microscopy (haematoxylin and eosin and tartrate-resistant acid phosphatase [TRAP] stains) and immunohistochemistry for proliferation and apoptotic markers (Ki67, caspase-3 and TUNEL stains). Results After 8 weeks, full graft-host integration was seen in all the experimental groups except experiment 4. After 16 weeks, pronounced graft resorption and volume reduction was observed in experiments 1 and 2, whilst experiment 3 was characterised with extensive connective tissue infiltration and severe resorption of the graft. The number of osteoclasts expressed peaked at 4 weeks in experiments 1 and 2 and at 16 weeks in experiment 3. Immunoreactivity for Ki67 by osteoblasts lining the trabecular bone of the graft's spongiosa expressed moderate level of Ki67 at 8 weeks, and thereafter declined markedly. The strongest expression of caspase-3 on the bone surface was observed after 16 weeks. Discussion and conclusion Recipient cortical bed perforation offered no advantage over non-perforated bed regarding healing and integration of a bone graft. Excision of the host overlying the periosteum was accompanied with rapid absorption of the grafts and partial or complete replacement with fibrous connective tissue. This study also demonstrated that cell death by apoptosis is a fundamental component of osteoblastic phenotypic differentiation during healing of corticocancellous bone graft.