De Novo periosteum formation and remodeling activity in human cortical shells versus autograft blocks: stereological quantification of bone cells in rabbit calvarial defect models

This study aimed to characterize periosteal formation and remodeling activity by stereological quantification of osteoblasts, osteoclasts, and osteocytes in autograft blocks and human cortical shells (HCS), providing a histological basis for bone regeneration procedures. Eight male New Zealand white rabbits received paired 5 mm calvarial defects filled with either autograft blocks or mineralized freeze-dried, gamma-irradiated HCSs, after complete periosteum removal to ensure de novo healing. After 12 weeks, the specimens were harvested, and osteoblast, osteoclast, and osteocyte densities were quantified using the optical dissector method. Statistical analyses were performed using paired<i>t</i>-tests. All grafts were well integrated with healthy soft tissues and had no complications. HCSs more frequently contained immature woven bone, whereas autografts predominantly contained mature lamellar bone. Osteoblast and osteoclast densities showed no significant differences between the groups, but the autografts exhibited significantly higher osteocyte density (<i>p</i>= 0.0026). Mineralized freeze-dried, gamma-irradiated HCSs support de novo periosteal regeneration and remodeling activity comparable to that of autograft blocks despite processing-related devitalization. While autografts mature faster, host-driven periosteal repair may offset the graft deficits over time. These findings provide preliminary histological evidence of the clinical potential of allogeneic bone regeneration, warranting further long-term studies.