Resorption Pattern and Bone Regeneration Using a Synthetic Bone Substitute Block With or Without rhBMP-2 and Bisphosphonates: An in Vivo Experiment

Abstract

This study aimed to investigate whether recombinant human bone morphogenetic protein-2 (rhBMP-2) or bisphosphonate added to synthetic block bone substitute influences new bone formation and grafting material degradation patterns. In a rabbit calvarial model, four critical-size bone defects were created and treated with a saline-soaked synthetic bone block (SBB group), bisphosphonate-soaked synthetic bone block (BPS group), rhBMP-2-soaked synthetic bone block (BMP group), or left untreated as control (control group). At 8 weeks, synchrotron-based micro-computed tomography (micro-CT) and histological analyses were performed. All outcomes were evaluated separately in intrabony areas, embedded within the native bone, and extrabony areas, extending beyond the bone surface. Synchrotron-based micro-CT analysis revealed limited resorption of the synthetic bone block across all groups, as the mean percentages of synthetic bone block resorption of the SBB group, BPS group, and BMP group were 8.56%, 11.13%, and 9.11%, respectively, with no significant differences. The cylindric morphology of the grafts was preserved even in the exophytic extrabony portion. Histological evaluation showed that BMP significantly enhanced new bone formation, particularly in the intrabony area (2.65 mm2 for SBB group, 1.37 mm2 for BPS group, and 4.41 mm2 for BMP group in mean). Despite these differences in osteogenic activity, neither bisphosphonate nor rhBMP-2 markedly increased graft resorption, as residual bone graft material was well preserved. Synthetic bone blocks could provide volume stability in both intrabony and extrabony regions, regardless of the addition of bioactive mediators. RhBMP-2 enhanced bone regeneration, though.