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Endogenous up regulation of Bone Morphogenetic Protein 2 (BMP2) in response to recombinant human BMP2 application is segmental mandibular defects. The key of successful bone regeneration

The ability of rhBMP2/ACS to regenerate bone in immediate versus delayed reconstruction of mandibular segmental defect has not been tested. We hypothesized that immediate reconstruction will yield better bone regeneration due to better soft tissue response. A 35 mm mandibular segmental defect was created with periosteal excision in 16 dogs divided in 3 groups. In group1 (n=6) ACS was loaded with 8ml of rhBMP2. In group 2 (n=5) the same dose of rhBMP2/ACS was delivered into the defect 4 weeks after surgery. In group 3 (control; n=5) the defect was reconstructed using ACS loaded with 8ml of buffer only. Tissues were collected after 12 weeks of reconstruction in all groups. Bone histomorphometry was done to evaluate bone regeneration. mRNA expression of both BMP2 and VEGF in the soft tissue surrounding the defect was evaluated using qPCR. The source of endogenous BMP2 was confirmed using immunofluorescence of both BMP2 and CD31. Immediate delivery yielded better bone regeneration. Both BMP2 and VEGF expression were up‐regulated only in group 1 (+7.3; p= 0.001, +1.53; p= 0.001). Immuno‐colocalization of BMP2 and CD31suggested that endothelial cells could be the source of endogenous BMP2. Immediate delivery of rhBMP2 seemed to induce endogenous release of BMP2 from the surrounding soft tissues, an effect that was lacking in delayed delivery and may explain the difference in bone regeneration between the two conditions.