When grafting bone over cortical bone, like in vertical augmentation, we decorticate the bone to provide blood supply. When grafting bone in the maxillary sinus we place the graft right over cortical bone. In either case the graft is covered by either sinus membrane or gingiva that provide some blood supply. Is anyone familiar with the biological concept that makes sinus grafts successful? Many possibilities come to mind but speculations are not the answer. Any thoughts?