When the sinus membrane is removed, the osteoid like layer is encountered and a layer of soft connective tissue is found. Adjacent to the layer of soft connective tissue is hard mineralized bone. This structure may explain why sinus grafting is a very successful procedure. The sinus membrane is perfused with capillaries that penetrate the osteoid-like layer and anastomose with capillaries in the soft connective tissue layer immediately under the osteoid-like layer. The fragility of the osteoid-like layer and the presence of a large soft connective tissue layer immediately beneath the osteoid-like layer provides an excellent source of vascularity and cells of osteogenic potential surrounding the graft site when the remaining alveolar ridge is 2.5 mm in thickness or greater.
When there is greater than 2 mm of alveolar ridge remaining, trabecular bone with its accompanying regenerative cells is found without cortical bone lining the sinus or the alveolar crest. However, when there is less than 2mm of alveolar ridge remaining, trabecular bone is lost and only cortical bone remains. In these cases, the osteoid-like layer is present but it is not backed by a rich layer of soft connective tissue. This is a significant factor in tissue engineering. Cortical bone is over 90% mineralized tissue and contains no regenerative cells. Whereas trabecular bone is less than 50% mineralized tissue and contains regenerative bone precursor cells.
The presence or absence of regenerative cells in the local tissues dictates the tissue engineering principals that need to be considered in order to achieve clinical success. The surgical procedure outlined here is designed for those patients who have approximately 2.5 mm of alveolar ridge remaining or more. Modification of this surgical technique for alveolar ridges with 2 mm or less of bone thickness will be described in a subsequent publication.