Maxillary edentulism, together with periodontal disease, is the condition that most frequently induces disruption of alveolar bone tissue. Indeed, the stimulus of the periodontal ligament is lost and the local bone tissue becomes subject to resorption processes that, in the six months following the loss of the tooth, result in alveolar defects or more extensive maxillary atrophy. In both cases, loss of vestibular cortical bone is followed by reduction in the vertical dimension of the alveolar process, producing effects that upset the morphology of the three-dimensional relations between the dental arches. Maintenance, or restoration, of sufficient bone volume to withstand prosthetic loading and the insertion of an endosseous implant, demands the implementation of operating protocols that bring about bone regeneration in the defect sites. Given the biological principles involved, this requires the implementation of osteogenesis, osteoinduction and osteoconduction protocols.
Osteogenesis is the synthesis of new bone by autologous cells that remain viable, given the capacity of the grafted material to become part of the newly forming bone tissue; osteoinduction is based on the capacity of the grafted material to induce the migration, proliferation and phenotypic conversion, into bone-producing cells, of multipotent undifferentiated cells derived from connective tissue or bone marrow; osteoconduction, meanwhile, provides three-dimensional support and guidance to osteoblast precursors within the defect. The operating procedures implemented take into account the size and morphology of the defect, for the restoration of which guided repair or an out-and-out regenerative protocol may be sufficient. Guided repair exploits the principle of resorption/replacement of the biomaterial with newly-formed bone and consists of restoring the lost bone tissue through the implantation of different, osteointegrative biomaterials. This type of repair requires the application of biocompatible osteoconductors which will gradually be absorbed and replaced by newly formed tissue. Instead, the clinical-surgical basis of bone regeneration is: guided bone regeneration (GBR), the use of growth factors and the application of grafts/osteointegrative materials. GBR, through the use of membranes (resorbable or non-resorbable) allows the filling of a defect, “guiding” the growth only of the osteogenic lines and preventing the invasion of non-osteogenic tissues that compete with the bone. This objective is achieved also thanks to the capacity of the membranes to serve as a filter, thereby strengthening the osteocompetent lines and, at the same time, keeping epithelial cells away. The clinical use of GBR, partly on account of its predictable results, is now very widespread. The growth factors used in bone regeneration are glycoproteins which exert autocrine and paracrine effects on the primordial cells in the site. One of these factors, plasma-rich protein (PRP), is an autologous source of growth factors; obtained by separating and concentrating the platelets in a small volume of plasma, it is immediately utilisable in the surgical site. As regards the osteointegrative materials we can distinguish between autologous, homologous, heterologous, and alloplastic grafts. Of these, autologous bone is the gold standard as it has osteogenic, osteoinductive, and osteoconductive properties and, being fresh, keeps osteoblasts viable. Depending on the size of the defect to be treated, harvesting is from endoral or extraoral sites (calvaria, iliac crest, tibia). The harvested material conserves the embryological characteristics of the site of origin: this principle is reflected in the bone density that develops in the regenerated site. Homologous bone supplied by tissue banks in various formulations is an osteoconductive and partially osteoinductive material that guarantees good mechanical properties even in large defects. Heterologous bone of bovine or equine origin is a carbonate-rich non-stoichiometric apatite. Despite showing low resorption, it does not withstand traction or masticatory loading. Alloplastic materials are osteoconductive materials showing different degrees of resorption; they have biomechanical properties and the speed of their resorption varies, depending on their chemical and stoichiometric formulation. The purpose of bone regeneration thus obtained is to allow the insertion of a titanium implant in the site of the regeneration. This alloplastic implant, whose rough and porous surface allows integration with the bone tissue, will support the prosthesis subsequently applied.