During the last decades, implant rehabilitation received increasing attention in odontostomatology, offering a real and practical alternative to conventional prostheses.
The enthusiastic intention to treat edentulous areas with endosseous implants has often clashed with the assumption that the loss of teeth is reflected in a progressive bone reabsorption. In particular, the lateral and posterior parts of the edentulous upper jaw often present some anatomical limitations, resulting in a continuous challenge for the dental surgeon.
In such areas, in fact, the primary stability of implants, as well as the elusion of intra- and post-operative complications, may be invalidated by an inadequate three-dimensional
bone support, that is to say an insufficient height and/or thickness of the alveolar crest.
This bone deficiency may result from an excessive pneumatization of the maxillary sinus (large sinus cavities), from an important atrophy of the alveolar crest referable to dental extractions andor periodontal diseases, or from both of these causes. Besides, the reabsorption process, in edentulous posterior maxillary regions, could determine insufficient vertical dimensions for the implant positioning, often requiring additional surgical procedural steps.
These involve the use of:
- Reabsorbable and not-reabsorbable membranes;
- Bone substitutes often combined with autologous
- Surgical expansion through Le Fort I Osteotomy
with interposition of bone grafts;
- Sinus lift procedures with the contextual filling of the cavity by means of several graft materials.
This property is expressed only in case of autogenous grafts, which are the only ones able to provide the necessary cellular elements:
these are contained in the bone marrow to a greater extent, and then in the intracortical region and in the periosteum.
Bone Grafting Materials
The bone grafting materials are commonly classified as follows: Autologous grafts (or autografts), coming from the same individual and taken from:
• Intraoral donor sites (greenstick grafts and bone fragments taken from the tuber, the chin area and the edentulous saddle area);
• Extraoral donor sites (bone fragments taken from the tibia, the rib and the iliac crest).
The suitable grafting material was the autologous bone from an intraoral source, due to the same embryogenetic derivation and for the presence of the bone morphogenetic protein (BMP),
which promotes osteoinduction.
The autologous bone represents an ideal material for sinus lift, because it is the only material presenting osteogenic properties, in addition to the osteoinductive and osteoconductive ones. From the histological point of view, the autologous bone looks similar to that of the host bone, being surrounded by newly formed bone and with its reabsorption process very slow. Histomorphometric
analyses, performed in a few studies, reveal a percentage of newly formed bone around 40%.
Some limit in using the autologous bone procedure is the operating time together with the necessity to operate on two areas of the body.
Therefore, in clinical practice, the allogenic or alloplastic materials result more used9-10.
• Homologous grafts, coming from another individual of the same species;
• Heterologous grafts (or xenografts), coming from another individual of a different species,
which in general is bovine, demineralized, sterilized or frozen. Due to the absence of living osteoblasts, the allogenic bone cannot cause osteogenesis, but only osteoinduction and osteoconduction. One of the main features to take into account, while choosing the material, is the time span at which the biomaterial is reabsorbed. Obviously, slow reabsorption is more desirable, compared to a reabsorption process which is too fast, because the latter would not lead to new bone formation into the newly formed matrix. Rapid phenomena, infact, would inhibit revascularization and con-
tinuous bone remodeling, necessary to assure osteoconduction and osteoinduction.
Brunsvold and Mellonig defined the range between 250 and 270 as the dimensional range which the microarchitecture of a biomaterial should always comply with, in order to ensure an optimum reabsorption time and, therefore, promote osteoinduction and osteoconduction11. Smaller or larger sizes are not desirable, as reabsorption would be too fast and too slow, respectively.
Deproteinized bovine bone (Bio-Oss) is frequently used in the clinical practice of sinus lift, being it able to induce a physiological bone remodeling, with disposition and significant bone gain, thanks to its chemical-physical properties which are very similar to those of the human bone (the percentage of newly formed bone is around 39%). Apart from its good osteoinductive and osteoconductive properties and the poor reabsorbability, the bovine bone mineral does not run intolerance or infection risks.
The biocompatibility of the material is due to its preparation, aiming to eliminate protein and lipid components from the original material, making it inorganic before being sterilized by heat and
Demineralized Bone (DFDBA, Demineralized Freeze-Dried Bone Allograft) DFDBA is obtained by treating a human bone sample from donor sites (24 hours before death) with a process of demineralization with hydrochloric acid, water washing, drying, sterilization, irradiation and freezing. In this way, the organic matrix remains intact and proteins like BMP are exposed, responsible for the osteoinductive properties of DFDBA. The good quality and quantity of bone regeneration, achieved by means of demineralized freeze-dried bone allografts, has been confirmed by several recent studies.
Alloplastic grafts made up of synthetic materials.
Hydroxyapatite (HA) Hydroxyapatite (Ca10(P04)(OH)2) is a calcium phosphate ceramic, which in nature represents 60-70% of bone and 98% of enamel. HA is a bioinert material which binds the bone, without provoking inflammatory and/or toxic reactions and shows osteoconductive properties, as it serves as a matrix for the migration of osteogenic cells within it16. It is commercially available in several forms, presenting different physicalchemical properties, such as:
• Forms of product distribution (blocks or particles);
• Porosity (dense, microporous, macroporous);
• Crystallinity (crystalline, amorphous).
For implant insertion, it is recommended to use the microporous form, characterized by an ideal reabsorption time, in order to guarantee osteoconduction and, therefore, implant osteointegration.
Calcium sulphate, in its hemihydrate form, has been extensively used, both in the medical treatment by implants and in periodontics, for bone and periodontal regeneration.
Periodontal regeneration is confirmed by the results of experiments in both animal and human models. With regard to bone regeneration, a study on animal models confirmed the possible use of
calcium sulphate as a barrier to employ according to the principles of Guided Bone Regeneration (GBR). Calcium Sulphate (CaS), also known as plaster of Paris, is made up of sulphuric acid and
calcium; there a re thre e differe nt hydr ation forms: anhydrate,hemihydrate, and dihydrate17.
In case of sinus lift, its frequently used form is called Surgiplaster Sinus, that is calcium sulfate with a mean granulometry, specifically used for maxillary sinus lift because, thanks to its particular granulometry, it can be easily placed and also modulates reabsorption according to the [continue in the integral article]