**2. Techniques used in oral surgery to avoid post-extraction bone volume loss or increase sub-sinus bone volume**

Alveolar ridge preservation and maxillary sinus graft techniques are based on filling respectively the empty alveolus or the space between the sinus floor and the Schneider membrane with biocompatible material, with or without adjuncts, with or without a covering membrane.

#### **2.1 Biomaterials used in oral surgery**

Biomaterials used in oral surgery are classified into two categories: Natural origin biomaterials and synthetic origin biomaterials.

#### *2.1.1 Synthetic origin biomaterials*

Synthetic origin biomaterials include tricalcium phosphate, hydroxyapatites, biphasic ceramics, bioactive glasses, and polymers [9]. Tricalcium phosphates (ßTCP) Ca3(PO4)2 are produced by heating a mixture of calcium phosphate powder and naphthalene to over a thousand degrees and under pressure, which, after sublimation, leaves a porous structure that is responsible for the material's osteoconductive properties. Porous hydroxyapatite Ca10(PO4)6(OH)2 is obtained by the thermal transformation of calcium carbonate. Chemically, this calcium phosphate is the closest to biological apatite crystals. Several porosities are available. The higher the porosity, the better the osteoconduction. Biphasic ceramics (BCP) comprise a combination of hydroxyapatite and tricalcium phosphate in varying proportions, allowing the qualities of both materials to be combined, particularly to obtain adequate resorption and mechanical properties. Bioactive glasses, SiO2P2O5CaONaO, are materials known as "bioactive." This "bioactivity" would be due to surface reactions of the bioactive glass and ionic exchanges with biological fluids. The os/bioactive glass bond would be made through a layer of amorphous silica gel that exerts a chemotactic effect on osteoblasts. Polymers, notably polymethylmethacrylate (PMMA), have excellent biocompatibility.
