**5. Types of bone grafting materials**

Graft materials may be synthetic or natural materials that are placed in a biological environment for reconstructive purposes, and are prepared to be accepted by the surrounding tissues. The most commonly used biomaterials include autografts, xenografts, allografts, and alloplasts. Ideally, the material for bone regeneration should be able to form a new bone, and the formation of the new bone should balance with resorption [36].

The first biomaterials used for grafting areas with bone deficiencies were autografts. Autogenous bone is considered the gold standard for grafting biomaterials for its three main properties: osteogenesis, osteoinduction, and osteoconduction. Advantages of autogenous bone grafts include early vascularization, osteoinductive properties, low cost, and minimal morbidity. Recent research on cortical bone chips revealed that the paracrine effect of bone chips has a significant impact on bone regeneration. Autogenous bone can be harvested near the receiving site to reduce morbidity. Using a bone scraper may reduce the treatment time and simplify harvesting of the autogenous bone [37].

Calcium phosphate ceramics can be both osteoinductive and osteoconductive. Osteoinductivity occurs with the formation of a hydroxyapatite (HA) layer immediately after implantation. Ca2 + and PO4 ions required to form this layer are removed from the bone surrounding the graft. With excellent biocompatibility and without systemic toxicity or foreign body reactions, calcium phosphate ceramics are promising biomaterials that require further clinical investigation. Synthetic hydroxyapatite is one of the most commonly used alloplastic materials because of its chemical composition, which is similar to the human bone. It is nontoxic, has high chemical stability, and causes less inflammation and antigenic reactions. Another important property of HA is that the microstructure can be controlled to induce the formation of pores in the material that permits the migration of new bone tissue and blood vessels. Clinical applications, such as bone defect repair, alveolar ridge preservation after tooth extraction, ridge augmentation, and sinus grafting possibly combined with autogenous bone, are possible with HA [36].

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Tricalcium phosphate (TCP) is a biocompatible and bioabsorbable material. However, due to rapid dissolution within 6 weeks, it is not an optimal bone substitute in terms of space maintenance. It is similar to the mineral structure of the bone in terms of its chemical composition and crystal structure. It follows similar healing steps with other graft materials. The known

Various types of membranes have been used for tissue regeneration, with the aims of support and maintenance of the treatment area. The barrier membrane allows the migration of regenerative cells within the confinement area, while this technique prevents the migration of undesired cells into the wound area. There are two main groups of membranes: resorbable

Graft materials have been used with resorbable membranes for guided bone regeneration. Ever since resorbable membranes have no stable fixed shape, it is feasible to utilize them for GBR. Resorbable membranes that are developed nowadays are prepared from glycosides and lactic polymers. Absorption of these membranes by hydrolysis takes a minimum of 6 weeks and is completed in exactly 8 months. Traditional resorbable membranes, using polymers like polylactic acid, demonstrated therapeutic problems due to their inflammatory properties and reaction to foreign bodies upon degradation. Due to premature membrane resorption, minimal inflammatory reaction may occur, but clinical observations show that the inflammation does not prevent healing. Resorbable membranes possess qualities such as low possibility of complication, membrane subtraction after healing, reduced morbidity, and easy manipulation. These types of membranes as effective as conventional expanded polytetrafluoroethyl-

Polymers have had long and widespread use as biomaterials. Resorbable polymers have a remarkable advantage since they do not require a second operation after implant placement.

disadvantages of TCP are indicated as unpredictable and rapid resorption rate [19].

**6. Membranes**

and nonresorbable.

**6.1. Resorbable membranes**

ene (e-PTFE) in recent experiments [37].

Allografts are bone grafts collected for transplantation purposes from one person to another and have widespread use. They are important for the treatment of congenital, traumatic, degenerative, and neoplastic bone defects. The advantages of allografts include availability and reduced morbidity, since harvesting bone from an intraoral site is no longer required. The main disadvantage is the possibility of transmission of infection from the donor to the recipient. Possible transmittable infections include malignant neoplasms, degenerative bone diseases, hepatitis B, hepatitis C, and HIV. Donors are carefully screened, and graft materials are meticulously processed to reduce disease transmission. Allografts are not osteogenic and thus, healthy bone formation takes longer compared to that with autogenous bone grafts. There are two main forms of allografts: mineralized freeze-dried bone allografts (MFDBA) and DFDBA. In FDBA, the graft is dried at low temperatures throughout the entire process. In DFDBA, the mineralized phase of MFDBA is removed so that collagen and BMPs are exposed. If this mineral phase is not removed, the bone induction process is not observed. MFDBA is mainly used for its osteoconductive properties and space maintenance. Cortical bone chips are generally preferred for allografts because of their low antigenic activity and high levels of collagen [36].

Grafts obtained from a donor in a different species are xenografts (also called heterogeneous grafts). Xenografts are composed of deproteinized spongiform bones naturally obtained from other species such as horses or cows. Heterogeneous bone grafts have been proposed to fill bone defects; many clinicians have reported that these grafts have little to no osteogenic potential and may instead be used as scaffolds for space maintenance and long-term bone formation. Bovine bone is the best and most commonly preferred source of xenografts. The risk of transmission of diseases, such as spongiform encephalopathy in cattle, is insignificant due to the grafts deproteinization process. Inorganic and protein-free bones are materials in which only the natural calcium phosphate in the bone is retained. This material consists of unsaturated calcium apatite crystals, and provides long-term low resorption space maintenance, shown to remain 10 years postoperatively. Xenografts inhibit resorption of the grafted site but may negatively impact healing by decreasing the rate at which the implant surface area is integrated with the newly formed bone. Used in cystic cavities, alveolar ridge augmentation, extraction sites for implant placement, and sinus lifting, xenografts are viable materials, when a high osteogenic potential is not imperative. Xenografts can also be mixed with autogenous bone grafts. Such a composite graft material with osteogenic properties can be successfully used for horizontal and vertical ridge augmentations [19].

Alloplastic biomaterials are synthetic graft materials. Biocompatible synthetic graft materials have been used for the last two decades to avoid the disadvantages of allografts and xenografts. Alloplastic materials are not osteoinductive, but they can provide space maintenance and act as a scaffold for new bone formation; this means that they are osteoconductive. Advantages of alloplastic materials include being risk free in terms of cross infection, their availability, being sterilizable, and their biocompatibility. Alloplasts used in augmentations are solid or porous polymers, hydroxyapatite (HA), and calcium triphosphate ceramics, or combinations of these materials [20].

Calcium phosphate ceramics can be both osteoinductive and osteoconductive. Osteoinductivity occurs with the formation of a hydroxyapatite (HA) layer immediately after implantation. Ca2 + and PO4 ions required to form this layer are removed from the bone surrounding the graft. With excellent biocompatibility and without systemic toxicity or foreign body reactions, calcium phosphate ceramics are promising biomaterials that require further clinical investigation. Synthetic hydroxyapatite is one of the most commonly used alloplastic materials because of its chemical composition, which is similar to the human bone. It is nontoxic, has high chemical stability, and causes less inflammation and antigenic reactions. Another important property of HA is that the microstructure can be controlled to induce the formation of pores in the material that permits the migration of new bone tissue and blood vessels. Clinical applications, such as bone defect repair, alveolar ridge preservation after tooth extraction, ridge augmentation, and sinus grafting possibly combined with autogenous bone, are possible with HA [36].

Tricalcium phosphate (TCP) is a biocompatible and bioabsorbable material. However, due to rapid dissolution within 6 weeks, it is not an optimal bone substitute in terms of space maintenance. It is similar to the mineral structure of the bone in terms of its chemical composition and crystal structure. It follows similar healing steps with other graft materials. The known disadvantages of TCP are indicated as unpredictable and rapid resorption rate [19].
