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B i o m a t e r i a l s f o r o n l a y b o n e g r a f t s (((((((("alveolar bone loss"[MeSH Terms] OR "alveolar bone loss"[MeSH Terms]) AND bone graft[Title/Abstract]) AND block[Title/Abstract]) OR onlay[Title/Abstract]) AND biomaterial[Title/Abstract]) OR allogeneic[Title/Abstract]) OR allograft[Title/Abstract]) OR xenogeneic[Title/Abstract]) OR xenograft[Title/Abstract] AND "humans"[MeSH Terms] Additionally, a manual search of periodontics- and implantology-related journals, including the Journal of Dental Research, Journal of Clinical Periodontology, Journal of Periodontology, and International Journal of Periodontics and Restor- ative Dentistry, from January 2015 up to June 2016, was performed to ensure a thorough screening process. Furthermore, references of included articles were screened to check all available articles. B i o m a t e r i a l s ’ p r o p e r t i e s “Biomaterial” refers, generally speaking, to ma- terial that has been developed to interact with the biological system, acting as a scafold for replacement and repair of, in this case, lost bone. Firstly, a biomaterial must be biocompatible, which is defined as the capacity that the materi- al has to elicit an appropriate biological response and, thus, not be detected as a foreign body by the host. In addition, it must have suficient du- rability to carry out the task for which it was de- veloped. Further, it must be chemically stable (neither toxic nor carcinogenic for the host). For block grafts used in regeneration, an ideal biomaterial, from the cellular and mo - le cular standpoint, must have the following properties: – Its design enables osteogenic cells to reach the entire block by osteoconduction and osteoin- duction in order to complete the turnover pro- cess. In order to permit osteoblastic growth and mineralized tissue production, the ideal size of the micropores should be within 180–600 μ.19 This is of crucial importance inasmuch as os- teoblasts (15–50 μ) and stem cells (5–12 μ) have to proliferate guided through the pores.20 The biomaterial itself must be replaced by vital bone (newly formed bone). Therefore, the biomate- rial’s degradation must be in accordance with the remodel ing process. – The trabeculae-like structures that form the scafold must leave enough space for the for- mation of new vessels by the endothelial cells that will supply of all the nutrients and osseous cells to the scafold. Therefore, as occurs in autogenous bone blocks, biomaterials undergo three steps: (1) coloni zation of host cells; (2) degradation of the biomaterial while turnover is occurring; and (3) maturation of the newly formed bone and integration with the recipient site’s bone (Fig. 1). However, biomaterials in bone grafting must fulfill other properties besides biological ones. This will allow the material to interact with the host environment and, thus, increase the possi- bility of bone formation and long-term stability. These properties should include: – Mechanical properties: Among these proper- ties are resistance, resilience, stifness, fragil- ity, tenacity, ductility and malleability. The result of the combination of these mechanical properties will determine the handling of the material more than its capacity as scafold for bone regeneration.21 However, it is important to note that, generally, the stifer the bioma- terial is, the longer it lasts due to the more rigid element. – Surface phenomena: It is important to take into consideration the internal energy, surface tension, wettability, and adhesion and cohe- sion of the biomaterial to be used for bone regeneration. These properties are in part responsible for the aggregation and attach- ment of vital osteogenic cells in a nonvital structure (scafold).21 – Physical properties: Three main properties are included within this group: – Thermals: thermal expansion, thermal con- traction, thermal insulation, melting point and interval; – Electrics: electric conductivity, electrical resistivity and oral galvanism; and – Optics: color and appearance. – Chemical properties: toxicity, chemical stabil- ity, half-life, flammability or enthalpy of for- mation among others. – Rheological properties: apparent viscosity, normal force coeficients, storage modulus, complex viscosity and complex functions of nonlinear viscoelasticity. 20 Volume 3 | Issue 1/2017 Journal of Oral Science & Rehabilitation