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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 Fig. 1 Fig. 3 Periapical radiograph showing the orthodontic miniscrew. Figs. 4a–c Orthodontic treatment: right (a), left (b) and occlusal (c) view. Fig. 1 Descriptive illustration of the onlay bone grafting procedure. In order to be successful, the three elements must be achieved to ensure a proper creeping substitution process. Va s c u l a r i z a t i o n Biomaterials used in bone regeneration lack cells, proteins and vessels. In this manner, risk of disease transmission is minimized. Therefore, cells from the recipient site of the graft carry out the process of neoangiogenesis, an essential step for successful bone regeneration.22 Neo- vascularization indeed is fundamental because it supplies the avascular scafold with oxygen and the nutrients required for cell growth and differentiation.23 Accordingly, newly formed bone and resorption of the block graft rely upon the neoangiogenesis process. Numerous growth factors, such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), some subgroups of the transforming growth factor beta family (TGF-(cid:697)), transcription factor to induce hypoxia (HIF), angiopoietin (Ang-1), hepatocyte growth factor (HGF), platelet- derived growth factor (PDGF-BB), insulin-like derived growth factor (IGF-1, IGF-2) and neuro- trophic growth factor (NGF) are involved in the process.24 Accordingly, VEGFs and their recep- tors are in charge of the molecular and cellular cascade inasmuch as they lead the development of the endothelial system by vasculogenesis, angiogenesis and the lymphatic net. Addition- ally, VEGFs play a meaningful role in skeletal growth and in bone repair and regeneration.25 Likewise, FGFs are in charge of promoting pro- liferation and diferentiation of endothelial cells and fibroblasts. On the contrary, TGFs increase extracellular matrix development. HIFs mediate the efects of hypoxia on the cells. Ang-1 stabi- lizes the vessels. However, HGFs act on epithe- lial and endothelial cells for organ regeneration and wound healing. Commonly used as exoge- nous growth factors in bone regeneration, the PDGF family plays an important role in angio- genesis. IGFs in contrast have endocrine efects upon the host. Lastly, NGFs, also known as neu- rotrophins, maintain nerve cells within the hor- izontal newly formed bone.26, 27 In bone regeneration using block grafts as scafolds, new tendencies are arising, since, con- trary to autogenous grafts, early neoangiogen- esis is essential for biomaterial survival and in- tegration. In consequence, techniques such as the delivery of stem cells and growth factors in order to accelerate the process have been close- ly examined recently with promising results.28 However, there is still a lack of results to make any conclusive statement in this regard. T y p e s o f b l o c k g r a f t b i o m a t e r i a l s 1. Allogeneic block grafts The use of allografts represents a fair alternative to autogenous block grafts, since the blocks are harvested from the same species as that of the recipient. The first bone allografts were per- formed in late 19th century by a group of sur- geons who reconstructed an infected humerus with a graft harvested from the tibia of the same Journal of Oral Science & Rehabilitation Volume 3 | Issue 1/2017 21