الفهرس 
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Abstract
In early years of modern implantology, the chief concern was tissue health and implant survival. But now there has been an increasing appreciation that esthetic is just as important to success of the final restoration as health. Replacement of lost teeth by implants has revolutionized rehabilitation while significantly advancing restoration dentistry.( El Askary et al 2001) Consequently, many recent studies have focused on treatment outcome of implant therapy performed in the esthetic zone. Placement of dental implant in the esthetic zone is a technique sensitive procedure with a little room for error (Al-Sabbagh et al 2006). Yet challenges remain in many cases. Inadequate bone availability for implant placement and optimal esthetic outcomes are common issues facing clinicians. However, certain cases have undergone such extensive bone and soft tissue destruction that implants cannot be placed immediately and hard and/or soft tissue augmentation is required prior to implant placement (Jivraj et al 2006). Successful implant therapy still can be attained in a resorbed ridge through a wide range treatment options, including Block grafts, guided bone regeneration, and placement of narrower width or shorter length implants (Cyril et al 2011) .
In the process of tissue repair and restoration, the osseointegration of dental implant can be improved and accelerated by increasing the regenerative capacity of surrounding tissues with the appropriate stimuli (DuRaine et al 2011). Because growth factors are expressed during different phases of tissue healing, it has been thought that they could
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serve as therapeutic agents to promote tissue regeneration. (Anitua, E. 2006). Platelet-rich plasma (PRP), platelet-rich concentrate, autologous platelet gel or platelet releasate, all refer to one concept (1) which is an autologous concentration of human platelets contained in a small volume of plasma. It is known for a long time that fibrin clot and platelets have haemostatic and tissue repairing effect. In 1975, an article was published with the concept of platelet gel under the title of: ‗use of platelet-fibrinogen-thrombin mixture as a corneal adhesive’(Marx et al 1998). An exciting report was published in 1979 about the usage of gel foam in sutureless nerve anastomosis. After a few years an animal model showed that platelets and fibrin initiate a process consist of cell migration, collagen synthesis, fibroplasia and angiogensis which helps the lesion healing. The real application of platelet releases in treating wounds has begun in the mid-1980s after publication of (Kingthon et al. in 1986). In 1997 another important report was published about the maxillofacial surgery and platelet gels. The usages of platelet gel became more popular in late 1990s, after the publication (1998) of a paper about the effectiveness of the platelet-rich plasma (PRP) in bone regeneration in the field of dental care. (Banihashemi, 2014).
Platelet Rich Fibrin (PRF) was first developed in France by Choukroun. for specific use in oral and maxillofacial surgery. This technique requires neither anticoagulant nor bovine thrombin (nor any other gelling agent) compared to cPRP (concentrated platelet rich plasma). It is nothing more than centrifuged blood without any addition, which makes it possible to
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avoid all the restrictions of the French law related to blood-derived product reimplantation ((Dohhan et al.2009). Early publications and clinical experience seem to indicate that PRF improves early wound closure, maturation of bone grafts, and the final esthetic result of the peri-implant and periodontal soft tissues. The clinical experience confirms that PRF can be considered as a healing biomaterial. It features all the necessary parameters permitting optimal healing. These consist of a fibrin matrix polymerized in a tetra molecular structure, the incorporation of platelets, leukocyte, and cytokines, and the presence of circulating stem cells (choukroun et al. 2006). Despite the fact that cytokines trapped in PRF are gradually released and able to accelerate the cellular phenomenon, the structure of the fibrin network is the key element of all improved PRF healing processes. Finally, from a clinical standpoint, this biomaterial appears to accelerate physiologic healing. Cytokines play significant role in the delicate balance of tissue homeostasis. cPRP and now PRF open a new research opportunity for the comprehension of these technologies, because the PRF is not only platelet concentrate but also immune node able to stimulate defense mechanism. It is even likely that the significant inflammatory regulation noted on surgical sites treated with PRF is the outcome of the retro control effect from cytokines trapped in the fibrin network and released during the remodeling of this initial matrix (Chokroun et al 2006).
A protocol has been developed for the practical and predictable application of growth factors-assisted regeneration therapy. The technique is relatively simple
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to implement, and the result can be consistently reproduced on an outpatient basis. This treatment consists of the direct application of concentrated plasma growth factors known as plasma-rich growth factors (PRGF) within the defect. Autologous Plasma Rich in Growth Factors (PRGF) have been shown to enhance and accelerate soft tissue repair and bone regeneration in preparation of future sites for dental implant (Anitua et al 2006). A preparation of PRGF applied to a titanium implant adheres to the metal and might create a new dynamic surface that could potentially show biological activity. This protein layer consists of a fibrin net embedded with growth factors that covers the whole implant surface and transform the initial interactions of the implant surface with the surrounding tissues. It also influences cellular attachment proliferation and differentiation, and bone matrix deposition. This coating has two important properties that may contribute to optimizing and accelerating the osseointegration process: the osseoconductive properties of fibrin and osteoinductive activities of growth factors. So, it was important to study the adherence of PRGF to implant surface and its permanence after clot restriction. Taking in consideration that PRGF coated surfaces could accelerate implant osseointegration was tested in an animal model. In view of the good experimental results obtained, it was hypothesized that the clinical use of implant surfaces coated with PRGF would improve the outcome (Anitua et al 2006). Plasma Rich in Growth Factors (PRGF-Endoret) technology is an autologous platelet-enriched plasma obtained from patients own blood ,which after activation with calcium chloride allows the release of a pool of biologically active proteins, growth factors and biomaterial scaffolds for therapeutic purposes, that influence and promote a range of biological
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processes including cell recruitment, growth and differentiation (Anitua et al 2011). This technology provides a new approach for the stimulation and acceleration of tissue healing and bone regeneration .The versatility and biocompatibility of using patient-derived fibrin scaffold as an autologous, biocompatible and biodegradable drug delivery system open the door to personalized medicine that is currently being used in numerous medical and scientific fields including dentistry ,oral implantology, orthopedics, ulcer treatment, sports medicine and tissue engineering among others (Anitua et al 2011). More recently, preparation with PRGF-Endoret has been shown to enhance postoperative healing of ruptured Achilles tendon in professional athletes and articular cartilage repair after non traumatic avulsion (Sánchez, M. et al 2007). This study focused upon which the effect of different platelet concentrates on the soft and hard tissue regeneration and wound healing around immediate implant placement.