**2. Translational studies**

beginning of the nineteenth century. In this regard, Albee in 1915 had depicted that there were successfully bone transplants in animal models, as well as in humans, since 1809 [2]. Nowadays, bone graft implantation is the main treatment modality for bone defect repair and reconstruction [3]. In oral and maxillofacial areas, bone grafting aims to replace the volumetric bone loss that frequently occurs by systemic pathologies, periodontal defects, and tooth loss [4]. The mechanisms underlying the bone healing promoted by a bone graft are osteogenesis (osteodifferentiation and subsequent new bone formation by donor cells derived from the host or graft), osteoinduction (induction of undifferentiated and pluripotent cells to develop osteogenesis into the bone-forming cell lineage), and osteoconduction (the ability to support the attachment of osteoblast and osteoprogenitor cells and the migration and ingrowth of these cells within the three dimensional architecture of the graft) [5, 6], in combination or alone [7]. Bone grafting materials are classified as autografts (derived from the same individual), allografts (derived from a different individual from the same species), xenografts (derived from a different species), and alloplasts (derived from synthetic sources) [8]. Autografts are the "gold standard" in the reconstruction of bone defects due to their osteoconductive as well as osteoinductive properties [9]. Although they present excellent biological outcomes, they also have a number of drawbacks. In this regard, the use of autografts increases the operative time due to graft harvest, increases the donor site morbidity, and increases the graft resorption. In addition, they represent a big challenge for the operator, since they need to be mold and have limited availability, especially in the pediatric population [10]. Allografts are typically obtained from human cadavers and require to be processed before being used [11, 12]. Allograft bone is available as cortical, cancellous, corticocancellous forms, or as demineralized bone matrix. They can be processed as mineralized or demineralized, fresh, fresh-frozen, or freeze-dried forms [13, 14]. Among the benefits of allografts are their availability in different shapes and sizes. This is particularly advantageous, since it avoids donor site morbidity [15]. The major disadvantages of allografts are related to the transmission of diseases and the graft rejection. In order to decrease the risk of transmitting infectious diseases, allografts need to be treated. The techniques employed include treatment with hypotonic solutions, acetone, ethylene oxide, or gamma irradiation that may eliminate cellular and viral particles [16]. However, these processes eliminate the bone cells and denature proteins present in the graft altering the osteoconductive and osteoinductive properties and eliminating the osteogenic properties [17]. In addition, allografts are capable to induce immunological reactions that interfere with the bone healing process leading to rejection of the graft [15, 18–20]. Xenografts are frequently derived from bovine, porcine, and coral sources [7]. The effectiveness of different bone processing techniques has made possible the use of these materials for medical applications [21, 22]. Bovine bone is one of the most popularly used xenografts. This source material is desirable because it is readily available an inexpensive. However, bovine bone grafts require proper preparation to avoid risks such as transmission of zoonoses [23]. Several studies have shown that organic or inorganic matrix derived from bovine bone is biocompatible and osteoconductive [23, 24]. These important biological properties allow the apposition of newly formed bone by osteoprogenitor cells and the partial remodeling by osteoclasts and osteoblasts of the host [25]. Moreover, the large interconnecting pore volume and its composition encourage the formation and ingrowth of new bone at the implantation sites. Ideally, a synthetic bone graft should be biocompatible and causes minimal fibrotic changes [26]. Synthetic bone grafts

74 Bone Grafting - Recent Advances with Special References to Cranio-Maxillofacial Surgery

We evaluated and compared the effects of a bovine bone graft made in Argentina with a commercial bovine bone graft recognized for its osteoconductive effects, on bone healing process in experimental models in rats (experiment 1) and rabbits (experiment 2).
