## 1 Introduction  
Alteration of the alveolar ridge following tooth extraction is unavoidable owing to horizontal and vertical bone resorption [1]. If the alveolar ridge undergoes extensive bone resorption, it may compromise the aesthetic value and function of dental implants. Considerable alveolar bone alteration has been reported to occur during the first year following tooth extraction [2], and two-thirds of this bone resorption was observed in the buccal part. The bone height decreased by approximately 0.8 mm 3 months after extraction, and continued decreasing to 2 mm after 12 months. In contrast, horizontal width resorption occurred more drastically during the first year following extraction [3; 4; 5]. To overcome these obstacles, various techniques have been proposed to preserve and maintain the alveolar ridge volume following tooth extraction. This includes bone grafting immediately after tooth extraction using bone biomaterials or substitutes to diminish the extent of volume changes [6; 7; 8]. This ridge preservation technique, also known as alveolar socket preservation, socket grafting, or the socket seal technique has been successfully implemented and has been reported to reduce alteration of the socket. A wide range of biomaterials, including autografts [9], allografts [10], xenografts [11], alloplastic materials such as bioactive glasses [12], autogenous tooth bone grafts [13; 14; 15], bioactive materials such as recombinant human bone morphogenetic protein-2 (rhBMP-2) [16], and platelet-rich fibrin (PRF) [17], has been shown to produce positive outcomes for ridge preservation. Autogenous bone is an ideal material for hard tissue defects because it has osteoinduction and osteoconduction and has no immune rejection. However, it has disadvantages in that it causes secondary defects, has a limited amount of harvesting, and inevitable absorption occurs. Allogeneic bone and xenogeneic bone have problems such as infection, immune rejection and high cost. Synthetic bone is considered to be an alternative material, but these materials lack osteoinductive potential, and their osteogenic potential is not satisfactory. Autogenous tooth-derived demineralized dentin matrix (DDM), has a relatively shorter history of clinical adaptation in comparison with other bone grafts or substitutes. The chemical compositions of dentin and bone are very similar. In addition, about 90% of the dentin organic material consists of collagen fiber, which is mostly type I collagen and plays an important role in calcification. The remaining organic parts are composed of noncollagenous proteins including growth factors, carbohydrates, lipid, etc. [18]. In a previous study, a scanning electron microscopy (SEM) analysis of calcified dentin revealed dentinal tubules, which are thought to contribute to the diffusion of nutrients after grafting by acting as a network [19]. Several recent studies have demonstrated that DDM is well-tolerated when used to fill the ridge defects, indicating promising potential for bone regeneration [13; 14; 15; 20]. Similarly, the effectiveness of DDM as a bone substitute has already been identified in various clinical circumstances such as the alveolar bone regeneration associated with dental implants, sinus augmentation, and preservation of extraction sockets [13; 14; 15; 21; 22]. In these studies, DDM completely fulfills the criteria for a bone regeneration material, possessing osteoinductive and osteoconductive properties [23]. Moreover, its clinical safety and capability are well-demonstrated. However, published human data, with respect to the therapeutic efficiency of DDM for ridge preservation, is scarce. Only a few studies have investigated the clinical changes following tooth extraction, and socket management, using DDM [13]. A rhBMP-2 is a potent osteoinductive protein which promotes the differentiation of osteoblasts from mesenchymal stem cells and accelerates bone regeneration [24].