# Octacalcium Phosphate Bone Substitute (Bontree(r)): From Basic Research to Clinical Case Study
## 4 Discussion  
In this study, the safety and efficacy of Bontree(r) for bone regeneration were demonstrated using in vitro and in vivo experiments. In addition, in patients with bony defects in the alveolar ridge or maxillary sinus, oral rehabilitation using dental implants was possible after ridge or sinus augmentation using Bontree(r). Although OCP is a promising bone graft material with excellent biological properties, there are only a few commercially available OCP-based products, such as Ti-Oss(r) (Chiyewon, Guri, Korea) or BonarcTM (Toyobo Co. Ltd., Osaka, Japan) bone grafts. However, even these products are not fully composed of Ca- and P-containing apatites; rather, they consist of a combination of OCP with naturally occurring bovine bone materials or collagens. In contrast, the recently introduced OCP bone graft, Bontree(r), is fully composed of apatite compounds with 80 wt.% OCP and 20 wt.% HA, and it exhibits a commercially acceptable quality, defect-free homogeneous surface morphology, and relatively uniform size distribution (Figure 1A). In addition, numerous micron-scale crystals covering the entire surface of Bontree(r) granules are beneficial for increasing the rate of dissolution and resorption of Ca and P ions under physiological conditions, thereby enabling active mineralization on their surfaces. Short-term in vitro and long-term in vivo studies were performed to investigate the bone formation ability of Bontree(r). In the in vitro experiments, RANKL and ALP were used as key markers for bone formation. RANKL is a transmembrane protein that controls the differentiation, maturation, and activation of osteoclasts, which results in bone resorption during remodeling, whereas ALP is an enzyme secreted by osteoblasts and is involved in the mineralization and calcification of newly formed bone tissues. Therefore, the suppressed RANKL activity of MG63 cells is closely associated with reduced osteoclastic differentiation and bone resorption, while the improved ALP activity indicates better osteoblastic differentiation and new bone formation on the bone grafts [19; 25; 26]. If the bone graft material has insufficient ability to regenerate bone tissues, pores between the bone grafts allow infiltration of soft tissues that hinder the formation of new bone [27; 28]. Moreover, the soft tissue is unable to provide sufficient mechanical support to the host bone and prevents the escape of bone grafts from the implanted site [29]. As shown in Figure 2A,B, Bontree(r) exhibited significantly higher values of ALP activity than MBCP+TM at 12 days of MG63 cell culturing, and a significant amount of newly formed bone tissues appeared uniformly distributed over the entire region of the Bontree(r) 0.5-granule- and Bontree(r) 1.0-granule-grafted tibial defects at 4 weeks after surgery. In previous studies, OCP showed outstanding osteoconductive and osteoinductive properties owing to its unique physicochemical properties [30]. When degraded and converted to HA, it releases numerous inorganic PO4\({}^{3-}\) and Ca2\({}^{+}\) ions, which are known to promote osteoblastic differentiation and maturation better than HA, as evidenced by the increased ALP activity (Figure 2B) [31]. In addition, OCP is beneficial for the adsorption of bone-forming molecules and proteins, which could further increase the osteogenic differentiation of cells and initiate bone regeneration [32]. In terms of the size effect of bone grafts on bone regeneration, macroscopic bone grafts generally provide more free space than their microscopic counterparts for cells to move into and attach to, thereby promoting vascularization and ingrowth of newly formed bone tissue into the bone grafts [33]. As shown in Figure 3A,B, Bontree(r) 1.0-granule was associated with greater amounts of newly formed bone tissues than the Bontree(r) 0.5-granule at both 4 and 12 weeks.