## 4 Discussion  
The present study aimed to evaluate the beneficial effect of adding HyA to BCP for regeneration of femoral condylar defects in a rat model. Osseous defects grafted with BCP, in the present study, displayed significantly higher new bone formation as compared with the control defects, both at four weeks and at 10 weeks. The addition of HyA to BCP did not improved new bone formation or enhanced BCP resorption. The management of periodontal osseous defects is still a clinical challenge [4]. Primarily, it is because the healing of large bone defects usually requires grafting with a sufficient amount of autogenous bone harvested from a suitable donor site [8]. Alternatively, several types of allogeneic bone grafts, including freeze-dried, demineralized, and fresh frozen cadaveric bone have been used clinically, notwithstanding their associated risk of disease transmission [23]. Similarly, deproteinized xenografts have also been used clinically to treat bone defects, in spite of their biological inferiority to autografts and allografts [4]. Several synthetic bone substitutes have been used in clinical dentistry for regeneration of osseous defects, with considerable success and absolutely no risk of disease transmission [11; 12]. The primary goal of synthetic bone material scaffolds such as calcium phosphate ceramics (CaP) is to augment bone defects and facilitate osteoconductive bone regeneration within those defects [6]. CaP-based biomaterials can undergo ceramolysis leading to their resorption and increasing bioavailability of calcium and phosphorous ions, which together permit new bone matrix formation and its early mineralization [24]. Furthermore, CaP ceramic granules are reportedly capable of adsorbing proteins and growth factors essential for bone regeneration, thereby exerting indirect osteoinductive properties [24]. Nevertheless, research evidence is still inconclusive as to whether CaP bone graft has a sufficient osteogenic ability in large osseous defects [25]. One of the most commonly used CaP ceramics, beta-tricalcium phosphate (\(\beta\)-TCP) undergoes rapid degradation, thereby limiting its ability to promote bone regeneration in large osseous defects and over a longer period of time [24]. However, hydroxyapatite (HA) is known for its slow degradation and presence at grafted bone defect sites even after a very long time [13]. Therefore, biphasic bone substitutes (HA/\(\beta\)-TCP) with a controlled rate of degradation and the ability to promote osteoconductive bone regeneration and remodeling over a longer period of time were considered favorable [12]. BCP composed of HA and \(\beta\)-TCP combines the advantages of rapid degradation of \(\beta\)-TCP for early bone matrix deposition and the persistence of HA for the long term mineralization of the new bone [24]. The results of the present study were coherent to the above findings and revealed minimal inflammatory response associated with BCP grafting along with new bone formation as early as four weeks and persistent remodeling even at 10 weeks. While there has been controversy surrounding the optimum ratio of HA to \(\beta\)-TCP in BCP preparations, [PERSON] et al. [26] reported that HA and \(\beta\)-TCP used in vivo, at concentrations of 60% and 40%, respectively, improved osseous defect healing in dogs. Moreover, they reported that BCP (60% HA + 40% \(\beta\)-TCP) was capable of better recruitment of osteogenic cells and acted as an adequate scaffold for bone regeneration [26]. The BCP combination used in the present study, namely Maxresorb(r), was a porous granulate form (particle size 0.5 to 2 mm), primarily indicated for dental applications. Maxresorb(r) consists of a mixture of 60% HA and 40% \(\beta\)-TCP, [27] and owing to its significant biocompatibility, has been reported to allow direct bone bonding without development of an intervening soft tissue layer [11; 12].