Healing of rabbit calvarial bone defects using biphasic calcium phosphate ceramics made of submicron-Sized grains with a hierarchical pore structure

Objectives: This study investigated the efficacy of new bone graft substitutes - biphasic calcium phosphates (BCP) made of submicron-sized grains with fully interconnected wide-range micron-scale pores in two different macrodesigns: donut shaped with a 300-400 μm central macropore (n-BCP-1) or rod-shaped (n-BCP-2) - in the healing of rabbit calvarial defects, and compared their bone-healing properties with those of various commercial bone substitutes, which included substitutes with similar BCP composition (MBCP and Osteon), anorganic bovine bone (Bio-Oss), and β-TCP (Cerasorb). Material and methods: The surface morphology of the bone substitutes was investigated using scanning electron microscopy (SEM). Defects 8 mm in diameter were created in the calvaria of 30 adult male New Zealand White rabbits and were filled with six types of bone substitutes. The percentage of newly formed bone (NB%) was evaluated histomorphometrically 4 and 8 weeks after implantation. Results: SEM observation showed submicron-sized grains with fully interconnected micropore structures in the n-BCP-1 and n-BCP-2 groups; these groups also showed considerable new bone formation in inner micropores as well as on the outer surfaces. The n-BCP-1 group exhibited enhanced new bone formation and direct ingrowth of bone tissue with blood vessels into central pores. Histomorphometric analysis showed significantly greater NB% in the n-BCP-1 group when compared with the other groups at 4 and 8 weeks (P<0.05). Conclusion: A new BCP ceramics made of submicron-sized grains with a hierarchical pore structure was an effective osteoconductive material for the treatment of osseous defects of rabbit calvaria.