Abstract
BackgroundIt has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. Bone morphogenetic protein-2 (BMP-2) has been shown to be a promising alternative to bone grafting and a therapeutic agent promoting bone regeneration when delivered locally. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (β-TCP) cylinders and local BMP-2 administration on β-TCP resorption and new bone formation.MethodsBilateral cylindrical bone defects were created in rabbit distal femora, and the defects were filled with β-TCP. Rabbits were divided into 3 groups; defects were filled with a β-TCP cylinder with a total of approximately 60% porosity (Group A: 13.4% micro- and 46.9% macropore, Group B: 38.5% micro- and 20.3% macropore, Group C: the same micro- and macro-porosity as in group B supplemented with BMP-2). Rabbits were sacrificed 4, 8, 12, and 24 weeks postoperatively.ResultsThe number of TRAP-positive cells and new bone formation in group B were significantly greater than those in group A at every period. The amount of residual β-TCP in group C was less than that in group B at all time periods, resulting in significantly more new bone formation in group C at 8 and 12 weeks. The number of TRAP-positive cells in group C was maximum at 4 weeks.ConclusionsThese results suggest that the amount of submicron microporous structure and local BMP-2 administration accelerated both osteoclastic resorption of β-TCP and new bone formation, probably through a coupling-like phenomenon between resorption and new bone formation.
Highlights
It has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction
Beta-tricalcium phosphate (β-TCP) is a calcium phosphate (CaP) ceramic used in bone grafting as an alternative bone substitute to autograft
tartrate-resistant acid phosphatase (TRAP)-positive cells were in contact with the surface of β-TCP cylinders in all groups at 4 weeks, but the number of TRAP-positive cells in group A was smaller than that in groups B and C at 4 weeks (Fig. 3). β-TCP resorption and new bone formation occurred at the periphery of the β-TCP cylinders at 4 weeks in all groups and progressed toward the center of the β-TCP cylinders in a time dependent manner in all groups
Summary
It has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (β-TCP) cylinders and local BMP-2 administration on β-TCP resorption and new bone formation. Beta-tricalcium phosphate (β-TCP) is a calcium phosphate (CaP) ceramic used in bone grafting as an alternative bone substitute to autograft. The β-TCP block with 75% porosity that we have used can be resorbed within a few years. It has been reported that the microporous structure of CaP ceramics is important to osteoconduction [9,10,11,12,13,14,15,16]. It was reported that CaP ceramics without micropores were not resorbed and there was slower bone ingrowth compared with those that had micropores [18]
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