Transmission electron microscopy observations at the interface of bone and four types of calcium phosphate ceramics with different calcium/phosphorus molar ratios

Four kinds of calcium phosphate ceramics, β-calcium pyrophosphate (Ca2P2O7), β-tricalcium phosphate (Ca3(PO4)2), hydroxyapatite (Ca10(PO4)6(OH)2) and tetracalcium phosphate (Ca4(PO4)2O), were prepared. The calcium/phosphorus molar ratios were 1,1.5, 1.66 and 2, respectively. Particles (150–300 μm) of these ceramics were packed into holes (diameter 2.5 mm) made in the tibial metaphysis of mature male rats. At 2 weeks, 4 weeks, 8 weeks and 6 months after the operation, undecalcified specimens were prepared. Transmission electron microscopy showed that the bone-bonding behaviour of calcium phosphate ceramics at the interface with bone did not vary with the calcium/phosphate molar ratio. Amorphous substances or needle-like microcrystals were observed on the surface of the ceramics at 2 weeks after implantation. The ceramics showed direct continuity with small crystallites of bone tissue at 4 weeks, 8 weeks and 6 months after implantation. The ceramics appeared to be getting smaller with time. Collagen fibres were not observed at the bone/ceramic interface. Neither chemical bonding nor mechanical bonding by interlocking between bone and ceramics was described by morphological observation using transmission electron microscopy.