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, beta-calcium pyrophosphate (Ca2P2O7), beta-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 microns) 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.