Physical and Histological Comparison of Hydroxyapatite, Carbonate Apatite, and β-Tricalcium Phosphate Bone Substitutes.

Three commercially available artificial bone substitutes with different compositions, hydroxyapatite (HAp; Neobone), carbonate apatite (CO₃Ap; Cytrans), and β-tricalcium phosphate (β-TCP; Cerasorb), were compared with respect to their physical properties and tissue response to bone, using hybrid dogs. Both Neobone (HAp) and Cerasorb (β-TCP) were porous, whereas Cytrans (CO₃Ap) was dense. Crystallite size and specific surface area (SSA) of Neobone (HAp), Cytrans (CO₃Ap), and Cerasorb (β-TCP) were 75.4 ± 0.9 nm, 30.8 ± 0.8 nm, and 78.5 ± 7.5 nm, and 0.06 m²/g, 18.2 m²/g, and 1.0 m²/g, respectively. These values are consistent with the fact that both Neobone (HAp) and Cerasorb (β-TCP) are sintered ceramics, whereas Cytrans (CO₃Ap) is fabricated in aqueous solution. Dissolution in pH 5.3 solution mimicking Howship's lacunae was fastest in CO₃Ap (Cytrans), whereas dissolution in pH 7.3 physiological solution was fastest in β-TCP (Cerasorb). These results indicated that CO₃Ap is stable under physiological conditions and is resorbed at Howship's lacunae. Histological evaluation using hybrid dog mandible bone defect model revealed that new bone was formed from existing bone to the center of the bone defect when reconstructed with CO₃Ap (Cytrans) at week 4. The amount of bone increased at week 12, and resorption of the CO₃Ap (Cytrans) was confirmed. β-TCP (Cerasorb) showed limited bone formation at week 4. However, a larger amount of bone was observed at week 12. Among these three bone substitutes, CO₃Ap (Cytrans) demonstrated the highest level of new bone formation. These results indicate the possibility that bone substitutes with compositions similar to that of bone may have properties similar to those of bone.