The growth rate of the hydroxyapatite (0001) face in pseudophysiological solution was measured directly for the first time by Moire phase shift interferometry. Common-path-type interferometry and a newly developed signal processor used for the phase shift technique enabled the precise and stable measurement of growth rates. It was determined that the growth rate was strongly time-dependent. The growth rate gradually decreased with time and finally ceased although the concentration of the solution remained constant. The thickness of the layer grown on the seed crystal was about 500−700 nm, while the growth rate during initial growth stages was of the order of 10-2 nm/s. respectively. Detailed surface morphology was observed by atomic force microscopy (AFM), indicating that the growth mode was multiple two-dimensional nucleation.

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The osteoporosis model had a lower BMD than the control group in the region closest to the implant during an important time for osseointegration. This result suggests that senile osteoporosis might be a risk factor in implant therapy. However, the osteoporosis model and the control group had no difference in peri-implant BMD in the cortical bone region. This suggests that risk might be avoided by implant placement that effectively uses the cortical bone.

Single-crystal hydroxyapatite and OH-carbonated hydroxyapatite have bending strength much higher than that of dense hydroxyapatite ceramic, indicating potential applicability to a load-bearing biomaterial. However, the effects of carbonate on the strength are less clear. The objective of the present study was to determine the bending strength and Young's modulus of these single crystals with carbonate contents from 0 to 0.62 in CO2 wt%. Three-point bending tests were performed by means of a modified ultra-microhardness tester with a span of 380 microm and a bending direction <210> of the single crystals. The crystals were broken in air, water, and air after immersion in a cell culture medium for 3 wks. The average Young's modulus of the single crystals was from 54 to 79 GPa. The average bending strength of the single crystals in air was 500+/-184, 468+/-205, 513+/-151, and 450+/-162 MPa for those with 0, 0.09, 0.37, and 0.62 wt% carbonate, respectively. No significant decrease in strength was found for hydroxyapatite single crystals both in water and after the immersion in the medium. However, the strength of OH-carbonated hydroxyapatite single crystals decreased significantly by 23 to 43% in water in proportion to the carbonate content. The strength of single crystals with 0.37 and 0.62 wt% carbonate decreased significantly, even after the immersion in the medium. Therefore, hydroxyapatite single crystals are superior to OH-carbonated hydroxyapatite single crystals as a biomaterial for a load-bearing purpose.