Journal of Dental Research, Vol 77, 1560-1568, Copyright © 1998 by International & American Associations for Dental Research Online Journals
Mechanical properties of hydroxyapatite and OH-carbonated hydroxyapatite single crystals
K. Teraoka, A. Ito, K. Maekawa, K. Onuma, T. Tateishi and S. Tsutsumi
Institute of Earth Science, School of Education, Waseda University, Ibaraki, Japan.
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.
