EFFECTS OF STRONTIUM IONS ON GROWTH AND DISSOLUTION OF HYDROXYAPATITEAND ON BONE-MINERAL DETECTION

Preparation and analyses of a series of hydroxyapatites (HA) containin g 1-10 mol % of Ca2+ replaced by Sr2+ is reported. The solubility of t hese apatites is found to increase with increasing content of Sr2+. 10 % SrHA dissolves faster than CaHA at given values of Ca2+ and phosphat e concentrations, but with a similar rate at the same degree of satura tion. Sr2+ is found to inhibit the rates of both dissolution and growt h of CaHA and 10% SrHA. at pH 7.2, CaHA being more strongly inhibited by Sr2+ than 10% SrHA. The effect of partial substitution of Ca2+ in h ydroxyapatite by Sr2+ on bone mineral content (BMC) and bone mineral d ensity (BMD) measured by dual energy X-ray absorptiometry has been stu died using three commercial densitometers. Extrapolating the absorptio n data for up to 10% replacement of Ca2+ by Sr2+ to 100% substitution of Ca2+ by Sr2+ in HA leads to an apparent increase in BMC or BMD of a bout a factor of 10. This factor is in agreement with theoretical calc ulations using attenuation coefficients of the atoms concerned. It is concluded that existing BMC scanners register artificially high values of BMC if the bone contains significant amounts of Sr2+ or other meta l ions with atomic number larger than calcium. (C) 1997 by Elsevier Sc ience Inc.