Increased ash contents and estimation of dissolution from chemical changes due to in-vitro fluoride treatments

The in-vitro fluoride treatment technique has been introduced to investigate the composite behavior of bone tissue. Bone tissue with different mechanical properties can be obtained by varying the concentration, pH and immersion time in fluoride ion solutions. The chemical and physical changes in intact pieces of bone treated in-vitro with different concentrations of fluoride ions are studied. The amount of bone mineral that does not contribute to the mechanical behavior of bone tissue is estimated from the dissolution occurring in the fluoride treated bones. Cortical bones from 18-month-old steers were treated in-vitro with 0.145, 0.5 and 2.0 M sodium fluoride (NaF) solutions for three days. The dissolved bone mineral precipitates as calcium fluoride-like (CaF2/P with some phosphate [P] ions) and fluorapatite(FAp)/fluorhydroxyapatite(FHAp)-like materials within the bone tissue. The dissolution estimated from the presence of the precipitated fluoride phases is 5.6, 11.7, and 13.1% of the initial bone mineral content for the 0.145 M, 0.5 M, and 2.0 M NaF treatments respectively. Estimates of dissolution based on the measurements of phosphate and carbonate ions are lower and higher respectively when compared to the fluoride ion measurements. The wet and dry densities decreased slightly due to dissolution and re-precipitation while the ash content (ratio of the ash weight to dry weight) increased a small amount with increasing concentration of fluoride ion treatments. The increased ash content was due to the excess loss of water in the fluoride treated bones as compare to controls (untreated bone samples) during the drying process. The increased removal of water during the drying process may explain the increased ash contents in some in-vivo treatments.