Effect of Stannous and Fluoride Ions on the Rate of Crystal Growth of Hydroxyapatite

Stannous and fluoride ions affected the rate of crystal growth of calcium phosphate from stable, supersaturated solutions inoculated with pure synthetic hydroxyapatite seed. Stannous ions appeared to inhibit the growth by a simple adsorption process; the effect of fluoride ions was much more difficult to in-terpret. The advantages of using the technique of seeded growth from stable supersaturated solution to study the crystal growth of hy-droxyapatite (Cal0 (P04)6 (OH)2, here-after written HAP) has been discussed pre-viously. ' This technique is particularly applicable to the study of the influence of additives, since their effect on the crystal growth process can be investigated with minimal complications caused by nucleation. In spontaneous precipitation, nucleation and growth occur simultaneously2 and any ap-parent additive effect cannot be ascribed with certainty to either nucleation or growth. In contrast to results from "homogeneous" nucleation studies, the experimental results obtained for seeded growth are highly re-producible and therefore small effects caused by additives can be discerned easily. It is becoming more apparent that a large number of desirable and undesirable mineral-ization processes that occur in biologic systems are initiated by heterogeneous nucleation.3'4 Another related phenomenon thought to be important in regulating bio-logic calcification is a mechanism5 in which deposition of the mineral phase is retarded by a natural inhibitor, possibly pyrophos-phate, which is always present in the vita