The growth of calcium phosphates on hydroxyapatite crystals. The effect of fluoride and phosphonate.

The nature of the calcium phosphate phase which precipitates on hydroxyapatite seed crystals can be controlled by varying the HAP seed concentration. At low seed concentrations, dicalcium phosphate dihydrate (DCPD) is formed while at high seed levels a more basic phase precipitates. It has been found that fluoride ion increases the percentage of basic phase that crystallizes while ethylidenediphosphonic acid encourages the formation of DCPD. This behavior is explained by the competition between the nucleation of DCPD and the crystal growth on sites already present on the HAP seeds.