The seeded growth of calcium phosphates. The kinetics of growth of dicalcium phosphate dihydrate on enamel, dentin, and calculus.

The kinetics of growth of calcium phosphates on synthetic hydroxyapatite (HAP), human enamel, whole dentin, and human calculus has been studied at 37 C at pH values from 4.97 to 5.10 held constant by the pH-stat addition of base. Following an initial induction period, dicalcium phosphate dihydrate (DCPD) crystallization takes place on the surface of these solids in all cases, even though the solutions are highly supersaturated with respect to HAP. The second order crystal growth kinetics are characteristic of the crystallization of DCPD on pure DCPD seed material. The ability of the substrate surfaces to nucleate DCPD falls in the order, synthetic HAP greater than enamel greater than calculus greater than dentin. Nucleation of DCPD, which is completed during the initial induction period, is very sensitive to small changes in pH, from 4.99 to 5.10.