Formation of CaHPO4-2H2O in tooth enamel as an intermediate product in topical fluoride treatments.

Significant amounts of CaHPO4-2H2O (DCPD) were deposited in tooth enamel by pretreatment with a solution saturated with respect to DCPD. When these enamel samples were treated with a given fluoride solution, the fluoride uptake increased with increasing amounts of DCPD produced by the pretreatment. The interactions between enamel and acidic solutions to yield DCPD can be understood as dissolution-precipitation reactions and analyzed through the use of solubility phase diagrams.