The Constant Composition (CC) method has been used to study the dissol
ution kinetics of whole powdered human dentin as a function of calcium
phosphate concentration at relative undersaturations with respect to
hydroxyapatite (sigma(HAP)), ranging from +0.8 to -2.8, ionic strength
from 0.05 to 0.30 mol/L(1) in sodium chloride or potassium nitrate, p
H 4.00 to 5.50, and molar calcium/phosphate ratio in the reaction solu
tions from 0.05 to 11.1. The results suggest that human dentin behaves
as a mixture of at least two calcium phosphate phases, HAP-Like and o
ctacalcium phosphate-like, OCP-like. Significant dissolution took plac
e in solutions that were even supersaturated with respect to HAP, and
the rates exhibited a striking insensitivity to relative undersaturati
on, while influenced by ionic strength, pH, and molar calcium/phosphat
e ratio in the reaction solutions. Although the dissolution was retard
ed in the presence of magnesium ion, the reaction rate showed the same
insensitivity to undersaturation with respect to calcium phosphate.