Phosphoprotein modulation of apatite crystallization.

Several phosphoprotein preparations (phosvitin, rat incisor and fetal calf molar dentin phosphoproteins) all inhibit apatite growth/replication from pre-existing crystal seeds in metastable solutions. Two stages of the crystal growth process were inhibited by these phosphoproteins. First, an initial lag period was induced, probably associated with seed surface phenomena. This period was prolonged indefinitely when a combination of phosphoprotein precoated seeds was used together with soluble phosphoproteins in the crystal growth reaction. Second, the phosphoproteins prolonged that stage of the reaction where octacalcium phosphate is the predominant mineral phase present prior to its conversion to the final apatite product. Pretreatment of the phosphoproteins with calcium diminished their inhibitory activity to seeded crystal growth as well as towards de novo apatite formation in synthetic extracellular fluids. The presence of collagen diminished the inhibitory activity of the phosphoproteins towards de novo precipitation but had no effect on phosphoprotein-modulated apatite crystal growth in the seeded systems. These results suggest a potential regulatory role for phosphoproteins in dentin mineralization.