Adsorption of dentine proteins onto spheroidal calcium phosphate in a neutral and in an acidic environment.

The adsorption of four different dentine protein fractions onto hydroxyapatite (HAP) was investigated in a nearly neutral (pH 6.7) and in an acidic environment (pH 5.0). The soluble dentine proteins were isolated according to their extractability in successively: 4M guanidine-HCl (GuHCl), 0.5M acetic acid pH 3 (after extraction with GuHCl), and 0.01M EDTA pH 7.4 and 0.1M EDTA pH 7.4 (after complete demineralization with acetic acid). The amounts isolated were 1.2, 3.3, 6.1 and 3.7 mg protein per gram dentine, respectively. The GuHCl extractable proteins exhibited the lowest affinity and the acetic acid extractable proteins the highest affinity for HAP. Acetic acid extractable proteins, were significantly less adsorbed than the other protein fractions at pH 5.0. The maximum adsorbed amount of these proteins increased with decreasing pH which indicated that all the soluble dentine proteins, except perhaps those that one GuHCl-extractable have to be considered as potential demineralization inhibitors.