Protein and mineral changes in bovine enamel during in-vitro demineralization

Mineral distributions with and without a softened surface layer were studied. The molar Ca:P ratio of released material was due to preferential Ca-loss significantly higher from surface-softened enamel than from lesions. The molecular weight (less than 1800) distributions of released proteinaceous matter were similar. The protein release during surface softening contained more large peptides, whereas its amino-acid composition was more acidic amino acids compared with lesion formation. The protein content of released material during demineralization, acetic acid-soluble protein (at pH 4.5) and total protein of sound enamel showed that (i) enamel proteins were partially soluble in an acetic acid-buffer under mild acidic conditions and (ii) enamel proteins soluble in acetic acid-solution were partially released during demineralization. It is postulated that during enamel demineralization the dissolution of acid-soluble proteinaceous matter and its partial adsorption on newly-created sites of partially-dissolved crystals may explain the partial release of acid-soluble proteins. In case of lesion formation on the other hand new adsorption sites on new crystal surfaces formed in the surface layer are formed as well, which may account for the differences in mol.wt distribution and amino-acid composition.