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AFM observation of collapse and expansion of phosphoric acid-demineralized dentin.

The objective of this study is to provide additional data regarding morphological changes that occur to dentin matrices following demineralization with etchants. Our understanding of the mechanism of diffusion of comonomers into the demineralized substrate is very limited. It has been hypothesized that certain water-soluble polyelectrolytes (acidic proteins) and neutral proteins in dentin can influence the collapse of demineralized dentin when it is air dried. Some of these solubilized substances are thought to aggregate by the action of Ca cations, which become dissolved during H(3)PO(4) etching, ultimately resulting in some degree of collapse. In the current study, dentin surfaces were examined by atomic force microscopy (AFM) before and after treatment by 10% H(3)PO(4)containing increasing concentrations of CaHPO(4). Reversal of matrix collapse by aqueous 30% 2-hydroxyethyl methacrylate (HEMA) was evaluated by AMF for 60 min. The results demonstrate two forms of matrix collapse; we speculate that one form is induced by acidic noncollagenous polyelectrolytes and the other by neutral peptides. Our data indicate that further evaluation of the influence of endogenous noncollagenous proteins must be studied to understand the mechanism of the collapse and reexpansion dynamics of demineralized dentin networks.