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The control of hydroxyapatite crystal initiation and growth during enamel development is thought to be mediated by the proteins of the extracellular matrix. However, the precise nature of these critical mineral−protein interactions remains obscure. In this study, fluid tapping mode atomic force microscopy was used to image, for the first time, the binding of extracellular proteins found in enamel matrix (amelogenin and albumin) to developing enamel crystals. Both albumin and amelogenin were found to be associated with the crystal surfaces under conditions close to physiological; however, the binding of the two proteins was distinctly different. Albumin appeared to bind as a monomer, whereas amelogenin was bound as aggregates resembling previously described “nanosphere” structures. Both proteins were arrayed on the crystal surface in a distinctive banding pattern, perpendicular to the c-axis. This pattern was coincident with recently identified positively charged domains on the crystal surface, suggesting ...

The adhesion force between two 11-amino-1-undecanethiol self-assembled monolayers has been measured as a function of pH in solutions of two ionic strengths, high (10-1 M) and low (10-4 M). In high ionic strength solutions, the force titration curve approximates to a sigmoidal step, centered at ca. pH 3, with negligible adhesion at low pH and a high adhesion (20 nN) at higher pH but with a previously unobserved drop in adhesion almost to zero above pH 12. In low ionic strength solutions, the shape of the force titration curve is radically different, comprising two peaks centered at ca. pH 6 and 10. The length of the alkyl spacer has a strong effect on the magnitude of the peak at pH 6 which increases significantly with decreasing spacer length, whereas the peak at pH 10 is unaffected. We propose that the pH 6 peak in low ionic strength conditions and the very high adhesion in high ionic strength buffer are due to a hydrophobic interaction between two disordered monolayers and that in-plane hydrogen bonding...

Dental fluorosis is an increasing problem, yet the precise mechanism by which fluoride exerts its effects remains obscure. In the present study, we have used atomic force microscopy to image and quantitate surface features of enamel crystals isolated from specific developmental stages of fluorotic and control rat incisors. The results showed a significant decrease in crystal surface roughness with development in control tissue. Crystals from fluorotic tissue were significantly rougher than controls at all stages of development, did not decrease in roughness during the later stages of their development and had many morphological abnormalities. These data clearly demonstrate an effect for fluoride on enamel crystal surfaces which could reflect changes in the nature and distribution of growth sites and/or in mineral–matrix interactions. These would be expected to affect crystal growth during maturation, resulting in the characteristic porous appearance of fluorotic lesions in mature teeth.

The present article describes the preparation and preliminary characterization of a novel phosphate-functionalized self-assembled monolayer (SAM) and the determination of the surface ionization states of the phosphate headgroup in aqueous solutions by chemical force microscopy (CFM). The phosphate headgroup used was PO(OH)2, a diprotic acid. The adhesion force between an AFM probe and a flat substrate, both of which were chemically modified with the same phosphate SAM, was also measured as a function of pH and ionic strength. At low ionic strength (10(-4) M), two peaks were observed in the force titration curve (adhesion force versus pH) at pH 4.5 and 8.4. The two peaks are positioned 2.4 and 1.2 pH units higher, respectively, than the acid dissociation constants obtained for the phosphate group free in aqueous solution. At high ionic strength (10(-1) M), the adhesion forces were reduced by 1 order of magnitude and the peaks were replaced by shoulders similar to those previously reported for acid force titrations. On the basis of JKR theory, the surface pKa values of the phosphate group in high ionic strength solutions were found to be 4.5 and 7.7, respectively. However, in light of the effects of ionic strength on the force titration curves, we discuss the applicability of JKR theory to nanoscopic measurements of adhesion force and surface pKa.

The chemical force titration behavior of carboxylic and phosphonic acid-functionalized tips and substrates has been found to be very strongly dependent on electrolyte concentration. Under low elect...