Morphological and chemical characterization of tooth enamel exposed to alkaline agents.

OBJECTIVES: In this study, morphological and chemical changes in teeth enamel exposed to alkaline agents, with or without surfactants, have been investigated. In addition, chemical effects of the organic surface layer, i.e. plaque and pellicle, were also investigated. METHODS: The present study was conducted using several techniques: Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS: From XPS-measurements, it was found that exposure to alkaline solutions resulted in a massive removal of carbon from the tooth surface, and that the addition of surfactants increased the rate under present conditions. Based on the results from the FTIR-analysis, no substitution reactions between phosphate, carbonate and hydroxide ions in the enamel apatite could be detected. From a minor SEM-analysis, degradation and loss of substance of the enamel surface was found for the exposed samples. From XRD-analysis, no changes in crystallinity of the enamel apatite could be found between the samples. CONCLUSIONS: The findings in this study show that exposure to alkaline solutions results in a degradation of enamel surfaces very dissimilar from acidic erosion. No significant erosion or chemical substitution of the apatite crystals themselves could be discerned. However, significant loss of organic carbon at the enamel surface was found in all exposed samples. The degradation of the protective organic layer at the enamel surface may profoundly increase the risk for caries and dental erosion from acidic foods and beverages.

XPS at solid-aqueous solution interface.

Application of X-ray Photoelectron Spectroscopy (XPS) to study the solid-aqueous solution interface is reviewed. XPS provides complementary physicochemical information about electrical double layer from the perspective of the solid surface. Experimental techniques, such as differential pumping, controlled adsorption/co-adsorption, freeze-drying, and fast-freezing, are discussed for both electrochemical and dielectric solid-solution interfaces. The use of fast-freezing, as applied to wet pastes centrifuged from aqueous suspensions, makes it possible to approach a real solid-solution interface in UHV conditions. XPS data allow estimation of the surface density of counter-ions, surface point of zero charge, and in some cases the measurement of surface potential. Interfacial chemical reactions such as ion pair formation, specific adsorption and ligand exchange can be directly observed. The technique is easy to apply to any suspension including colloids and gels of inorganic or organic nature, and can be adapted for electrochemistry as complementary to traditional "emersed electrode" studies.