Papers by Author: Ulrich Bismayer

Abstract: The surface crystal chemistry of enamel treated with peroxide-based (the commercial product Opalescence Xtra Boost as well as aqueous solutions of H2O2) and citric-acid-containing bleaching agents (the commercial product Rapid White as well as aqueous solutions of C6H8O7) were studied by Attenuated Total Reflectance Infrared Spectroscopy and electron-probe microanalysis. The results show that the treatment with H2O2-based reagents leads to no side effects on the enamel superficial layer, whereas C6H8O7-based agents deteriorate the enamel mineral component. Hence, bleaching with citric-acid-containing products cannot be recommended.

Abstract: The effect of two bleaching materials on dental enamel was studied by vibrational spectroscopy. Human molar enamel sections parallel to the dentin-enamel junction were one-side polished and treated with bleaching agents containing 38% hydrogen peroxide (Opalescence Xtra Boost) or 20% carbamide peroxide (Opalescence PF 20%). Then the crystalline structure and molecular inclusions of the bleached samples were analyzed by Raman scattering and attenuated total reflectance infrared spectroscopy. No spectral difference was observed between the unbleached enamel and that bleached with the two different agents, which indicates no significant occurrence of structural or chemical changes in enamel apatite due to bleaching.

Abstract: A considerable fraction of atoms in nanosize particles is at the grain surface (due to the small size of the crystals). We assume that the surface atoms form a separate structural phase relative to the bulk of the grain (the core). Therefore, one set of the lattice parameters characterizing a nanocrystal may be inadequate for a unique description of its structure. An alternative evaluation of diffraction data of nanocparticles, based on the 'apparent lattice parameter' is proposed. Based on this new methodology it is shown that real nano-crystals constitiute a complex, more than a one-uniform-phase structure.