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91	Efficacy and safety of various tooth-whitening products, with special reference to the three dimensional colour space (Lab) measurements and the microhardness tests Majeed, Abdul* January 2011 (has links) Philosophiae Doctor - PhD / Tooth-whitening or tooth-bleaching has become an integral part of modern dental practice. Today, a large number of whitening products are available on the market which are commonly categorized into dentist-supervised home bleaching, in-office bleaching and over-the-counter bleaching products according to their mode of application. This thesis looks into safety and efficacy of various tooth-whitening products and methods. / South Africa Tooth whitening Tooth bleaching Hydrogen peroxide Carbamide peroxide Sodium chlorite Microhardness Enamel Spectrophotometer Tooth colour CIE Lab* Clinical study Dentist-supervised home bleaching In-office bleaching Over-the-counter bleaching
92	Mechanisms Causing Ferric Staining in the Secondary Water System of Brigham City, Utah Wallace, Robert Derring 26 May 2007 (has links) Water from Mantua reservoir has, during some years, exhibited reddish-brown staining when used by Brigham City for irrigation. I propose that seasonal fluctuations in the reservoir chemistry create an environment conducive to dissolving iron from the iron-rich sediments, which subsequently precipitate during irrigation, resulting in a staining event. These conditions are produced by chemical and biological decomposition of organic matter, coupled with isolation of the hypolimnetic waters, which results in seasonal low concentrations of dissolved oxygen in these waters. Under these specific circumstances, anaerobic conditions develop creating a geochemical environment that causes iron and manganese reduction from Fe(III) to Fe(II) and Mn(IV) to Mn(II), respectively. These reducing conditions facilitate reduction-oxidation (redox) chemical reactions that convert insoluble forms of iron and manganese found in the reservoir sediments into more soluble forms. Consequently, relatively high amounts of dissolved iron and manganese are generated in the bottom waters immediately adjacent to the benthic sediments of the reservoir. Water withdrawn from a bottom intake pipe during these periods introduces iron-rich water into the distribution system. When this water is exposed to oxygen, reoxidation shifts redox equilibrium causing precipitation of soluble Fe(II) and Mn(III) back to highly insoluble Fe(III) and Mn(IV). The precipitant appears on contact surfaces as the aforementioned ferric stain. This research focuses specifically on the iron chemistry involved and evaluates this hypothesis using various measurements and models including field data collection, computer simulations, and bench-scale testing to validate the processes proposed. anaerobic hypolimnion epilimnion stratification iron-staining reddish-brown staining hypereutrophic mesolimnion dissolved oxygen benchscale models iron reduction manganese redox potential Mantua Reservoir dissolved iron precipitate reoxidation aerobic PHREEQC benthic sediments seasonal fluctuations iron-rich sediments calibration curve spectrophotometer ICP Beer's Law EPA Methods thermal stratification Civil and Environmental Engineering

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