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Objectives: The purpose of this study was to determine if enamel that had been bleached by hydrogen peroxide gel (HPG) was at increased risk of demineralisation than un-bleached enamel. Methods: Human incisors/canines were selected, roots sectioned and the enamel gently pumiced. Each enamel specimen was mounted into acrylic, covered with varnish save for an exposed window, and then randomly assigned to one of 4 groups; a) 10% HPG, b) 15% HPG, c) 20% HPG and d) 10% Urea Peroxide Gel. Each specimen was moistened with saliva and the appropriate formulation placed for 2 hours. The teeth were then rinsed and gently brushed for 2 minutes in an automatic tooth-brushing machine. This procedure was repeated for 20 cycles for a total of 40 hours of exposure. In order to ensure that bleaching had taken place, tooth shades were monitored using digital photographs and the Shade-Eye device. Following the bleaching process, the varnish was removed from the enamel and refreshed leaving a window exposing both bleached and non-bleached enamel. Each specimen was then subjected to a total of 10 days of cariogenic challenge (2.2 mM KH2PO4, 50 mM acetic acid, 2.2 mM of 1 M CaCl2, 0.5 ppm fluoride at pH 4.5) with gentle agitation at 37oC. After each 24 hours of exposure each sample was examined using QLF. Results: Colour change was detected in all teeth. Demineralisation was detected in all samples (Delta Q 89±18.9), in both bleached and non-bleached areas. There was no statistical difference detected between the bleached and non-bleached areas either within the treatment groups or between them (p<0.05) Conclusions: Bleaching of teeth by HPG in vitro does not appear to increase the susceptibility of enamel to acid demineralisation at the concentrations and durations employed within this study. suehigh@liv.ac.uk |