The purpose of this in situ study will be to evaluate the influence of staining solutions (coffee and soda cola) used during the tooth bleaching with high or low concentrations of hydrogen peroxide agents. One hundred and forty enamel blocks will be obtained from bovine teeth. Five blocks will be used for micromorphology surface evaluation. The other 135 enamel blocks will be randomly positioned in intraoral devices (9 blocks per devices) that will be used for 15 volunteers during for 15 days. During this time, bleaching treatments will be performed in different enamel blocks with: high concentration of hydrogen peroxide (Opalescence Boost PF 40%/ Ultradent) for 40 minutes in 3 sessions (1º, 8º and 15º days of treatment), low concentration of carbamide peroxide (Opalescence PF 10%/ Ultradent) for 60 minutes daily during 15 days; control, no bleaching agent will be applied. The enamel blocks will be immersed in staining solutions (coffee or soda cola) daily for 30 minutes for 15 days within a factorial design of bleaching treatment x staining solutions 3 x 3 (n=15). The analyses of color with spectrophotometer (VITA Easyshade® Advance, Vita), roughness (Suftest SJ-210, Mitutoyo) with static load of 5N and speed 0.05mm/s, Knoop microhardness (Pantec HVS 1000, Panambra) with static load of 25g/s and surface micromorphology (JSM 5900LV, JEOL Ltda) with increase 500 a 2000 times will be made before and after bleaching treatments associated with immersions in staining solutions. For the all study variables the data will be inserted in a digital spreadsheet, applying parametric or non-parametric tests. The level of significance will be 5%. The surface micromorphology analysis will be assessed qualitatively regarding the presence of erosions and porosity.
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