Bleach Essay

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2.4.1 Peroxide based Bleaching Agents
These products usually contains hydrogen peroxide or one of its precursors as an oxidizing agent
a. Hydrogen peroxide (HP,H2O2) is an effective bleaching agent. It is a pale blue liquid and is slightly more viscous than water. The molar mass of hydrogen peroxide is 34.0147g/mol .As the molecular weight of hydrogen peroxide is low it can penetrate dentin and break the bond of organic and inorganic compound inside the dentinal tubules[36] .The photolysis of hydrogen peroxide can only be achieved by low frequency light of wavelength 365nm or less and heat[37, 38].

b. Sodium perborate (NaBO3) is odorless, white, water soluble powder. It is safest and most easily controlled material for bleaching when prepared with distilled water or hydrogen peroxide. It is stable in dry state but it breaks down to form sodium metaborate, nascent oxygen and hydrogen peroxide in presence of water, acid and warm air[2].Sodium perborate may be monohydrate ,trihydrate and tetrahydrate and are mostly used for intracoronal bleaching[39].

c. Carbamide peroxide (CH6N2O3 or CH4N2O•H2O2, CP), is a white crystalline solid which dissociates into hydrogen peroxide and urea upon contact with water .It is also called urea peroxide. Urea again dissociates into ammonia and carbon dioxide. The release of ammonia and carbon dioxide elevates the pH value of the bleaching agent in the oral cavity during the bleaching process. For bleaching purpose 10-35% of carbamide peroxide is used. Usually 10% carbamide peroxide produces 3-3.35% hydrogen peroxide.

2.4.2 Non Peroxide based Bleaching Agents
These materials are based on sodium chlorite (NaClO2) which are activated by citric acid. Sodium chlorite is an very good oxidizing agent wh...

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...mperature stable and visible light active oxygen rich anatase phase titanium dioxide[77].In this method hydrogen peroxide was added to amorphous titanium dioxide to form peroxo titania complex. The band gap of the resulting titania decreased as the molar ratio of the hydrogen peroxide was increased (figure 5). The band gap narrowing was identified as factor responsible for the visible light activity. The hydrogen peroxide modified samples were more photoactive and thermally stable.

Arti bandgar et.al. in 2012 used aqueous peroxo titanate complex (PTC) precursor to obtain pure titanium dioxide[81] .Several characterization were done such as DSC–TGA, XRD, UV–Vis, SEM and TEM. In the study reflux time of PTC has increase and crystalline size too. The surface morphology of TiO2 changed to rice like shape and furtherin ellipsoid rods like shape from hexagonal shape.
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