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Objective:The clinical application of cold light-bleaching technique is growing during these years.This technique is based upon whitening formula(30% Hydrogen Peroxide mainly) activated by certain wavelength intensity blue light, in order to restore the color of discolored teeth .Although previous studies have indicated that 30 % Hydrogen Peroxide induced slight demineralization on the surface of enemal ,there are only some reports about evaluating the effects of cold light tooth whitening technique ,but no information is available about further research on the relative effects of configeration ,component of dental enamel .The purpose of this study is to investigate the effct of cold-light treatment on surface configeration, component, roughtness of dental enamel,by observing the changes of surface configeration,mineral components, physical character of extracted teeth,and to evaluate the effects and safety of cold light tooth whitening kit on bleaching teeth . scanning electron microscope(SEM), electron spectroscopy SRD, microhardness tester were used in this study .Method: Twenty freshly extracted teeth are distributed randomly into tow groups( A group for conventional procedure ; B group for time-prolonging procedure ,ten teeth in each group ). All the teeth were splited buccolingually into two parts, mesiobuccal parts were in testing group A1,B1, distal parts were in controling group,forty specimens in all.Teeth in group A covered by whitening formula are exposed by cold light for eight minutes, three times in all.Twelve minutes for group B also three times in all.All the specimens are examined with Scanning electron microscopy,500 times and 2000 times with ,and tested the microhardness of dental enamel surface simultaneously.All the data were analyed
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