Objectives: The opacity of translucent teeth is very sensitive to surface roughness, because a roughened surface increase random reflection at the surface which increases the opacity. Therefore tooth transparency and surface roughness changes were monitored before and after in-office bleaching technique. Methods: The transparency parameters were recorded in the total light-permeation factor; TL, dispersed light permiation factor; DF, and parallel light permiation factor; PT. 20 extracted teeth of enamel and dentin were used. The teeth were sectioned longitudinally. Specimen of thickness (1.0mm) was measured with a turbidimeter at the measurement area with a diameter of 1mm. The differences in the transparency (TL, DF and PT) were determined using two-way ANOVA combined with Scheffe's test (P<0.05). Results: TL;0.643(0.121)-Enamel before bleaching, 0.593(0.126)-Enamel after bleaching,0.562(0.113)-Dentin before bleaching,0.499(0.112)-Dentin after bleaching, DF;0.595(0.115)-Enamel after bleaching, 0.547(0.119)-Enamel after bleaching,0.521(0.107)-Dentin before bleaching,0.463(0.108)-Dentin after bleaching, PT; 0.047(0.015)-Enamel before bleaching, 0.046(0.009)-Enamel after bleaching, 0.042(0.009)-Dentin before bleaching, 0.036(0.009)-Dentin after bleaching (Mean(SD), n=20, %). Significant differences were found in the transparency of TL, DF and PT among the samples of enamel and dentin, and between before and after bleaching treatment. The transparency (TL, DF and PT) of dentin was significantly lower than those of enamel. Conclusion: Bleaching reduced the transparency (TL and DF). Scanning electron microscope observation of bleached extracted teeth showed that prism enamel and dentin were decalcified and exhibited an increase in roughness after bleaching.

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