Abstract: To observe the influence of fluoride on the permeability and the bleaching effect of such bleach as Carbamide peroxide; to evaluate whether the use of 2 percent sodium fluoride before bleaching would decrease bleaching efficacy of HPCP when compared with a placebo and to confirm the applicability and reliability of the fluoride in clinic. Methods The crowns of 36 caries and developmental defect free human maxillary incisors were stained internally with a standard tea solution and colorimetric analysis was done with VITA shade guide. 12 specimens were bleached with light activated 35% hydrogen peroxide and another 12 were bleached by the same agents after using 2%NaF. 12 others were placed in ionized water (control group). The exposure time was all 30 mins. Vita shade guide [SG] was employed before, after tea staining and after power bleaching/water treatments. Eighteen specimens from three groups were sectioned mesio-distally. An additional 18 specimens from the bleach and the control group were sectioned labio-palatally. The stain area for each specimen was measured and compared with image analysis software. Results There was no significant difference in the change of color gradation after bleaching between two groups and there was no significant difference in bleaching depth of dentine between the bleaching group and NaF bleaching group. With tea staining, the mean changes in Vita shade guide units (SGU) ranged from 3.66 to 8.33. Samples bleached and sectioned mesio-distally showed stain coverage of 28.6– 39.4%, while palatal sections showed stain coverage of 58–72%. Control samples, whether sectioned mesio-distally or labio-palatally, showed staining throughout the dentine (97–100% coverage).Conclusion The use of fluoride partly before bleaching does not have influence on bleaching effect or depth.

Key words: Sodium fluoride, Tooth bleaching, Shade guide unit, stain coverage