Objective: to determine the effects of 10% Carbamide Peroxide (CP) bleach agent on surface and sub-surface properties of dentin using SEM. Methods: rectangular dentin specimens (2x2x20 mm) were sectioned from extracted bovine teeth. Specimens were randomly divided into 4 treatments and 4 parallel control groups (n = 8 / group). All treatment groups were immersed in 10% CP for 6 h /day for 2 w, while control groups were stored in distilled water. Following the bleach treatment groups 2 & 3 were further immersed for 2 w in fluoride and artificial saliva, respectively. Group 4 specimens were bleached as whole teeth, and then sectioned to observe changes in sub-surface dentin. Randomly selected specimens from each group (n = 3) were critical-point dried and coated with palladium to examine under SEM. Directly treated dentin surfaces as well as sub-treated surfaces were examined for changes. Results: SEM photographs of 10% CP-treated specimens showed loss of the smear layer and more exposed dentinal tubules in comparison to the control group. Specimens in distilled water had more intact smear layer with little or no tubules exposed. Specimens exposed to either fluoride or artificial saliva following bleaching treatment showed a precipitate on the dentin surface in comparison to control group. Fluoride treatment and artificial saliva storage did not reverse the changes that were associated with bleaching treatment. In contrast changes in dentin surface morphology were not evident in either treated or control whole tooth specimens. Conclusions: sectioned specimens bleached with 10% CP showed evidence of changes in dentin surface appearance. However, whole teeth dentin specimens did not show morphological surface changes when subjected to same CP treatment under conditions of this study. Supported by American Academy of Esthetic Dentistry grant.

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