Objective: To evaluate the effect of 10% carbamide peroxide (CP) on primary tooth enamel by measuring the calcium loss, surface microhardness and morphology. Methods: Extracted human primary anterior teeth (10/group; 3 groups) were sectioned longitudinally at the middle, with one section treated with 10% CP and the other with deionized water (control). Each sample was covered with sticky wax except a 3 x 3 mm window on the labial surface. The treatment was 6 hr/day for 1, 7 or 14 days. Calcium concentration of the test media was determined using an atomic absorption (AA) spectrophotometer. Enamel surface Knoop microhardness (KHN) was determined with a microhardness tester. Scanning electron microscopic (SEM) evaluation was performed at 12X, 100X, 2,000X and 4,000X on representative samples to examine the effect of treatments on surface morphology of primary enamel. Two-factor ANOVA was used to analyze the data obtained from the AA and KHN experiments, while the SEM results were descriptive. Results: Samples treated with 10% CP were found to have a significant increase (p<0.001) in the calcium loss with the exposure time (0.219, 0.438 and 0.542 mcg/mm2 at 1, 7 and 14 days, respectively), which were significantly higher (p<0.05) than that for the control at each time point (0.176, 0.175 and 0.189 mcg/mm2 at 1, 7 and 14 days, respectively). The KHN data were comparable within and between the experimental (245.4, 234.3 and 246.4 at 1, 7 and 14 days, respectively) and control (248.8, 250.3 and 258.3 at 1, 7 and 14 days, respectively) groups. SEM results were similar at 100X, although mild surface morphology changes were detected at 2,000X. Conclusions: The exposure of primary tooth enamel to 10% CP up to 14 days at 6 hr/day causes calcium loss but does not adversely affect its surface microhardness or significantly alters the surface morphology.

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