. 2020 Jan 10;45(1):e12. doi: 10.5395/rde.2020.45.e12

Table 2. Mean values of Knoop microhardness before and after bleaching with carbamide peroxide, hydrogen peroxide, and distilled water (control) for all materials used.

Materials	Before bleaching	After bleaching with 16% carbamide peroxide	After bleaching with 35% hydrogen peroxide	Control
Opallis	83.5 ± 4.5^b	80.4 ± 6.6^b	80.5 ± 4.9^b	91.2 ± 4.3^a
Opallis + BisCover	24.5 ± 2.5^b	25.4 ± 2.6^b	25.6 ± 2.3^b	28.1 ± 0.8^a
Supreme XT	92.9 ± 4.1^a	93.1 ± 2.2^a	93.0 ± 1.5^a	95.0 ± 7.6^a
Supreme XT + BisCover	28.1 ± 2.9^a	28.4 ± 1.7^a	29.5 ± 3.8^a	28.4 ± 2.3^a
Enamel	423.9 ± 30.5^a	200.0 ± 23.8^b	163.6 ± 54.9^b	398.6 ± 0.0^a

Data shown are mean ± standard deviation.

^a,bLowercase superscripts indicate statistically significant differences (p < 0.05) between values in the same row.