Peroxide Bleaching Effect on Biaxial Strength/Modulus of Bovine Dentin

Objectives: This study evaluated the effects of carbamide and hydrogen peroxides on biaxial flexural strength and flexural modulus of bovine dentin.

Methods: Thirty coronal dentin discs (0.5 mm thick X 6.0 mm diameter) were prepared from bovine teeth. The dentin discs were randomly divided into three groups (n=10): control group (unbleached group); bleached with 10% carbamide peroxide for 8 hours; bleached with 38% hydrogen peroxide (the gel was applied 3 times consecutively for 15 minutes each application). The dentin discs were stored in 100% humidity during the bleaching or not. The specimens were tested in a biaxial flexural apparatus held in a universal testing machine (Instron 5844) at 1.27 mm/min until failure occurred, and biaxial mechanical properties were calculated. Within a given test parameter, data were statistically analyzed by ANOVA and Fisher`s PLSD test (pre-determined alpha = 0.05).

Results:

Table presents mean (SD) of test parameter results (MPa) among treatment groups.

TEST PARAMETER	Control group (unbleached)	10% carbamide peroxide	38% hydrogen peroxide
Flexural Strength	188 (45) A	170 (53) AB	138 (51) B
Flexural Modulus	8969(966) a	8987 (1251) a	6848 (1155) b

Within a test parameter, values having similar letters are not significantly different.

The 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group (p=0.0309) Hydrogen peroxide treatment resulted in significantly lower flexural modulus, when compared to control group and carbamide peroxide bleaching (p=0.0002).

Conclusions: Exposure of bovine dentin to hydrogen peroxide significantly reduces both flexural strength and modulus compared to no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.