Effect of direct peroxide bleach application to bovine dentin on flexural strength and modulus in vitro

Objectives. The objective of this study was to determine the effects of carbamide peroxide (CP) and hydrogen peroxide (HP) bleaching on the flexural strength (FS) and flexural modulus (FM) of dentin. Methods. 2×2×20 mm bovine dentin specimens were immersed in the bleaching agents to simulate overnight (10 or 15% CP, 6 h daily, 2 weeks), exaggerated overnight (10% CP, 6 h/day, 5 days/week, 2 months), daytime (6.5 or 7.5% HP, 1 h daily, 3 weeks) and in-office (35% HP, 1 h/day, 2 days/week, 3 weeks) treatment protocols. Distilled water (DW) and a placebo gel acted as control immersion materials. After immersion, the specimens were rinsed and stored in DW. Mechanical testing was performed 24 h after the last treatment using an Instron Universal Testing Machine with a crosshead speed of 0.75 mm/min. The results were analyzed by ANOVA and Tukeyʹs tests (p<0.05). Results. There were significant reductions in the FS and FM of dentin after 2-week and 2-month exposures to CP. There were no significant differences in the FS or the FM of the dentin among the HP treatment and control groups. Conclusions. Direct in vitro application of CP bleaches caused significant decreases in dentin FS and FM. Similar decreases were not observed among the HP-treated dentin groups, which were exposed to shorter treatment times. Further research is needed to determine the effect of CP and HP on dentin in vivo.