Hydrogen Peroxide Tooth Bleaching Protocol

In this study, the bleaching agent containing 40% hydrogen peroxide was used according to the manufacturer’s recommendations (Opalescence Boost 40%, Ultradent Products Inc., USA). The product was brought to room temperature before mixing. Subsequently, the gel was placed on the labial surfaces of each sample with a thickness of 0.5–1.0 mm and applied for 20 min. The same procedure was repeated three times. Finally, the agent was washed away using copious distilled water. After this procedure, the samples were kept in distilled water until toothbrushing procedures.