This in vitro study aimed to evaluate the effect of nonthermal atmospheric pressure plasma (NAPP)-activated hydrogen peroxide (HP) and deionized water (DW) on enamel microhardness and enamel surface morphology.

This in vitro study aimed to evaluate the bleaching efficacy and color stability of nonthermal atmospheric pressure plasma (NAPP)-activated 40% hydrogen peroxide (HP) and deionized water (DW). Methods: Two hundred-forty bovine enamel−dentin samples were stained with a coffee solution before bleaching. Samples were randomly divided into 12 (n = 20): (1) HP for 5 minute (HP-5), (2) HP-10, (3) HP-20, (4) Plasma-HP-5, (5) P-HP-10, (6) P-HP-5/HP-15, (7) P-HP-10/HP-10, (8) P-DW-5, (9) P-DW-10, (10) DW-5, (11) DW-10, and (12) DW-20. After bleaching, the samples were re-stained for 48 h using red wine. The color differences measured using a dental spectrophotometer after bleaching and after re-staining were reported as ΔE1 and ΔE2, respectively. The data were analyzed using Kruskal−Wallis and Mann−Whitney U tests (p< 0.05).