the effect of mouthwash containing chitosan/zinc oxide nanoparticles on surface hardness and color change of bleached enamel

Introduction: this study compared the effects of mouthwashes containing chitosan/zinc oxide nanoparticles, 0.2% chlorhexidine, 1.5% hydrogen peroxide (colgate), and distilled water on the color and microhardness of bleached enamel. materials and methods: sixty bovine incisors were randomly divided into four groups (n = 15). after polishing and tea staining for six days, baseline color and microhardness were recorded using the cielab system and vickers test. the enamel surfaces were bleached three times with 40% hydrogen peroxide. after ten days, measurements were repeated. the bleached samples were then immersed in 5 ml of each mouthwash twice daily for 14 days. the synthetic mouthwash contained 1% chitosan and 500 µg/ml zinc oxide nanoparticles. color and microhardness were re-evaluated, and data were analyzed using the kruskal–wallis and post-hoc tests (α = 0.05). results: significant color differences were observed between the mouthwash groups and water (p < 0.05), with no significant difference between chlorhexidine and the nanoparticle mouthwash. both the nanoparticle and colgate mouthwashes similarly increased enamel microhardness, while chlorhexidine caused a slight decrease.conclusion: mouthwash containing chitosan and zinc oxide nanoparticles improved bleached enamel microhardness without affecting color stability compared to 0.2% chlorhexidine. keywords: chitosan; mouthwashes; nanoparticles; tooth bleaching; zinc oxide; enamel; remineralization.