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.