AbstractThe aim of this study was to determine whether the use of a pre‐brushing mouthwash Plax ‐ reduced extrinsic tooth stainingin vivoandin vitro.Firstly, in a double‐blind placebo controlled cross‐over study, 20 subjects with tooth staining used Plax® or a placebo for 14‐day periods separated by a 1‐month wash‐out period. The area of stain was assessed before and after each mouthwash had been used from clinical photographs. Secondly, extracted 3rd molar teeth were stained with tea and chlorhexidine. After exposure to either Plax® or placebo, the teeth were brushed in a standardized manner. The area and intensity of stain were assessed before and after rinsing and brushing. Results of the studyin vivoshowed that the mean % stained area for any of the surfaces studied changed very little throughout the study. No statistically significant changes were detected (Studentt‐test,p>0.05). Results of the studyin vitroshowed that the mean area of stain fell by 19% after exposure to Plax® and by 17% after exposure to placebo. No statistically significant changes were detected (Studentt‐test,p>0.05). There were also no significant changes in intensity (Wilcoxon signed