According to Essentials of Dental Caries, the antimicrobial agent of the mouthwash or mouth rinse cannot diffuse into the bacterial biofilm. Therefore, any effect of the mouthwash will remain limited to the superficial layers (Kidd, Edwina. Essentials of Dental Caries: The Disease and Its Management, 3rd Ed.: The Disease and Its Management. United Kingdom, OUP Oxford, 2005.)