The aim of the study was to evaluate the effects of Listerine(R), Meridol(R), and Perioaid(R) on the viability and total number of bacteria in established biofilms using an in vitro model under hydrodynamic conditions. Biofilms of Aggregatibacter actinomycetemcomitans were placed in a modified Robbins device and rinsed twice daily during 4 days. Bacteria were quantified by culture and quantitative polymerase chain reaction. Visualization of the samples was performed by scanning electron and confocal laser scanning microscopy, combined with a fluorescent vital staining. All three mouthrinses caused a significant reduction in the number of cultivable A. actinomycetemcomitans in a biofilm. Perioaid(R) was significantly the most powerful in killing the biofilm-protected bacteria and also in counteracting the development of thick dense microbial communities. The total amount of bacteria was not significantly affected by Listerine(R) and Meridol(R).