Aims: The goal of this study was to investigate the phototoxicity of Photosan in combination with EDTA and a hand-held photopolymerizer used in dentistry for light-curing resins against leading key pathogens in caries, endodontic treatment failures, and periodontitis respectively. Methods and Results: Cellular uptake of Photosan was detected by fluorescence spectroscopy for Streptococcus mutans and Enterococcus faecalis but not for Aggregatibacter actinomycetemcomitans. Addition of 10% EDTA enabled the uptake of Photosan by A. actinomycetemcomitans. Killing of S. mutans and E. faecalis mediated by Photosan and blue light was concentration and light dose dependent, achieving a >= 99 center dot 9% (>= 3 log(10) reduction) efficacy of bacteria killing. In the presence of 10% EDTA, Photosan induced a reduction of >= 4 log(10) in the viability of A. actinomycetemcomitans at a concentration of 50 mu g ml-1, upon activation at a dose of 9 center dot 65 J cm-2 for 60 s. EDTA alone, light alone, and Photosan alone were not able to kill bacteria. Conclusions: Ten per cent EDTA and Photosan cause a potent phototoxicity against oral bacteria upon illumination with a photopolymerizer. Significance and Impact of the Study: Increasing antibiotic resistance and insufficient drug concentrations within the sulcus fluid are responsible for lacking antimicrobial efficacy. This study provides useful information that combination of Photosan, EDTA, and a photopolymerizer may be a potentially powerful tool for the efficient destroying of key oral bacteria.