Could chlorhexidine be an adequate positive control for antimicrobial photodynamic therapy in- in vitro studies?

•Chlorhexidine (CHX) diluted in a neutralizer did not present substantivity.•CHX + neutralizer and aPDT presented similar antimicrobial immediate effects.•It is advocate the use of CHX + neutralizer as a positive control to aPDT. Background: Chlorhexidine digluconate (CHX) is commonly applied as positive control of new antimicrobials, because it is considered the gold-standard for chemical plaque control. The aim of this study was to compare the effect of treatments with curcumin-mediated aPDT and CHX in relation to the viability of specific microorganism groups in two distinct times (immediately and 24 h later). Methods: Dentin caries microcosms were grown on bovine dentin discs (37 °C, anaerobiosis) for 3 days in the Active Attachment Amsterdam Biofilm Model. The biofilms were treated with 300 μM curcumin and 75 J.cm−² LED, or 0.06% and 0.12% CHX. Then, total microorganisms, total streptococci, mutans streptococci, and total lactobacilli counts were determined. The statistical analysis was conducted by Kruskal-Wallis and post-hoc Dunn's tests (P