The antimicrobial effectiveness of photodynamic therapy used as an addition to the conventional endodontic re-treatment: A clinical study

•The addition of the aPDT to the conventional chemomechanical root canal preparation led to the significant further reduction of the number of CFUs or even to complete elimination of bacteria in some cases.•The addition of the aPDT to the conventional chemomechanical root canal preparation led to the significant of bacteria species from the root canal.•The combination of chemomechanical preparation and the aPDT was more successful elimination of both gram positive and gram negative bacteria species compared to the chemomechanical preparation alone.