Contents lists available at ScienceDirect Photodiagnosis and Photodynamic Therapy journal homepage: www.elsevier.com/locate/pdpdt Comparison of diferent modes of photo-activated disinfection against Porphyromonas gingivalis: An in vitro study Reza Fekrazad a,b , Farzaneh Khoei c , Abbas Bahador d , Neda Hakimiha c, * a Radiation Sciences Research Center, Laser Research Center in Medical Sciences, AJA University of Medical Sciences, Tehran, Iran b International Network for Photo Medicine and Photo Dynamic Therapy (INPMPDT), Universal Scientific Education and Research Network (USERN), Tehran, Iran c Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran d Oral Microbiology Laboratory, Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran ARTICLE INFO Keywords: Porphyromonas gingivalis Antimicrobial photodynamic therapy Photothermal therapy Indocyanine Green ABSTRACT Background: Porphyromonas gingivalis (P. gingivalis), a Gram-negative periodontal pathogen, is frequently de- tected in subgingival plaques in patients with chronic periodontitis. Considering the insufcient results achieved by the current antimicrobial approaches, this study aimed to compare the susceptibility of P. gingivalis to the diferent modes of photo-activated disinfection in planktonic culture. Methods: Cultures of P.gingivalis were assigned into three main groups of photothermal disinfection with 810 nm laser in continuous mode+EmunDo® (indocyanine green based photosensitizer), 808nm laser in pulse mode + Perio green® (indocyanine green based photosensitizer); and antibacterial photodynamic therapy with 662 nm laser + Radachlorin® photosensitizer. Then, the bacterial viability was determined by serial dilution method by counting the number of colonies forming units. The results were analyzed by one-way analysis of variance and Tukey test (p < 0.05). Results: All three groups showed signifcant reduction in the viability of P. gingivalis (p < 0.001). However; this reduction was signifcantly higher in photothermal therapy with EmunDo®. Conclusions: Both methods of photodynamic and photothermal therapy were successful in Signifcant eradica- tion of P. gingivalis. Although, photothermal approach was more efcient with EmunDo® in combination with 810 nm laser irradiation. 1. Introduction Photochemical therapy, or use of an exogenous sensitizer to absorb photons in order to achieve therapeutic efect, has a long history [1]. The frst examination of photosensitized reactions in a scientifc way took place over a century ago when Rabb observed the lethal feature of acridine and visible light on Paramecium caudatum [2]. The essentiality of light and oxygen was later illustrated by Von Tappeiner [3]. This process is called photodynamic therapy (PDT) in which cytotoxic sub- stances such as singlet oxygen and free radicals are produced as the result of the activation of photoreactive compounds – photosensitizers (PS) after the irradiation of light with an appropriate wavelength [4]. Singlet oxygen is a highly reactive molecule. It can cause oxidative destructive reactions on the cell membrane and cell wall leading to cell death [5,6]. Recently, an oxygen-independent photochemical me- chanism has been proposed by Hamblin et al. in PDT. They stated that, specifc PSs like psoralens and tetracyclines can bind to a defned molecular structure inside their target microorganism and then activate with short wavelength light (UVA or blue) in the absence of oxygen. It can cause bacteria death by formation of covalent adducts in bacterial DNA or ribosome. They also proposed the addition of several diferent inorganic salts to achieve antibacterial efect in the absence of oxygen [7]. PDT has primarily been studied and developed as a treatment option for cancer, ophthalmologic disorders, gastric ulcers, skin diseases, and wound healing [8]. Attention to its antibacterial efect has recently invigorated, so it has been applied for a large variety of localized dis- eases with microbial origin as a treatment method named Antimicrobial Photodynamic Therapy (aPDT) [9]. Singlet oxygen has extremely short lifetime in biological systems with a very short radius of action about 0.02μm. This feature can provide a localized antimicrobial efect without afecting the distant cells [5,10]. The discovery of antibiotics during the mid-last century, prevented exploiting the potential of PDT against infectious diseases. Antibiotics administration can cause https://doi.org/10.1016/j.pdpdt.2020.101951 Received 21 June 2020; Received in revised form 5 August 2020; Accepted 7 August 2020 ⁎ Corresponding author at: Laser Research Center of Dentistry, Dentistry Research Institute Tehran University of Medical Sciences, Qods street, Enqelab Street, Tehran 1417614411, Iran. E-mail address: ned.hakimiha@gmail.com (N. Hakimiha). Photodiagnosis and Photodynamic Therapy 32 (2020) 101951 Available online 17 August 2020 1572-1000/ © 2020 Elsevier B.V. All rights reserved. T