en Oral & maxillofacial surgery Oral & maxillofacial surgery Original article Original article <strong>Background and aim: </strong>Antimicrobial photodynamic therapy (aPDT) has been suggested as a novel technique for decontamination of exposed implant surfaces. We aimed to evaluate the effect of aPDT on sandblasted, large-grit, acid-etched (SLA) titanium discs contaminated with <em>Eikenella corrodens</em> (<em>Ec</em>) and <em>Aggregatibacter actinomycetemcomitans</em> (<em>Aa</em>).<br> <strong>Materials and </strong><strong>m</strong><strong>ethods: </strong>In this in-vitro study, twenty-four sterile SLA titanium discs were contaminated with <em>Ec</em> (PTCC^&reg; 1391) and <em>Aa</em> <span dir="RTL">)</span>ATCC^&reg; 33384<span dir="RTL">(</span> and were randomly divided into the following groups: aPDT-treated group consisted of 12 discs submerged in 1 ml of toluidine blue and exposed to a low-level laser; negative control group comprised of 6 discs rinsed with physiological saline, and positive control group included 6 discs submerged in 2 ml of 0.2% chlorhexidine (CHX). After serial dilution, each sample was cultivated in an anaerobic environment (24 hours for <em>Ec</em> and 48 hours for <em>Aa</em>). Microbial reduction rate was calculated through colony-forming unit (CFU) counting according to Kruskal-Wallis test.<br> <strong>Results</strong>: The number of colonies for both bacterial strains in the aPDT-treated group was significantly reduced compared to the negative control group, showing the bactericidal potential of aPDT with toluidine blue (P<0.0001). The 0.2% CHX group showed a significantly smaller amount of colonies (CFU=1.089&times;10⁷ for <em>Ec</em> and 3&times;10⁷ for <em>Aa</em>) compared to the aPDT-treated group (CFU=3.73&plusmn;1.19&times;10⁹ for <em>Ec</em> and 52&plusmn;13.6&times;10⁵ for <em>Aa</em>; P<0.00001).<br> <strong>Conclusion</strong>: aPDT with toluidine blue significantly reduces <em>Ec</em> and <em>Aa</em> contamination of SLA titanium discs; however, 0.2% CHX showed the highest bactericidal potential and is still considered the gold standard in antimicrobial treatment of peri-implant diseases.<br> &nbsp; Decontamination, Titanium, Photodynamic Therapy, Eikenella corrodens, Aggregatibacter actinomycetemcomitans 18 25 http://jrdms.dentaliau.ac.ir/browse.php?a_code=A-10-579-1&slc_lang=en&sid=1 MR Karimi mrkarimip@hotmail.com 100319475328460010603 100319475328460010603 No Department of Periodontics, Faculty of Dentistry, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran M Montazeri mosimont@gmail.com 100319475328460010604 100319475328460010604 Yes Periodontist, Private Practice, Shiraz, Iran M Harandi drmohammadharandi@gmail.com 100319475328460010605 100319475328460010605 No Periodontist, Private Practice, Tehran, Iran L Aghazadeh Laleh_Aghazadeh@yahoo.com 100319475328460010606 100319475328460010606 No Dentist, Private Practice, Tehran, Iran L Aghazadeh Ladan_Aghazadeh@yahoo.com 100319475328460010607 100319475328460010607 No Dentist, Private Practice, Tehran, Iran