Objective. Photodynamic therapy has been expanded for use in endodontic treatment. The aim of this study was to investigate the antimicrobial effects of diode laser irradiation on endodontic pathogens in periapical lesions using an in vitro apical lesion model. Study Design. Enterococcus faecalis in 0.5% semisolid agar with a photosensitizer was injected into apical lesion area of in vitro apical lesion model. The direct effects of irradiation with a diode laser as well as heat produced by irradiation on the viability of microorganisms in the lesions were analyzed. Results. The viability of E. faecalis was significantly reduced by the combination of a photosensitizer and laser irradiation. The temperature caused by irradiation rose, however, there were no cytotoxic effects of heat on the viability of E. faecalis. Conclusion. Our results suggest that utilization of a diode laser in combination with a photosensitizer may be useful for clinical treatment of periapical lesions. 1. Introduction It is generally accepted that disinfecting processes are essential for successful root canal treatment, and antimicrobial irrigants to remove microorganisms are important for chemomechanical preparation of a root canal [1, 2]. Endodontic irrigants are required to have a broad spectrum of antimicrobial activities, as well as a relative lack of toxicity against sound periapical tissue. Sodium hypochlorite (NaOCl) is a major endodontic irrigant, however, it has cytotoxic and neurotoxic effects when extruded into periapical tissues [3, 4]. To develop a safe endodontic irrigants, ozonated water was previously examined as an endodontic irrigant and demonstrated to be a useful irrigant for removal of microorganisms from root canals without damage to other tissues [5]. However, it is also known that complete elimination of microorganisms from root canals and periapical lesions by antimicrobial irrigants only is difficult, because of the anatomical complexities of root canals, deep invasion of microorganisms into dentinal tubules, and formation of biofilms on the surface of root apex, resulting in persistent apical periodontitis [6–8]. In addition, several studies have reported that the lack of response of refractory periapical lesion is due to the in inaccessibility of the extraradicular microorganisms or to the presence of microorganisms [9–11]. Recently, photodynamic antimicrobial chemotherapy has received focus as an alternate antibacterial, antifungal, and antiviral treatment for drug-resistant microorganisms [12, 13]. Along that line, disinfection of root canals by laser
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