Endodontic treatment is the clinical management of a microbiological problem (1
) and the main target of treatment is the microorganisms residing within the root canal system (2
). However, the complexity of the root canal system makes complete debridement and removal of bacteria with instrumentation, irrigation and intracanal medicaments virtually impossible (3
). In addition, current endodontic procedures require very good technical skills, and use medicaments whose effectiveness has never been definitively proven in human clinical trials. Three systematic reviews (4
) on the outcome of primary non-surgical root canal treatment summarized findings from longitudinal clinical studies published up to 2006, in which treatments were carried out by undergraduate students, graduate students, general dental practitioners or specialists. The estimated success reported in these studies was 75% (6
) and 78% (4
). In a recent systematic review by Ng et al.
(2010) that included fourteen studies published between 1993 and 2007, the pooled proportion of teeth surviving over 2–10 years following root canal treatment was found to range between 86% and 93% (7
). However, Wu et al.
(2009) reported several factors that contribute to the overestimation of successful outcomes after primary root canal treatment: A high percentage of cases confirmed healthy by periapical radiography reveal apical periodontitis on cone beam computed tomography and by histology; extractions and retreatments were rarely recorded as failures; and the recall rate was often < 50% in longitudinal clinical studies (8
). General dentists perform about 75% of root canal procedures (9
), and thus it might be anticipated that failure rates are even greater in general practice (6
). When strict radiographic criteria were used, the success rates were approximately 66%, 75%, 77% and 85% for treatments carried out by general dental practitioners, undergraduate students, graduate students and specialists, respectively (6
). Given that more than 20 million root canals are performed yearly in the U.S. (10
), approximately 2 million endodontic failures could be avoided by better disinfection procedures. The development of adjunctive antibacterial therapeutic strategies to CMD therefore becomes important in the evolution of methods to target residual microorganisms in the root canal system.
Photodynamic therapy (PDT) was developed as a therapy for cancer and is based on the concept that a non-toxic photosensitizing agent, known as photosensitizer, can be preferentially localized in premalignant and malignant tissues and subsequently activated by light of the appropriate wavelength to generate singlet oxygen and free radicals that are cytotoxic to cells of the target tissue (11
). In recent years, PDT has been employed to target microorganisms in root canals in vitro
) and in vivo
) suggesting its usefulness as an adjunct to current endodontic disinfection techniques. Methylene blue (MB) is a well-established photosensitizer that has been used in PDT for targeting various gram-positive and gram-negative oral bacteria (33
) and was previously employed to study the effect of PDT on endodontic disinfection (14
). MB has been used as a photosensitizing agent for almost nine decades (34
). It has been used for the detection of mucosal premalignant lesions (35
) and as a marker dye in surgery (36
). The hydrophilicity of MB (37
), along with its low molecular weight and positive charge allows passage across the porin-protein channels in the outer membrane of gram-negative bacteria (38
). MB, whose intravenous administration is FDA approved for methemoglobinemia, predominantly interacts with the anionic macromolecule lipopolysaccharide and results in the generation of MB dimers (38
), which participate in the photosensitization process (38
The objective of the present study was to evaluate the antimicrobial effects of MB-mediated PDT in a stringent and clinically relevant evaluation using naturally human infected teeth ex vivo
treated immediately upon their extraction. Teeth with radiographic evidence of periradicular lesions were chosen because they were guaranteed to be grossly infected, which mimics the clinical situation that leads to higher failure rates (2
). The use of naturally-infected teeth, which contain a much broader range of pathogens and deeper penetration into tubules than any in vitro
model system provides an excellent test of the potential of PDT in achieving root canal disinfection.