RESUMO
INTRODUCTION: The aim of the present study was to investigate ex vivo by confocal laser scanning microscopy the antibacterial effect of photodynamic therapy (PDT) on dentinal tubules in the apical 5 mm of human mandibular premolars contaminated with Enterococcus faecalis. METHODS: Thirty-four teeth were standardized to 20 mm and foraminal anatomic diameters using a #20 K-file (Dentsply Maillefer). Samples were contaminated for 21 days and divided into the following 3 experimental groups (n = 10): the PDT group (instrumented canals and PDT), the passive ultrasonic irrigation (PUI) group (instrumented canals and PUI), and the PUI-PDT group (instrumented canals, PUI, and PDT), along with a control group (n = 4) (noninstrumented canals). The canals in the experimental groups were instrumented with ProTaper Next (Dentsply Maillefer) up to X3 and rinsed with EDTA and sodium hypochlorite. The photosensitizer used was 0.01% methylene blue with a preirradiation time of 5 minutes and a diode laser with 4 J energy and a 660-nm wavelength. Cross sections were made 5 mm from the apex of all samples, which were analyzed using confocal laser scanning microscopy. The results were analyzed using the Shapiro-Wilk and Kruskal-Wallis (Dunn) tests. RESULTS: There was a lower percentage of live bacteria in the PUI-PDT group, with a statistical difference compared with the control and PDT groups (P < .05). There was no statistical difference in the percentage of live bacteria between PUI-PDT and PUI (P > .05). CONCLUSIONS: It was concluded that the PUI-PDT association was most effective in disinfecting root canals compared with the control group and PDT.