Periodontitis is an infectious disease characterized by the destruction of supporting tissues. Antimicrobial photodynamic therapy (aPDT) has been proposed as an improved method for eliminating microorganisms. Its efficiency depends on the correct use of physical and chemical parameters. Thus, these parameters and their relations were evaluated in this study with the purpose of establishing lethal conditions for combating bacterial agents. Diode lasers and light-emitting diodes (LEDs) were characterized to evaluate the absorption profile and resonance of methylene blue (MB) and toluidine blue O (TBO). The relations between light energy density and photosensitizer absorption were determined. Two methodologies were used to evaluate the effects of aPDT against Aggregatibacter actinomycetemcomitans. LED light exhibited a broad emission spectrum with a peak light wavelength of 637 nm and 99% purity. The resonance intensity of MB was higher with diode laser irradiation, and TBO showed higher resonance intensity with LED irradiation. There was no difference in the absorption profile of photosensitizers using diode lasers or LEDs, and variations in power density did not result in an increasing or decrease in light absorption. A. actinomycetemcomitans was susceptible to photodynamic processes. Emission spectra and peak light wavelengths of light sources combined with the absorption profiles of photosensitizers were the main parameters involved in determining the efficiency of photodynamic effects. Power density did not alter the light absorption of photosensitizers. The association between adequate irradiation characteristics and photosensitizer absorption results in complete inactivation of A. actinomycetemcomitans. In addition, the bactericidal effect was not altered by an increase in energy densities.
