Light, either alone or in combination with chemical compounds, has been used for its therapeutic and antimicrobial effects. Photodynamic therapy encompasses the simultaneous action of a light source and photosensitizing agent in the presence of oxygen in tissues. Individually, each of these substances is innocuous, but their interaction is capable of giving rise to cytotoxic species that lead to cell death.The advantage of this approach is the avoidance of the development of resistance on the part of the target bacteria and damage to the adjacent tissues, since the antimicrobial effect is confined to the area covered by the dye and irradiated by the light, acting quickly on the target organisms. The efficacy of photodynamic therapy depends on the energy dose and output power employed.