Photodynamic therapy (PDT) has emerged in recent years as a non - invasive therapeutic modality for the treatment of various infections by bacteria, fungi and viruses. This therapy is defined as "an oxygen dependent photochemical reaction that occurs upon light - mediated activation of a photosensitizing compound leading to the generation of cytotoxic reactive oxygen species, predominantly singlet oxygen". Thus antimicrobial photodynamic therapy can be usedto eliminate periodontal pathogens selectively and thus periodontal disease can be treated successfully.