The photodynamic therapy is a light induced, athermal procedure for the inactivation of pathogenic microorganisms. In Part 2 of his introducing lecture about this procedure Dr. Steffen Rieger M.Sc., Germany, focuses on the integration of photodynamic therapy in the treatment concept of chronic periodontitis. The chronic periodontitis is a bacterial infectious disease which goes along with inflammatory degradation of the periodontium. Basis of a successful treatment is a subgingival debridement, achieved by scaling, root planing and adjunctive methods like systemic antibiotic treatment. The photodynamic therapy is a adjunctive method, too. It is effective against all the pathogenic germs, it has no side effects. Maybe in the deeper parts of the biofilm the effect is not that strong, subgingival concrements have to be removed mechanically before anyway. There are already some clinical studies which observed a slightly higher reduction of the gingival pocket depth and moderate win of attachment after the application of photodynamic therapy. For a general introduction to the active principle of photodynamic therapy see Dr. Rieger's lecture pt.1; for clinical procedure watch Dr. Rieger's case study, too.