 The goal of periodontal treatment is to restore tissue health through the elimination and control of etiologic factors, reducing the microbial aggression. Some microorganisms persist in the root surface even after scraping. Thus, the conventional mechanical treatment may fail to reduce the number of periodontal pathogens to levels compatible with health. This study will verify the efficacy of Photodynamic Therapy PDT as an adjunct to non-surgical treatment of chronic periodontitis. 