Inclusion Criteria:  Signed Informed Consent Form. Male and female subjects, aged 18-75 years, with diagnosis of severe generalized periodontitis. Good general health (free of systemic diseases such as diabetes, HIV infection or genetic disorder, ongoing malignant disease of any type that could influence the outcome of the treatment and might interfere with the evaluation of the study objectives). Diagnosis of Stage III-IV periodontitis; At least 6 sites per quadrant with Pocket Probing Depth (PPD) ≥ 3mm; At least 5 teeth per quadrant; Availability for the 3-month duration of the study for an assigned subject.  Exclusion Criteria:  Severe Smoking more than 10 cigarettes per day Pregnancy or nursing. Radiotherapy or Chemotherapy. BPCO (chronic obstructive pulmonary disease), asma. Systemic long-term corticosteroid treatment. Antibiotic treatment in the period of 3 months before the start of the study. Non surgical therapy in the period of 3 months before the start of the study.