Inclusion Criteria:  a) males and females with ≥ 18 years; b) stage 3 generalized periodontitis; c) 3-6 months after step 1 and 2 of periodontal treatment, at least two non-adjacent teeth showing one residual pocket with probing depth (PD) ≥5, without mobility and without furcation involvement.  Exclusion Criteria:  : a) full-mouth plaque score (FMPS) and full-mouth bleeding score (FMBS) >20%; b) inadequate restorative therapy or malocclusion; c) uncontrolled systemic disease; d) immunosuppressive therapy or therapy with corticosteroid or with bisphosphonates; e) inflammatory and autoimmune diseases of the oral cavity; f) history of malignancy, radiation therapy or chemotherapy for malignancy in the last 5 years; g) insulin-dependent diabetes; h) smoking (> 10 cigarettes per day); i) drug and alcohol abuse; l) pregnant or lactating.