The main aim will be to evaluate the difference in PD changes at 12-month follow-up, measured from the gingival margin to the base of the pocket, comparing periodontal regeneration using two different bone substitutes, that is bovine derived xenograft granules (BioOss® Collagen) and one resorbable sponge-like hydroxyapatite collagen matrix (OssixTM Bone), in adjunct with EMD after microsurgical flap elevation.

Inclusion criteria I. Men and women over or equal to the age of 18 years II. Patients in general good health in the opinion of the principal investigator as determined by medical history and clinical examination (ASA 1 or ASA-2) III. Clinical evidence of periodontitis, with one interdental area of PPD (periodontal probing depth) ≥6mm and bleeding on probing, associated one or more one-wall or two-wall intrabony periodontal defect with an intrabony component of equal or more than 3 mm, as diagnosed by periapical radiographs and clinical evaluation (excluding third molars and distal of second molars); the defect must not affect the vestibular / buccal or the lingual support bone wall (PPD lingual or vestibular / buccal <= 3.5 mm ) of the affected teeth.

IV. Patients who already underwent stage I and stage II of periodontal therapy, as described in the EFP practice guidelines (Sanz et al., 2020), within 6 months prior to assessment for eligibility V. Patients who can understand the requirements of the study and are willing and able to comply with its instructions and schedules VI. Patients who had provided written informed consent to participate in the study prior to any study procedure.

Exclusion criteria I. FMPS% > 15% at the time of recruitment II. FMBS% > 15% at the time of recruitment III. Treatment with anticoagulant drugs (INR above 2,5) IV. Treatment with intravenous bisphosphonates V. Treatment with anticonvulsants drugs VI. patients with history of alcohol, narcotics, or drug abuse VII. Patients receiving radiotherapy, chemotherapy, or any other immunosuppressive treatment or who have been administered radiotherapy in the last 5 years VIII. Patients through at any time received radiotherapy to the head and neck region will be excluded anyway IX. Uncontrolled bleeding disorders such as: hemophilia, thrombocytopenia, granulocytopenia X. Degenerative diseases XI. Osteoradionecrosis XII. Renal failure XIII. Organ transplant recipients XIV. HIV positive (self-declaration) XV. Malignant diseases XVI. Diseases that compromise the immune system XVII. Unbalanced diabetes. (HbA1c above 7.2 assessed by self-declaration) XVIII. Psychotic diseases XIX. Hypersensitivity or specific contraindications to one of the components of any of the products used in the study XX. Women who are pregnant (self-declaration); or lactating at the time of recruitment and of surgery XXI. Site where a history of failed periodontal regenerative procedure in the last two years XXII. Heavy Smokers (5 cigarettes and more per day) XXIII. other uncontrolled systemic diseases XXIV. disorders or treatments that compromise wound healing XXV. chronic high dose steroid therapy XXVI. bone metabolic diseases

Inclusion Criteria:

• Men and women over or equal to the age of 18 years
• Patients in general good health in the opinion of the principal investigator as determined by medical history and clinical examination (ASA 1 or ASA-2)
• Clinical evidence of periodontitis, with one interdental area of PPD (periodontal probing depth) ≥6mm and bleeding on probing, associated one or more one-wall or two-wall intrabony periodontal defect with an intrabony component of equal or more than 3 mm, as diagnosed by periapical radiographs and clinical evaluation (excluding third molars and distal of second molars); the defect must not affect the vestibular / buccal or the lingual support bone wall (PPD lingual or vestibular / buccal <= 3.5 mm ) of the affected teeth.
• Patients who already underwent stage I and stage II of periodontal therapy, as described in the EFP practice guidelines (Sanz et al., 2020), within 6 months prior to assessment for eligibility
• Patients who can understand the requirements of the study and are willing and able to comply with its instructions and schedules
• Patients who had provided written informed consent to participate in the study prior to any study procedure.

Exclusion Criteria:

• FMPS% > 15% at the time of recruitment
• FMBS% > 15% at the time of recruitment
• Treatment with anticoagulant drugs (INR above 2,5)
• Treatment with intravenous bisphosphonates
• Treatment with anticonvulsants drugs
• patients with history of alcohol, narcotics, or drug abuse
• Patients receiving radiotherapy, chemotherapy, or any other immunosuppressive treatment or who have been administered radiotherapy in the last 5 years
• Patients through at any time received radiotherapy to the head and neck region will be excluded anyway
• Uncontrolled bleeding disorders such as: hemophilia, thrombocytopenia, granulocytopenia
• Degenerative diseases
• Osteoradionecrosis
• Renal failure
• Organ transplant recipients
• HIV positive (self-declaration)
• Malignant diseases
• Diseases that compromise the immune system
• Unbalanced diabetes. (HbA1c above 7.2 assessed by self-declaration)
• Psychotic diseases
• Hypersensitivity or specific contraindications to one of the components of any of the products used in the study
• Women who are pregnant (self-declaration); or lactating at the time of recruitment and of surgery
• Site where a history of failed periodontal regenerative procedure in the last two years
• Heavy Smokers (5 cigarettes and more per day)
• Other uncontrolled systemic diseases
• disorders or treatments that compromise wound healing
• chronic high dose steroid therapy
• bone metabolic diseases