The primary objective of the study is to proof the successful use of Geistlich Bio-Oss® and Geistlich Bio-Gide® (already registered medical devices) in bony peri-implant defects due to peri-implantitis disease.

Patient who will considered eligible at the screening visit will undergo surgical treatment procedure within 2 weeks. At the day of the surgery the patients will be randomized into the 2 treatment groups.

The subjects will be then prescribed postoperative antibiotics (Azitromax 500 mg day one and 250 mg day 2-4).

Post-operative pain will be controlled with Ibuprofen (400mg x 3) for two days to all subjects. Subjects will rinse twice daily with Chlorhexidine mouth rinse and use modified oral hygiene procedures during the first 5 weeks of healing. Subjects will receive professional prophylaxis as required.

Subjects will be instructed on appropriate oral hygiene throughout the study and will be given appropriate oral hygiene instructions. Instructions on post-operative care will be repeated at each visit. In particular the following points have to be covered during the first month after surgery: Chlorhexidine rinses, avoidance of brushing, usage of interdental cleaning devices, avoidance of chewing on or trauma to the treated area. In addition subjects will be instructed not to smoke more than 10 cigarettes per day during the entire study period and not to consume alcohol during antibiotic therapy.

Sutures will be removed after 14 days. Photos will be taken during the whole study to document the healing process.

Further follow up visits will be scheduled 6 weeks and 3,6,9,12 months post-surgery.

Inclusion Criteria:

• age 18 years or older
• Presence of peri-implantitis
• A peri-implant intraosseous defect with at least 3 mm defect depth as seen on an intraoral radiograph.
• Clinically a probing depth ≥ 5 mm combined with bleeding and/or pus should be present at the site.
• During surgical exploration an intraosseous component of at least 3 mm at the deepest point must be present.
• The defect should have a minimum of 3 osseous walls (a circumference of the osseous defect of at least 270 degrees). Only 3 and 4 wall intraosseous defects will be included.
• Implants included in the study must have been in function for more than 12 months.
• Ability to fully understand the nature of the proposed surgery and ability to sign an Ethics Committee-approved informed consent form

Exclusion Criteria:

• Subjects with diabetes mellitus (HbA1c > 7.0)
• Subjects taking prednisone or other anti-inflammatory prescription drug
• Subjects taking medications known to have effects on gingival growth
• If the same patient has more than one defect meeting the inclusion criteria, only one such defect will be included in the study
• General contraindications for dental and/or surgical treatments
• Smokers (> 10 cigarettes per day).
• Pregnant or lactating women
• Allergy to collagen
• Inability to consent for participation in the study and/or to accept the proposed