The aim of this randomized controlled study is to evaluate the outcome of surgical treatment of peri-implantitis with and without the use of a bone substitute graft covered by a collagen membrane. There will be a follow up period of 12 months. Outcome measures will include assessments of inflammation, probing depth, recession, radiological parameters and PROMs.

The aim of this randomized controlled study is to evaluate the possible benefit of a regenerative treatment protocol (placing a bone substitute covered by a bioresorbable collagen membrane) compared to surgical treatment alone, for peri-implantitis therapy.

The hypothesis is that there will be a greater number of patients with successful treatment of peri-implantitis following the use of a bone substitute/collagen membrane compared to surgical peri-implantitis therapy without the bone substitute/collagen membrane.

The project will be conducted as a two-armed randomized controlled clinical trial of 1-year duration. Forty systemically healthy patients with ≥1 implant diagnosed with peri-implantitis requiring surgical therapy will be enrolled.

Baseline measurements will be performed after non-surgical therapy (removal supramucosal biofilm/calculus, oral hygiene instruction and correction of prosthetic factors) and treatment of periodontitis.

Baseline measurements will include probing depth, position of mucosal margin, presence of plaque, presence of bleeding and/or suppuration on probing, PROMs and radiographs. Measurements will be recorded at 4 sites per implant.

Following the baseline measurements participants will be randomly assigned to either Control Group (Group 1): access flap and implant cleaning or Test Group (Group 2): access flap, implant cleaning and addition of a bone substitute material covered by a collagen membrane.

Participants in both treatment groups will be prescribed systemic antimicrobials (Amoxicillin 500 mg tds and Metronidazole 400 mg tds) for 7 days starting from the day of surgery.

In addition an antibacterial mouthrinse (chlorhexidine digluconate 0.2%) will be prescribed for a period of 4 weeks following surgery.

Participants will be asked to attend follow-up visits for review of healing (week 1 and 4) and maintenance care (3, 6, 9, and 12 months).

Clinical examinations will be performed by a calibrated blinded examiner at baseline and 12 months after therapy. Clinical measurements will be taken using a periodontal probe at 4 sites per implant to record presence of plaque, bleeding, probing depth and recession of the soft tissue.

PROMS will be assessed at 1 week, 4 weeks and at 12 months. Radiographic assessments Intra-oral radiographs and cone beam CT scan will be obtained prior to surgery and at 12 months. Oral-maxillofacial radiologists will. perform the radiographic analysis and will be blinded to the treatment procedure.

Primary outcome variables include (1) resolution of peri-implantitis (probing depth reduction and absence of BoP, suppuration) (2) recurrence of disease (BoP, suppuration and increase in PPD and progression of bone loss.

Inclusion Criteria:

Presence of ≥ 1 implant with a probing depth (PD) ≥ 5 mm with bleeding and/or suppuration (SUP) on probing, and peri-implant bone loss ≥ 3mm with an intraosseous defect component

Exclusion Criteria:

• Smokers > 10 cigarettes per day
• Patients with uncontrolled diabetes mellitus
• Pregnant or lactating women (self reported)
• Patients with a systemic illness that preclude them from oral surgery
• Patients with an allergy to amoxicillin or metronidazole or chlorhexidine.
• Patients requiring antibiotic prophylaxis and Patients who have taken antibiotics in the past 3 months