The aim of this randomized clinical study is to assess the additional clinical benefit of incorporating a resorbable collagen membrane (CM) alongside a xenogeneic bone graft-specifically, deproteinized bovine bone mineral with 10% collagen (DBBM-C)-in the reconstructive surgical treatment of peri-implantitis involving combined (i.e., contained and non-contained) defect configurations.

Accordingly, the study addresses the following research questions:

• Does the adjunctive use of a CM in combination with DBBM-C improve treatment success compared to DBBM-C alone in the management of combined peri-implantitis-related defects?
• Does the combined use of a CM and DBBM-C lead to superior patient-reported outcomes (PROs) compared to the use of DBBM-C alone in the reconstructive treatment of such defects? A total of 60 patients who have been referred to the Gazi University Department of Periodontology will be randomly assigned to receive test (DBMM-C +CM) or control group (DBMM-C) treatments. Clinical parameters will be assessed at baseline (i.e., prior to surgery), and at the 6-, and 12-month post-operatively. Radiographic examinations will be carried out at baseline and 12 months post-operatively. Patient oral health related to the treatment procedures will be evaluated using a written questionnaire [Oral Health Impact Profile (OHIP-14)] prior to treatment and after 2 weeks, 1, and 12 months following surgical therapy. Regarding post-treatment pain and overall patient satisfaction with treatment modalities, responses will be scored on a visual analog scale (VAS, 100 mm).

Reconstructive surgical therapy for peri-implantitis has shown improved clinical and radiographic outcomes, with favorable postoperative mucosal margin levels and superior radiographic bone fill compared to other treatment modalities. However, no specific biomaterial or application technique has yet been identified as clearly superior. In particular, the potential added value of combining a barrier membrane with a bone substitute, as opposed to using bone substitute alone, remains a subject of ongoing debate.

Recent studies have suggested that the adjunctive use of a barrier membrane does not necessarily enhance clinical or radiographic outcomes in peri-implantitis-associated intrabony defects. However, these studies often included heterogeneous defect morphologies, which may influence the regenerative potential and confound treatment outcomes.

Indeed, "contained" and "non-contained" defects may behave differently due to biological factors such as space maintenance, clot stability, and wound protection. his highlights the need to tailor biomaterial selection to the specific defect configuration. While current evidence suggests that barrier membranes may not provide additional benefit in fully contained defects, there is a lack of data regarding their effectiveness in combined defects that include both supracrestal and intrabony components, particularly those with partially contained 2- or 3-wall morphologies.

Therefore, the primary aim of this randomized clinical study is to evaluate the additional clinical benefit of incorporating a resorbable CM with DBMM-C in the reconstructive surgical treatment of peri-implantitis with combined defect morphology.

The secondary objective is to assess patient-reported outcomes (PROs) in both treatment groups.

Inclusion Criteria:

• Peri-implantitis defined as the presence of a peri-implant probing pocket depth (PPD) ≥6 mm with bleeding and/or suppuration on probing (BoP/SoP) and radiographic marginal bone loss (MBL) ≥3 mm.
• Presence of combined defect configuration Class [Ib, Ic, Ie with horizontal components (i.e. Class II) (Schwarz et al., 2010)] with an intrabony compartment of ≥3 mm.
• Presence of a minimum width of 2 mm of keratinized peri-implant mucosa on the buccal aspect of the implant.
• Implants placed in proper position (inside the bony housing)
• Having an implant-supported prosthesis that allows for adequate oral hygiene procedures and peri-implant probing.

Exclusion Criteria:

• Full-mouth plaque score (FMPS) < 25%
• Full-mouth bleeding score (FMBS) < 25%
• Cigarette smoking < 10 cig./day,
• Diagnosed with active periodontal disease,
• Having acute or chronic medical conditions or undergoing medications, such as intravenous amino-bisphosphonates, immunosuppressive drugs, and chemotherapy, that could interfere with the treatment outcome,
• Receiving antibiotic treatment in the previous 3 months.