The purpose of this study is to test the comparative efficacy of two surgical approaches (immediate versus delayed GBR) for the surgical reconstruction of peri-implantitis intra-bony defects in terms of the clinical, radiographical, histological, volumetric, microbiological, and patient-reported outcomes.

The investigators hypothesize that in certain clinical situations, treatment of peri-implantitis intra-bony defects with the use of a compound bone grafting material (mixture of allogenic bone substitutes) and a non-resorbable barrier membrane and following a delayed approach (test group) with initial phase of defect decontamination and initial healing phase would yield superior outcomes to that of the conventional approach (control group) of defect decontamination and regeneration at the same clinical visit while also significantly enhancing patient-reported outcomes:

H0: There is no difference between the two mentioned approaches in terms of the treatment outcomes. H1: There is a significant difference, favoring the delayed approach compared to the immediate reconstruction.

Inclusion Criteria:

• Systemically healthy adults
• Age ≥ 18 years
• The patient must be able to perform good oral hygiene
• With at least one implant with either cement or a screw-retained prosthesis demonstrating a diagnosis of peri-implantitis at an implant in function for a minimum of 1 year with a prosthesis installed.
• In cases where previous radiographic records are available: presence of bleeding and/or suppuration on gentle probing, increased probing depth compared to previous examinations, and radiographic evidence of bone loss beyond initial crestal remodeling. (Berglundh 2018).
• In cases where baseline radiographs are not available: presence of PPD ≥6 mm with BOP and/or suppuration (SUP) and radiographically detectable marginal bone loss (MBL) exceeding 3 mm on an implant in function forfor at least 1 year (Berglundh 2018).
• Target implants have to also demonstrate the presence of a peri-implant intra-bony defect with a depth ≥3 mm and width ≤4 mm, as assessed on radiographs and confirmed intra-surgically. In addition, the bony defect should present with a minimum of two walls .

No implant mobility and no evidence of occlusal overload. In patients presenting with more than one implant meeting the inclusion criteria, a single implant will be randomly selected for inclusion in the study.

Exclusion Criteria:

• Short implants (≤ 6mm)
• Contraindications for undergoing oral surgery.
• Patients pregnant or attempting to get pregnant (self-reported), or nursing women.
• Untreated/active periodontitis, or other untreated acute infections at the surgical site.
• Untreated malignancies at the surgical site.
• Self-reported current smoking, or active tobacco chewing, or chronic vaping.
• Taking long-term (>1yr) NSAID, prednisone or other anti-inflammatory prescription drugs
• Patients with any known history of blood disorders or complications such as abnormal concentration of thrombin and factor XIII in plasma, or hemophilia.
• Patients with significant co-morbidities, such as obesity, uncontrolled diabetes, immunosuppression, severe endocrine-induced bone diseases, signs of malnourishment, those receiving immunosuppressive therapy, poor tissue oxygenation or perfusion, and pre- or post-operative radiation.
• Unable to give consent for participation.

There are several patient level variables that can be used to identify the patient when used in combination.