Objective: the objective of the present randomized clinical trial is to compare changes in radiographic peri-implant bone defect fill after regeneration of peri-implant intrabony defects with a submerged versus a non-submerged protocol.

Material and Methods: this project is a randomized controlled clinical trial, double blind, with a parallel groups design. Thirty-six patients presenting with peri-implantitis subsidiary of regenerative treatment will be recruited. After subjects have been given informed consent, they will be randomized to test or control group. All patients will undergo a session of non-surgical peri-implantitis therapy consisting on prostheses removal and implant debridement with ultrasounds, curettes and air-abrasive under local anaesthesia. Patients in test group will have their prostheses removed and the mucosa surrounding the affected implants will be let heal covering the implants, while patients in control group will have their prostheses installed again after the non-surgical therapy. Six to eight weeks later, all subjects will undergo regenerative treatment with the use of a bone substitute, a collagen membrane and fixation pins, and in control group tissues will heal following the non-submerged protocol, meanwhile subjects in test group will undergo submerged healing. Six months later, subjects in test group will have their prostheses reconnected to the regenerated implants. All patients will undergo periodontal and peri-implant maintenance therapy every three months during follow-up. Radiographic assessment of vertical bone level changes (primary outcome), clinical status of peri-implant tissues, changes in soft tissues margin, patient related outcomes and adverse events will be assessed at 3, 6 and 12 months after peri-implantitis regenerative surgery.

Inclusion Criteria:

• Patients diagnosed of peri-implantitis requiring surgical therapy
• The periapical radiographic study demonstrates an intra-bony component greater than 3 mm at the affected implant
• There is at least 2 mm of keratinized mucosa around the affected implant
• Intrasurgically, peri-implant defects must be type Ia, Ib, Ic and Ie (according to Schwarz et al. 2007)
• Affected implants must be two-piece implants to allow for the submerged protocol
• Affected implant supported restorations must be screw-retained or cemented, and should allow for prostheses removal

Exclusion Criteria:

• Patients with untreated periodontitis
• Medical conditions requiring prolonged use of steroids and/or medications that can interfere with bone metabolism
• Metabolic disorders such as osteoporosis
• History of uncontrolled endocrine disorders
• History of leukocyte dysfunction and deficiencies
• History of immunodeficiency syndromes
• History of neoplastic disease requiring the use of radiation of chemotherapy
• History of renal failure
• Physical handicaps that would interfere with the ability to perform adequate oral hygiene
• Alcoholism or drug abuse
• Smokers of more than 10 cigarettes per day, cigar equivalents or tobacco chewers
• Any other condition or circumstance that, in the opinion of the investigator, would prevent completion of study participation or interfere with the analysis of the study results, such as history of non-compliance or unreliability