Randomized, surgeon and outcome assessor blinded, multi-centric, superiority trial with two parallel groups and a 1:1 allocation ratio with the aim of comparing the surgical treatment of severe peri-implantitis with or without an initial non surgical approach.

Inclusion Criteria:

Any patient having at least one implant affected by severe peri-implantitis, being at least 18 years old and able to sign an informed consent form will be potentially eligible for this trial.

Severe peri-implantitis will be defined as peri-implant probing pocket depth [PPD] ≥6 mm in at least 1 site of the implant, together with bleeding and/or suppuration on probing [BoP and/or SoP, respectively] and radiographically documented marginal bone loss/level ≥3 mm (Carcuac et al. 2016) on implants in function by at least 1 year. In case of absence of baseline radiographs, the reference point for baseline bone levels will be considered where bone was likely to be at implant placement.

Exclusion Criteria:

Patients fitting to all the inclusion criteria as above will be not included in the study if they appear to be unable to attend to the study-related procedures (including the follow-up visits) or if one or more of the following systemic or local exclusion criteria are found in the enrolment phase.

Systemic primary exclusion criteria:

• compromised general health which contraindicates the study procedures (ASA IV-VI patients);
• systemic diseases which could influence the outcome of the therapy (uncontrolled diabetes mellitus);
• pregnant or nursing women;
• chronic use of corticosteroids or NSAID or immune-modulator drugs (any type and any dose);
• patients who need use of medications affecting bone metabolism or peri-implant mucosa (bisphosphonates, any type and any dose).

Local primary exclusion criteria:

• history of peri-implantitis treatment on implants to be included in the study (included topical antibiotics);
• hopeless implants (e.g. mobility) to be included in the study.

Secondary exclusion criteria:

- uncompliant patients (poor oral hygiene 2 weeks after OHI).