The objective of this randomized controlled clinical trial is to evaluate the outcome of treatment of peri-implantitis with or without systemic antibiotics.

Specific aims are to analyze (i) the effect of systemic antibiotics and local antiseptics on the healing process, and (ii) the risk for recurrence of disease following surgical treatment of peri-implantitis.

The study is designed as a randomized controlled clinical trial. 100 patients with severe peri-implantitis at one or more implants needing surgical treatment will be recruited. All individuals have to show unremarkable general health and not been using any antibiotics during the 6 months preceding the current examination.

The patients will be randomly assigned to the following :

• test group (T) : surgical treatment with systemic antibiotics,
• control group (C) : surgical treatment without systemic antibiotics. A stratification protocol will be applied regarding distribution of smokers. Two subgroups will be formed among test and control subjects.
• saline group (T1 and C1) : the exposed implant surfaces will be cleaned 3 minutes with saline during the surgical treatment, and,
• antiseptics group (T2 and C2) : the exposed implant surfaces will be cleaned 3 minutes with antiseptics (chlorhexidine 0,2%) during the surgical treatment.

A stratification protocol will be applied regarding distribution of smokers.

Following the baseline examination, patients will randomly be assigned to the various treatment group. Samples from the subgingival microbiota will be obtained before surgical therapy.

All patients will be enrolled in a hygiene program including professional supragingival implant/tooth cleaning using rubber cups and polishing paste and oral hygiene instructions.

The following clinical parameters will be measured at baseline using a periodontal probe: plaque index, Bleeding on Probing, probing depth measured from the mucosal margin to the bottom of the probable pocket and mucosal recession measured from a fixed landmark on the implant to the mucosal margin.

The measurements will be made at 4 aspects of each implant. In the test group (T) a systemic antibiotic regimen will be initiated at 3 days before surgery and continued for 10 days. (2 x 750mg amoxicillin/day or 2 x 1g amoxicillin/day depending on the weight of the patient) Intra-oral radiographs will be taken at 2 weeks and 1 year after surgical therapy.

The professional implant/tooth cleaning and reinforcement of oral hygiene will be performed at 2 weeks, 1, 2, 3, 6, and 12 months after treatment.

Examination of clinical outcome variables will be performed at 3, 6 and 12 months after surgical therapy. Microbiological samples will be obtained at the same time points. Radiographs are taken 2 weeks post surgical and at the one year examination.

Primary outcomes variables include: (i) clinical signs of resolution of peri-implantitis (pocket closure and absence of BoP), (ii) recurrence of the disease (BoP and increase in PPD) and (iii) further loss in marginal bone support, and (iiii) microbiological findings.

Inclusion Criteria:

• peri-implant probing pocket depth > 7 mm on at least one aspect of the implant, together with BOP and/or suppuration,
• marginal bone loss > 3mm as detected in radiographs.

Exclusion Criteria:

• implant mobility,
• peri-implantitis associated bone defects not suitable for pocket elimination therapy,
• systemic diseases that could influence the outcome of the therapy,
• penicillin allergy.