The purpose of this study is to investigate if the use of systemic adjunctive antibiotics in the treatment of periimplantitis is needed.

This study will give the opportunity to draw scientifically based conclusions on the recommendations of the use of adjunctive systemic antibiotics in the treatment of peri-implantitis. This study will also be able to determine the ecological impact on the oropharyngeal and intestinal microflora between different antibiotic treatments. The lack of knowledge in this area has been highlighted by the Food and Drug Administration and The Swedish Council on Health Technology Assessment (SBU)

Inclusion Criteria:

1. Male or female ≥18-65 year
2. Patients who has been referred by a general dentist to a specialist clinic in periodontology for treatment of peri-implantitis.
3. Having sign of peri-implantitis around at least one osseointegrated dental implant that has been in function for ≥ one year
4. Peri-implantitis is diagnosed when; PPD of ≥ 6mm can be found at a dental implant in association with BOP and/or suppuration together with the loss of marginal alveolar bone of more than 2 mm detected on intraoral radiographs (giving radiographic exposure of at least ≥ 3 fixture threads).
5. Partially or completely edentulous subjects with healthy or treated periodontal conditions enrolled in a regular supportive program.
6. Full-Mouth Plaque Score (FMPS) ≤ 25
7. Signed informed consent

Exclusion Criteria:

1. Known allergy to amoxicillin, penicillin (PcV), metronidazole or betalactamic
2. Contraindication for dental surgical treatment (i.e. immunocompromised, uncontrolled DM (B-GHb-A1C 8-9 %, 64-75 mmol/mol), osteoporosis, I.V bisphosphonate treatment due to malignancy, pregnant and lactating women).
3. Incapability to perform basal oral hygiene measures due to physical or mental disorders.
4. Received systemic antimicrobial therapy in the past three months.
5. Currently on allopurinol, digoxin, disulfiram, lithium, busulfan, 5-fluorouracil, methotrexate, phenytoin, cyclosporine and warfarin.
6. Known severe chronic peripheral or central disease of the nervous system
7. Known alcohol abuse
8. Known hepatic encephalopathy
9. Known lactose intolerance, galactose intolerance
10. Untreated periodontal condition.
11. Implant showing sign of mobility.
12. Implants with bone loss exceeding 2/3 of the length of the implant or implants with bone loss beyond any transverse openings in hollow implants.
13. Any medical condition or on any concomitant medication that, in the opinion of the investigator, might interfere with the evaluation of the study objectives or jeopardize patient safety

Patients with xerostomia or having slow bowel motion will be excluded from the group of patients providing salivary and fecal samples.