A 6-month multicenter prospective consecutive case series was performed in six different periodontal specialist clinics in Norway, Sweden and Italy.

Ethical approval was provided by the regional ethical review boards of each center (Norway: 2014/852/REK sør-øst; Italy: Sapienza 2011/15, 3547; and Sweden: EPN Lund 2014/695.) Fifteen patients at each center were planned to be included in the study. Patient screening, inclusions and all clinical examinations were performed by board-certified specialists in periodontology. Subjects were included in the study if they had at least one implant that had been in function for more than 12 months and had been diagnosed with mild peri-implantitis defined as 1–2-mm bone loss, pocket probing depth (PPD) ≥4 mm and a positive bleeding on probing score. Patients diagnosed with periodontitis were required to be finished with active periodontal treatment prior to inclusion in the study. All six surfaces of the included implants were free of supragingival visible plaque. Patients were required to have a total plaque score (dichotomous scoring) below 20% prior to inclusion, and baseline measurements were performed after careful oral hygiene instruction on an individual, as-needed basis. Radiographs were taken at baseline and at the 6 months evaluation. Endodontic lesions and dental decay should have been treated prior to inclusion. Clinical examinations were performed at baseline and at 2, 4, 12 and 24 weeks after baseline using a 0.20-N (20-g)-defined force periodontal probe (University of North Carolina, DB764R, AESCULAP, B Braun Germany). PPD and mBoP was recorded at six sites per implant. Bleeding on probing (mBoP) was recorded using a 3-graded index 30 s after probing as follows: A score of 0 represented no bleeding, 1 represented isolated minimal bleeding spots, 2 represented blood forming a confluent red line on the margin and 3 represented heavy or profuse bleeding [22]. The clinical protocol also included scoring of the height of the gingival margin relative to the crown margin.