This pilot study is an interventional clinical study on the supportive peri-implant treatment (SPiT) necessary to maintain/ improve the clinical conditions surrounding a dental implant following surgical treatment of peri-implantitis. The focus of this pilot, double arm, split-mouth, single centre, controlled, randomised clinical study is to examine the effect of short-term increased frequency of a SPiT-protocol.

Patients with surgically treated peri-implantitis enrolled in a maintenance program at the Specialist clinic, Institute for Clinical Dentistry, Dental Faculty, University of Oslo, will receive SPiT by the use of an oscillating chitosan brush (LBC, BioClean, Labrida AS, Oslo, Norway). Subjects with at least two not-adjacent implants of similar brand and defect configuration registered with suppuration or Bleeding index score 3-2 (Roos-Jansaker et al., 2007) on at least 1 of 6 surfaces (mesiobuccal, buccal, distobuccal, mesiolingual, lingual, distolingual) will be invited to participate in the current pilot study.

Baseline examinations and treatment:

Radiographs of the implants showing clear projections of the implant threads at the mesial and distal surfaces will be taken using standard Eggens holders

The following clinical registrations will be performed at six sites (mesiobuccal, buccal, distobuccal, mesiolingual, lingual, distolingual) of the included implants by the blinded examiner:

Suppuration: the presence or absence after light pressure against gingiva/mucosa or following gentle probing of the peri-implant pocket.

Plaque: the presence or absence recognized by running a probe across the marginal surface of the implant (Mombelli, van Oosten, Jr, & Lang, 1987).

Gingival bleeding: registered according to the Modified Sulcus Bleeding Index (mBI) (Mombelli et al., 1987).

PPD: recorded with a pressure- sensitive probe (20 g) (University of North Carolina probe, Aesculap, Braun, Tuttlingen, Germany).

Bleeding index score: measured at the implants after probing at six sites, and graded (0-3):

0 = no bleeding,

1. = spot bleeding,
2. = line bleeding
3. = profound bleeding within 30 seconds after measurement of PPD. Presence of keratinized mucosa: registered at the mid buccal site as "adequate" ≥2 mm, "inadequate" <2 mm (Moraschini, Luz, Velloso, & Barboza, 2017).

All included implants receive the following treatment:

Repeated oral hygiene instruction if needed Submucosal debridement with a chitosan brush (LBC, BioClean®, LABRIDA AS, Oslo, Norway) seated in an oscillating dental drill piece (ER10M, TEQ-Y, NSK Inc., Kanuma Tochigi, Japan) for 3 min followed by copious irrigation with sterile saline Supramucosal polishing using polishing paste and rubber cup Following treatment, if local anesthesia was not applied, the subjects will be asked to grade the level of pain experienced on a 10 cm visual analogue scale (VAS).

3-, 6- and 9 weeks following baseline At the 3-week follow up, an equal number of included implants are determined "test-" and "control-" by flipping of a coin.

At these time points, all implants are clinically examined by a blinded examiner and receive supramucosal polishing, but only test-implants receive submucosal debridement as described above (see figure 1) VAS scales are registered

12 weeks (3 month) following baseline At these time point, all implants are clinically examined by a blinded examiner and receive supramucosal polishing as well as submucosal debridement as described above (see figure 1) VAS scales are registered

16 weeks (4 month) following baseline All implants are clinically examined by a blinded examiner and receive supramucosal polishing, but only test-implants receive submucosal debridement as described above (see figure 1) VAS scales are registered

24 weeks (6 month) following baseline At these time point, all implants are clinically examined by a blinded examiner and receive supramucosal polishing as well as submucosal debridement as described above (see figure 1) VAS scales are registered

36 weeks (9 month) following baseline At these time point, all implants are clinically examined by a blinded examiner and receive supramucosal polishing as well as submucosal debridement as described above (see figure 1) VAS scales are registered Radiographs are taken according to the baseline examination

Figure 1: Timeline of the clinical trial

Inclusion Criteria:

• Subject must be ≥ 20 years,
• Subjects must have received surgical treatment of peri-implantitis as defined by the World Workshop 2017 criteria (Berglundh et al., 2018).
• Subjects have to present inflammation (suppuration or BoP 3-2) at more than one implant of similar implant brand, with similar defect type (Schwarz et al., 2007), and defect severity.
• The implants must not be replacing adjacent teeth (minimum space for one tooth/implant between test and control.

Exclusion Criteria:

• • Previous radiotherapy in the affected area, current use of chemotherapy, systemic long-term corticosteroid treatment.

  • No pregnant or nursing subjects.
  • < class 2 according to the ASA (American Society of Anesthesiologists) physical status classification.
  • Registered implant bone loss with exposed modified surface < 2.0 mm.
  • If examiners/operators agree the placement of the implant (angle, position, proximity to adjacent implant or tooth) or suprastructure was suboptimal and considered to play a major role in the development and sustain the peri-implant disease.
  • Anatomical abnormalities
  • clinical exclusion criteria specific to the disease/condition
  • specific concomitant treatment with other devise, mouthrinse or systemic antibiotics
  • participation in any other clinical study within the last month
  • inability to comprehend and respond to the quality of life questionnaire

The assessor will not participate in the treatment, is blinded to what implant receives which treatment and leaves the room following examination prior to treatment