34 patients diagnosed with mild to moderate peri-implantitis, defined as 2-4 mm peri-implant bone loss, will be randomized to either test treatment with Labrida BioClean® or control treatment with titanium curettes. In total 40 subjects (20 % drop-out rate), treated by 5 clinicians at 5 centers will be included in the study.

4.1 Study design The study will be a prospective multicentre randomized, examiner blinded controlled clinical trial of 24 months duration. Change in mucosal inflammation will be reported after 6 months while the true endpoint parameters i.e., peri-implant attachment will be reported after 1 and 2 years.

4.2 Treatment allocation and blinding Patients will be allocated either to test (Labrida BioClean® or control (titanium curettes) treatment by computer-generated block randomization to ensure equal sample sizes. The examiners will be blinded to the treatment allocation.

4.3 Study setting In total six centres will be included. Patient screening, inclusions and all clinical examinations will be performed by a board-certified specialist in periodontology, registered dental hygienist or specialist in prosthetics at each centre. Treatments will be performed by a dental hygienist or a board-certified specialist in periodontology.

4.4 Patients 40 patients (20+20) diagnosed with mild to moderate peri-implantitis, defined as peri-implant bone loss 2 -4 mm, will be included in the study.

4.5 Recruitment of patients

Patients referred to or seeking care in the included clinics will be screened for inclusion.

Inclusion Criteria:

• Peri-implantitis defined as 2-4 mm bone loss distally, mesially or both, Probing Pocket Depth (PPD) ≥4mm and inflammation as demonstrated by Bleeding on Probing (mBoP) at least score 2.

In addition to the above mentioned main inclusion criteria, patients can be included if they meet the following conditions:

1. Peri-implantitis as defined above on an implant that has been in function for more than 12 months prior to study start.
2. Above 18 years of age.
3. Eligible for treatment in an outpatient dental clinic (ie, ASA I and II).
4. Had full-mouth plaque scores ≤20% prior to final inclusion and no visual plaque at the included implants prior to study start.
5. Had at least one implant with a loading time of ≥ 12 months prior to baseline.
6. Signed Informed Consent obtained prior to start.
7. Psychological appropriateness.
8. Consent to complete all follow-up visits.

Exclusion Criteria:

Peri-implant bone loss > 4 mm, radiotherapy, chemotherapy, systemic long-term corticosteroid treatment, pregnancy or nursing, anatomical abnormalities, prosthetic factors making access to clinical measurements impossible.

In addition to the above mentioned main exclusion criteria, patients should be excluded if they meet any of the following conditions:

1. Cemented supraconstructions and/or screw retained supraconstructions that for technical reasons makes it impossible to access implant for clinical measurements.

2. Technical complications which according to the examiners judgement has contributed to the disease state and not possible to resolve prior to final inclusion.

3. Mobile implant.

4. Patients diagnosed with periodontal disease must have undergone causative treatment and be re-evaluated.

5. Implants previously treated for peri-implantitis with grafting materials.

6. Receiving medications known to induce mucosal hyperplasia.

7. Uncontrolled diabetes HbA1c > 52, equals 7.0.

8. Receiving systemic antibiotics < 3 months prior to inclusion.

9. Pregnant or lactating.

10. Any condition or current treatment for any condition, which in the opinion of the investigator and/or consulting physician, may constitute an unwarranted risk.

11. Presence of psychological characteristics, such as inappropriate attitude or motivation, which will influence treatment execution and treatment outcome.

12. Unwillingness to undergo treatment.

13. Advanced, untreated and uncontrolled peri-implantitis on neighbouring implants.

14. If, in the opinion of the therapist, conditions are such that dental implants are deemed failing.

15. Ongoing or previous radiotherapy to the head-neck region.

16. Ongoing or previous chemotherapy.

17. Systemic long-term corticosteroid treatment.

18. Patients medicating with warfarine products or similar.

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Examiners blinded to treatment allocation since treatment is performed by a dental hygienist.