This randomized clinical trial evaluates the clinical and microbiological (microbial complexes and changes in the diversity of the submucosal biofilm) effects of MTZ+AMX as adjuncts to anti-infectious surgical treatment plus Er: YAG in the treatment of peri-implantitis.

Peri-implantitis is a pathological condition characterized by inflammation of peri-implant connective tissues and progressive peri-implant bone. Recently, the therapeutic protocol using non-surgical debridement associated with the combination of systemic metronidazole (MTZ) and amoxicillin (AMX) has not been shown to be effective in controlling the disease. These unfavorable results may have occurred due to the limitation in the change of the submucosal microbiological profile due to mechanical difficulties in the decontamination of the implant threads. Therefore, this randomized clinical trial (RCT) aimed to evaluate the clinical and microbiological (microbial complexes and changes in the diversity of the submucosal biofilm) effects of MTZ+AMX as adjuncts to anti-infectious surgical treatment plus Er:YAG in the treatment of peri-implantitis. Ninety-four subjects with untreated peri-implantitis are being included and will be randomly assigned to receive (i) open flap debridement plus Er:YAG irradiation alone (control), or (ii) with adjunctive systemically administered MTZ (400 mg) + AMX (500 mg) thrice a day (TID) for 14 days (test). Subjects will be monitored up to 12 months post-treatment. Submucosal biofilm samples from the deepest site of each implant with peri-implantitis will be collected in duplicate per patient: at baseline and at 3, 6 and 12 months post-therapy and analyzed by checkerboard DNA-DNA hybridization for 40 bacterial species, and at baseline, 3 and 12 months post-treatment for 16S rRNA sequencing (Ion Torrent PGM System). The primary outcome variable of this trial will be the difference between treatment groups for the change in CAL from baseline to 12 months. The significance of differences in each group (over the course of the study) will be sought using the Student's-t test; and among groups (at each time point) using either ANOVA /ANCOVA or Kruskal Wallis tests and post-hoc analyses, depending on normality of the data. Fisher's exact test will be used to compare differences in the frequency of gender. Statistical significance will be set at 5%.

Inclusion Criteria:

• 18-70 years of age;
• in general good health,
• at least one dental implant in function for at least one year with untreated peri-implantitis defined as: presence of bleeding and/or suppuration on gentle probing, probing depths (PD) ≥ 6mm, and bone levels ≥3mm apical of the most coronal portion of the intraosseous part of the implant.

Exclusion Criteria:

• subjects with ≥6 sites with PD ≥5mm;
• individuals that received periodontal treatment within three months prior to entering the study;
• inability to perform proper supramucosal and supragingival plaque control (e.g., due to improper restoration design or lack of skills);
• poorly adapted implant-supported restoration;
• diabetes;
• pregnancy;
• nursing;
• history of allergies to metronidazole and/or amoxicillin, or any other ingredient of oral care products;
• alcohol or drug abuse;
• any systemic diseases that could affect post-operative healing or that required antibiotic premedication for routine dental therapy;
• long-term use of mouthrinses;
• anti-inflammatory medications;
• any other drug that could interfere with the study outcomes within three months prior to entering the study;
• use of antibiotics within six months prior to entering the study.