The primary objective of this study is to evaluate the change in probing depth in patients with peri-implantitis, assessing the influence of systemic antibiotic (azithromycin) adjunctive to non-surgical treatment at 12 months. The secondary objective is to assess clinical, radiographic, microbiological, and systemic changes at 3, 6, and 12 months.

This study is designed as a placebo-controlled, randomized, triple-blind clinical trial in subjects diagnosed with peri-implantitis.

The treatment will consist of debridement of the implant surface and curettage of the pocket epithelium. The control group will receive placebo (1 placebo tablet per day for 3 days), and the test group will receive systemic azithromycin 500 mg per day for 3 days (1 tablet of 500 mg azithromycin per day for 3 days).

Peri-implantitis is defined as the pathological alteration associated with plaque that occurs in the tissues surrounding dental implants, characterized by inflammation of the peri-implant mucosa and subsequent progressive loss of supporting bone. Bacterial colonization of the implant surface in a susceptible subject is considered the primary etiological factor of this pathology. Case series and clinical trials have demonstrated an additional benefit when using systemic antibiotics such as ornidazole or metronidazole after non-surgical treatment of peri-implantitis.

The rationale for conducting this clinical trial lies in the lack of randomized studies that have tested the non-surgical treatment of peri-implantitis with shorter antibiotic regimens and their potential impact on systemic health.

The primary objective of this randomized clinical trial is to evaluate the change in probing depth at 12 months in patients with peri-implantitis, assessing the influence of systemic antibiotic (azithromycin) as an adjunct to the non-surgical treatment of peri-implantitis.

The secondary objective is to assess clinical, radiographic, and microbiological changes at 3, 6, and 12 months. Additionally, systemic biomarkers, complete blood count, glycosylated hemoglobin and creatinine will be evaluated at day 7, and 3, 6, and 12 months. Endothelial function (endothelium-dependent vasodilation measured in the brachial artery) and subclinical atherosclerosis (measurement of carotid artery intima-media thickness) will be evaluated at 12 months.

Design: This research is designed as a 1-year randomized controlled trial (RCT), with 2 parallel groups, triple-blind, and placebo-controlled.

Population: Patients who come to the Periodontology Department, Faculty of Dentistry, University of Santiago de Compostela with dental implants presenting pathology.

Treatment Groups: Study group: patients treated by non-surgical treatment in conjunction with systemic azithromycin. Control group: patients treated by non-surgical treatment in conjunction with a placebo. Subjects will be randomly assigned to one of the two treatment groups.

Randomization: A balanced randomization by blocks will be performed to avoid imbalances between the two treatment groups. The randomization outcome will be stored in envelopes along with the antibiotic or placebo containers that will be delivered on the day of the non-surgical treatment.

Treatment: After the diagnosis of peri-implantitis, patients were instructed in oral hygiene and motivation was reinforced. After that, one session of nonsurgical treatment consisting of supra- and submucosal mechanical debridement using ultrasound with a metal periodontal tip was performed with concomitant irrigation of chlorhexidine of 0.12%. The tip removed granulation tissue and also touched the implant surface. After that, a steel curette Columbia 4R/4L was used to remove granulation tissue and minor mucosa curettage. If oral hygiene was not allowed by prosthetic design, a contour correction was made. Immediately after treatment, patients were prescribed to apply a chlorhexidine gel in the area 2 times a day for 2 weeks and depending on the result of randomization, the exact number of antibiotic or placebo tablets to be taken by the patient in the following days will be provided.

Inclusion Criteria:

• older than 18 years;
• absence of systemic pathology contraindicating treatment;
• presence of at least 1 implant diagnosed with peri-implantitis: presence of bleeding on probing, probing depth ≥6 mm, and radiographic bone level ≥3 mm apical to the most coronal portion of the intraosseous part of the implant;
• absence of implant mobility;
• patients without periodontitis or with treated periodontitis;
• patients who understand the treatment and are willing to comply with it by providing written informed consent.

Exclusion Criteria:

• smokers ≥10 cigarettes/day;
• diabetic patients (HbA1c level ≥6,5%);
• pregnant or breastfeeding women;
• use of antibiotics, corticosteroids, and/or immunosuppressive treatment in the 3 months prior to the start of the study;
• allergy to azithromycin;
• patients with a history of bisphosphonate treatment;
• chronic consumption of non-steroidal anti-inflammatory drugs;
• bone loss exceeding the apex of the implant;
• prosthesis that does not allow access to peri-implantitis treatment