Peri-implantitis is an inflammatory disease affecting the tissues around dental implants and may lead to progressive bone loss and implant failure. Current diagnosis is mainly based on clinical and radiographic findings, which may not fully reflect the underlying inflammatory activity. Therefore, there is a need for biological markers that may provide additional information about disease-related changes.

This observational study aims to compare the levels of Meteorin-like protein (Metrnl) and selected inflammatory cytokines in peri-implant crevicular fluid obtained from individuals with peri-implantitis and individuals with healthy implants. The study will evaluate Metrnl, interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and interleukin-10 (IL-10). It will also examine the relationships between Metrnl and these inflammatory markers.

The study hypothesis is that Metrnl levels differ between healthy peri-implant tissues and peri-implantitis and are associated with pro-inflammatory and anti-inflammatory cytokine levels. The findings may help clarify the possible role of Metrnl in peri-implant inflammation and its potential as a biomarker for distinguishing peri-implant health from peri-implantitis.

Peri-implantitis is a biofilm-associated inflammatory disease characterized by inflammation of the peri-implant mucosa and progressive loss of supporting bone. Although clinical and radiographic parameters, including probing depth, bleeding on probing, suppuration, and radiographic bone loss, are central to diagnosis, these measures primarily reflect established tissue changes and may not fully characterize the underlying local immune-inflammatory response. Analysis of biomarkers in peri-implant crevicular fluid may therefore provide complementary information about the biological processes associated with peri-implant health and disease.

Meteorin-like protein (Metrnl) is an immunoregulatory protein involved in inflammatory regulation, macrophage polarization, and tissue repair. Experimental and clinical evidence suggests that Metrnl may interact with both pro-inflammatory and anti-inflammatory pathways. However, its possible role in peri-implantitis has not been sufficiently investigated.

This observational study will include individuals with peri-implantitis and individuals with healthy peri-implant tissues. Participants will be classified according to clinical and radiographic findings. Clinical periodontal and peri-implant parameters will be recorded to characterize the study groups. Peri-implant crevicular fluid samples will be collected from selected implant sites, and the concentrations of Metrnl, interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and interleukin-10 (IL-10) will be analyzed.

The primary objective is to compare Metrnl levels between the peri-implantitis and peri-implant health groups. Secondary objectives are to compare IL-1β, TNF-α, and IL-10 levels between the groups and to evaluate the relationships between Metrnl and these pro-inflammatory and anti-inflammatory cytokines. The study will also explore the ability of Metrnl and the evaluated cytokines to distinguish peri-implant health from peri-implantitis.

The study hypothesis is that Metrnl levels differ between peri-implant health and peri-implantitis and are associated with the local inflammatory cytokine profile. Evaluation of these relationships may provide new information about the role of Metrnl in the immunoinflammatory mechanisms of peri-implantitis and its potential value as a biomarker.

Inclusion Criteria:

• Individuals aged 18 years or older
• Individuals without systemic disease
• Individuals with at least one healthy implant or one implant affected by peri-implantitis
• At least 1 year having elapsed since placement of the prosthetic restoration on the relevant implant

Exclusion Criteria:

• Pregnant or lactating individuals.
• Current smokers.
• Use of antibiotics or corticosteroids within the previous 6 months.
• Presence of an implant-supported removable prosthesis.
• Periodontal or peri-implant treatment within the previous 6 months.

The study population will consist of adults with at least one functioning dental implant who are evaluated at the Department of Periodontology, Faculty of Dentistry, Atatürk University. Participants will be classified into two groups according to clinical and radiographic findings: individuals with peri-implantitis and individuals with peri-implant health. Peri-implant clinical parameters and peri-implant crevicular fluid biomarker levels will be evaluated and compared between the groups.

The plan to share individual participant data has not yet been determined and will be considered after study completion and publication of the main results.