This observational cross-sectional study will evaluate salivary apelin, chemerin, ghrelin, and lipocalin-2 levels in individuals with different periodontal and systemic conditions. Participants will be divided into four groups according to periodontal status and the presence or absence of type 2 diabetes mellitus.

Clinical periodontal measurements and unstimulated saliva samples will be obtained before periodontal treatment. Salivary biomarker levels will be measured using enzyme-linked immunosorbent assay kits. The study aims to determine whether salivary apelin, chemerin, ghrelin, and lipocalin-2 levels are associated with periodontitis, type 2 diabetes mellitus, and periodontal clinical parameters.

This observational cross-sectional study will be conducted at the Department of Periodontology, Faculty of Dentistry, Necmettin Erbakan University. The study will include individuals who apply to the periodontology clinic for various reasons, meet the eligibility criteria, and agree to participate by signing the informed consent form.

The study population will consist of 88 individuals aged 18-80 years. Participants will be allocated into four groups according to periodontal status and the presence or absence of type 2 diabetes mellitus: periodontally healthy and systemically healthy individuals, periodontally healthy individuals with type 2 diabetes mellitus, systemically healthy individuals with periodontitis, and individuals with both periodontitis and type 2 diabetes mellitus. Each group will include 22 participants.

Periodontal status will be determined by a calibrated specialist clinician based on clinical and radiographic examinations according to the 2017 World Workshop Classification of Periodontal and Peri-Implant Diseases and Conditions. Participants in the periodontitis groups will be required to meet the criteria for generalized Stage II or Stage III periodontitis. Periodontal clinical parameters, including probing depth, clinical attachment loss, bleeding on probing, gingival index, plaque index, gingival recession, tooth mobility, furcation involvement, and keratinized gingival width, will be recorded from six sites per tooth. Sociodemographic data, oral hygiene habits, and body mass index will also be recorded.

Unstimulated saliva samples will be collected before periodontal probing and before periodontal treatment in order to prevent possible contamination of saliva by bleeding during clinical measurements. Participants will be instructed not to brush their teeth and to avoid food, chewing gum, cosmetic products such as lipstick, and medications that may affect salivary measurements for at least one hour before sample collection. Saliva samples will be collected between 8:00 AM and 10:00 AM. After rinsing the mouth with water, saliva will be collected into plastic tubes using a glass funnel within five minutes. The samples will then be centrifuged at 1000 rpm for 10 minutes to remove cellular debris and plaque. The supernatant will be transferred into polypropylene Eppendorf tubes without disturbing the pellet and stored at -20°C until analysis.

On the day of analysis, samples will be thawed at +4°C. Salivary chemerin, ghrelin, apelin, and lipocalin-2 levels will be measured using enzyme-linked immunosorbent assay kits according to the manufacturer's instructions.

The primary objective of the study is to compare salivary apelin, chemerin, ghrelin, and lipocalin-2 levels among individuals with different periodontal and systemic conditions. Secondary objectives include evaluating the relationships between salivary biomarker levels and clinical periodontal parameters and assessing the diagnostic performance of these biomarkers in distinguishing periodontitis from periodontal health.

Statistical analysis will be performed using IBM SPSS Statistics software. Continuous data will be expressed as mean and standard deviation. The normality of data distribution will be assessed using the Kolmogorov-Smirnov test. Between-group comparisons will be performed using appropriate parametric or non-parametric tests according to data distribution. Correlations between clinical and biochemical parameters will be evaluated. Receiver operating characteristic curve analysis will be used to assess the sensitivity and specificity of salivary biomarkers for distinguishing periodontitis from periodontal health. A p-value of less than 0.05 will be considered statistically significant.

Inclusion Criteria:

• Individuals aged 18 to 80 years. Individuals who apply to the Department of Periodontology, Faculty of Dentistry, Necmettin Erbakan University.

Individuals who agree to participate in the study and sign the informed consent form.

Presence of at least 20 teeth. For the periodontally healthy groups: diagnosis of periodontal health based on routine clinical and radiographic examination.

For the periodontitis groups: diagnosis of generalized Stage II or Stage III periodontitis based on routine clinical and radiographic examination according to the 2017 World Workshop Classification of Periodontal and Peri-Implant Diseases and Conditions.

For the type 2 diabetes mellitus groups: diagnosis of type 2 diabetes mellitus. For the systemically healthy groups: absence of systemic diseases, including type 2 diabetes mellitus.

Exclusion Criteria:

• Periodontal treatment, including scaling and root surface debridement, within the last 6 months.

Antibiotic use within the last 6 months. Pregnancy or lactation. Presence of autoimmune diseases such as rheumatoid arthritis, familial Mediterranean fever, ankylosing spondylitis, Behçet disease, or psoriasis.

Presence of systemic diseases other than type 2 diabetes mellitus in the diabetes groups.

Presence of systemic diseases such as nephrotic syndrome, chronic renal disease, or cardiovascular disease.

Smoking 10 or more cigarettes per day.

The study population will consist of individuals aged 18 to 80 years who apply to the Department of Periodontology, Faculty of Dentistry, Necmettin Erbakan University, meet the eligibility criteria, and agree to participate. Participants will be categorized into four groups according to periodontal status and the presence or absence of type 2 diabetes mellitus: periodontally healthy systemically healthy individuals, periodontally healthy individuals with type 2 diabetes mellitus, systemically healthy individuals with periodontitis, and individuals with both periodontitis and type 2 diabetes mellitus.