The goal of this observational study is to explore the comorbid association between periodontitis and chronic kidney disease (CKD) based on the oral-renal axis in adults aged 18 to 75 years. The main question it aims to answer is:

Is periodontitis associated with chronic kidney disease through oral-renal axis-related mechanisms?

Participants aged 18 to 75 years will be recruited and undergo clinical assessment, sample collection, and laboratory testing as part of the study. Periodontal status, kidney function, and oral microbiota characteristics will be evaluated to investigate the association between periodontitis and CKD. Fecal samples will also be collected for exploratory analysis of gut microbiota to assess its potential relevance to the oral-renal relationship.

This observational case-control study with a cross-sectional design aims to investigate the association between periodontitis and chronic kidney disease in adults aged 18 to 75 years. Participants will be classified into four groups according to the presence or absence of periodontitis and chronic kidney disease: PD(+)/CKD(-), PD(+)/CKD(+), PD(-)/CKD(+), and PD(-)/CKD(-). Periodontal examination, renal function assessment, and biospecimen collection will be performed. Oral samples will be analyzed to characterize oral microbiota, and fecal samples will be collected for exploratory gut microbiota analysis. The study aims to explore the oral-renal association and the potential relevance of gut microbiota to this relationship.

Inclusion Criteria Disease Group: 1. Adults aged 18 to 75 years; 2. No restrictions on sex or race; 3. Diagnosis of at least one target disease, including periodontitis or chronic kidney disease; 4. Ability and willingness to provide written informed consent; 5. Ability to understand the study procedures and comply with study requirements.

Control Group: 1. Adults aged 18 to 75 years; 2. No restrictions on sex or race; 3. No history of diagnosis of periodontitis or chronic kidney disease; 4. Ability and willingness to provide written informed consent; 5. Ability to understand the study procedures and comply with study requirements.

Exclusion Criteria

1. Age <18 years or >75 years; 2. Pregnancy or lactation; 3. Current smoking, alcohol abuse, or betel nut chewing; 4. Unhealthy dietary habits, such as frequent intake of high-salt or high-fat foods; 5. Use of antibiotics or probiotics, or receipt of oral/gastrointestinal surgery, within the past 2 months; 6. Fewer than 8 natural teeth remaining; 7. Severe systemic diseases other than the target condition, mental illness, or other conditions that may affect study participation, compliance, or data interpretation; 8. Inability to understand the study procedures; 9. Current participation in another clinical trial.

Adults aged 18 to 75 years will be recruited from the College of Stomatology, Xi'an Jiaotong University. The study population will include participants with periodontitis and/or chronic kidney disease, as well as healthy controls without a history of periodontitis or chronic kidney disease. All participants must be able to provide written informed consent and comply with study procedures.