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.