Characterization of Small Intestinal Bacterial Overgrowth and Intestinal Barrier-Related Biomarkers in Patients With Severe Periodontitis: A Pilot Prospective Longitudinal Observational Cohort Study

Inclusion Criteria: * Adults aged ≥18 years. * Diagnosis of Stage III/IV periodontitis, Grade B or C, according to the applicable periodontal classification criteria. * Presence of sufficient dentition to permit a meaningful full-mouth periodontal examination. * Ability and willingness to perform the breath test and provide blood samples and questionnaire data. * Written informed consent. * Patients with stable chronic systemic conditions may be included, provided that the condition is clinically controlled and does not meet any exclusion criterion. Relevant systemic diseases and concomitant medications will be recorded and considered as potential confounding factors. Exclusion Criteria: * Uncontrolled or severe systemic disease likely to substantially affect periodontal inflammation, intestinal microbiota, intestinal barrier function, systemic inflammatory status, or the safety of periodontal treatment. * Antibiotic, systemic antifungal, or probiotic therapy within the preceding 4 weeks. * Recent periodontal treatment that could materially influence baseline periodontal or biological measurements. * Diagnosed inflammatory bowel disease, celiac disease, major intestinal surgery, or another major gastrointestinal condition that would substantially interfere with interpretation of SIBO or intestinal barrier-related outcomes. * Current pregnancy or breastfeeding. * Other condition or treatment judged by the investigator to materially interfere with the study outcomes or procedures.