Gut and mouth bacteria may predict who benefits from probiotics for gum disease

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Age between 45 and 65 years: Restricting eligibility to this age range reduces potential confounding from age-related comorbidities and ensures adequate natural dentition for standardized gingival crevicular fluid (GCF) sampling. 2. Diagnosis of Stage III periodontal disease (PD): Participants must have clinically confirmed Stage III (severe) PD according to the 2017 American Academy of Periodontology/European Federation of Periodontology (AAP/EFP) classification system to ensure consistent disease severity among enrolled participants. Exclusion Criteria: 1. Use of prebiotic, probiotic, or fiber supplements within the previous 6 months: Recent use of microbiome-modulating supplements could alter baseline oral or gut microbial composition and confound assessment of responsiveness to the probiotic intervention. 2. Use of antibiotics within the previous 6 months: Antibiotic exposure can cause sustained disruptions to host microbiomes and immune responses, which may confound evaluation of probiotic-related changes in inflammatory and microbial outcomes. 3. Systemic diseases affecting the periodontium (uncontrolled diabetes mellitus defined as HbA1c ≥8%, autoimmune diseases): These conditions may independently influence periodontal inflammation, immune responses, and microbiome composition, potentially confounding interpretation of study outcomes. 4. History of communicable or chronic diseases that may render study participation unsafe: Certain medical conditions may increase the risk of adverse events associated with study procedures or probiotic exposure. 5. Pregnancy or breastfeeding: Physiological changes during pregnancy and lactation may influence periodontal status, immune function, and microbiome composition. 6. Having fewer than 20 natural teeth: Adequate natural dentition is required to support standardized periodontal assessments and reliable biospecimen collection. 7. Use of removable dentures: Denture use alters the oral microbiome and local inflammatory environment and may compromise the validity of periodontal outcome measures. 8. Surgical periodontal disease treatment within the previous 6 months: Recent surgical intervention may induce substantial changes in the periodontal environment, complicating baseline measurement and interpretation of treatment response. 9. Ongoing participation in another clinical trial: Concurrent participation in another trial may introduce overlapping interventions or behavioral changes that could compromise internal validity. 10. Lack of mobility or physical independence: Physical limitations may make participation burdensome or interfere with attendance at study visits and completion of study procedures. 11. Inability to communicate orally or in written English: Because study procedures and consent materials will be conducted in English, adequate language proficiency is required to ensure participants understand study instructions and provide informed consent.