This randomized, double-blind, crossover clinical trial evaluated the effect of a probiotic-containing nanofiber dental floss on subgingival red complex periopathogens and gingival health in periodontally healthy individuals. Thirty male participants underwent two 14-day flossing interventions (probiotic floss and placebo floss), separated by a 14-day washout period. Clinical and microbiological parameters were assessed using standardized indices and multiplex qPCR.

This study was conducted prospectively but is being registered retrospectively to ensure transparency and compliance with NIH guidelines.

The study aimed to validate a targeted subgingival delivery method using Ligilactobacillus salivarius-infused nanofiber floss. Participants received both floss types in a crossover design. Clinical parameters (Approximal Plaque Index and Sulcus Bleeding Index) and microbiological markers (presence of L. salivarius, red complex pathogens, total bacterial DNA) were measured at multiple timepoints. DNA analysis was performed using validated multiplex qPCR protocols. Statistical analysis included non-parametric tests and correlation models. The study was ethically approved and conducted prospectively, but is being registered retrospectively to ensure transparency and support future publication.

Retrospective Registration Note:

This study was originally designed as a method validation investigation to refine subgingival probiotic delivery techniques using a newly developed nanofibre dental floss containing Ligilactobacillus salivarius. At the time of ethics approval and initiation (February 2022), the study was not classified as a clinical trial. However, subsequent interpretation of NIH guidelines suggests that the randomized, blinded, crossover design involving a health-related behavioral intervention meets criteria for interventional clinical research. Accordingly, the investigators now recognize that the study should be registered as a clinical trial. The research team is submitting this retrospective registration to ensure transparency and support future publication. No participant-level outcomes have been modified post hoc, and all data were collected prospectively under full ethical oversight.

Inclusion Criteria:

• Male adults (≥18 years) of Czech or Slovak nationality
• ≥20 own teeth
• Good oral hygiene
• Maximum Stage 2 periodontitis

Exclusion Criteria:

• Immunocompromised status
• Systemic illness
• Antibiotic use within 2 months
• Smoking
• Probiotic use during study

Not discussed with the full team

Masking in this study was double-blind. Both participants and investigators were unaware of which type of dental floss-probiotic nanofiber floss or placebo floss-was being used during each phase of the trial. This design was implemented to minimize bias in participant behavior and outcome assessment, ensuring objective evaluation of clinical indices and microbiological results.