Periodontitis is a prevalent chronic inflammatory disease driven by a dysbiotic oral biofilm and a dysregulated host immune response. Standard non-surgical periodontal therapy (NSPT) is primarily mechanical and, in selected cases, may be accompanied by antiseptics or systemic antibiotics. Targeted modulation of the oral microbiome ("microbiome engineering") is currently not part of routine periodontal care due to limited high-quality evidence.

PROPARO is a single-center, randomized, controlled pilot study designed to assess whether adjunctive oral supplementation with a probiotic containing Limosilactobacillus reuteri (commercial dietary supplement lozenge) alone or combined with vitamin B12 (commercial dietary supplement drops) is associated with changes in supragingival and subgingival oral microbiome composition during guideline-concordant NSPT compared with standard care alone. Participants with Stage III or IV periodontitis will be randomized 1:1:1 to: (1) NSPT/SPT without supplementation (control), (2) NSPT/SPT plus probiotic lozenges for 3 months, or (3) NSPT/SPT plus probiotic lozenges and vitamin B12 drops for 3 months.

The primary outcome is change in oral microbiome composition and structure (supragingival and subgingival), assessed using 16S rDNA-based profiling and metagenomic sequencing approaches. Secondary outcomes include clinical periodontal parameters (e.g., probing depth, clinical attachment level, bleeding on probing), oral hygiene/gingival indices, dental status, and participant-level ecological covariates (diet quality, perceived stress, physical activity). Sampling and assessments are aligned with routine care time points from baseline through supportive periodontal therapy follow-up (up to 12 months). This pilot trial aims to generate feasibility and effect-size estimates to inform future confirmatory studies and potential translation into guideline-based periodontal care.

Background and rationale:

Periodontitis is a chronic inflammatory disease characterized by periodontal pocketing, bleeding on probing, and progressive loss of periodontal supporting tissues, potentially resulting in tooth loss and impaired oral function. The disease is initiated and sustained by a dysbiotic biofilm in combination with an exaggerated or dysregulated host response. Current guideline-concordant non-surgical periodontal therapy (NSPT) targets biofilm removal by mechanical debridement and risk-factor control. Although antiseptics or systemic antibiotics may be used in selected indications, routine, targeted manipulation of the oral microbiome is not established because available evidence is heterogeneous and mechanistic data on whole-community changes remain limited.

Probiotics are live microorganisms that may confer health benefits when administered in adequate amounts. In periodontitis, adjunctive probiotic approaches-especially involving Limosilactobacillus reuteri-have been associated in some studies with improved clinical outcomes and/or reductions in selected periodontal pathogens. Prebiotics are substrates selectively utilized by microorganisms that may provide a growth or functional advantage. Vitamin B12 has been discussed as a potentially supportive factor for specific bacterial metabolic functions. However, the combined adjunctive use of a probiotic and a prebiotic-acting supplement within NSPT has not been comprehensively evaluated using community-level oral microbiome endpoints (supragingival and subgingival) in a controlled clinical setting.

Study objective:

The main objective of PROPARO is to assess whether adjunctive oral supplementation with a probiotic containing L. reuteri-alone or combined with vitamin B12-modifies the composition and structure of the oral microbiome (supragingival and subgingival) during NSPT and follow-up supportive periodontal therapy (SPT), compared with NSPT/SPT alone.

Study design:

PROPARO is a single-center, randomized, controlled pilot study with three parallel arms (allocation 1:1:1). The trial is designed as a feasibility and hypothesis-generating study. Clinical outcome assessment is intended to be single-blinded (outcome assessor) where operationally feasible; participant blinding is not possible due to distinguishable dosage forms and the absence of placebo.

Setting:

Recruitment and study procedures are conducted at Heidelberg University Hospital, Department of Conservative Dentistry (Poliklinik für Zahnerhaltungskunde), within routine periodontal care workflows.

Participants:

Adults (≥18 years) with diagnosed localized or generalized periodontitis, Stage III or IV, scheduled for NSPT are eligible. Key exclusions include pregnancy or breastfeeding; recent antibiotic use; recent use of pre-/probiotic supplements; recent subgingival instrumentation; conditions or medications expected to substantially confound oral microbiome composition or periodontal healing (e.g., relevant systemic immunosuppression); and other protocol-defined factors that may impair safety, consent validity, or interpretability of microbiome outcomes.

Interventions:

All participants receive guideline-concordant NSPT and follow-up supportive periodontal therapy (SPT/UPT), including oral hygiene instruction and professional care as per standard practice.

Arm 1 (Control): NSPT/SPT without supplementation. Arm 2 (Test A - Probiotic): NSPT/SPT plus a commercially available probiotic lozenge containing L. reuteri (dietary supplement; GUM® PerioBalance®, Sunstar Deutschland GmbH, Schönau, Germany), taken according to manufacturer instructions for 3 months starting with NSPT.

Arm 3 (Test B - Probiotic + Vitamin B12): NSPT/SPT plus the same probiotic regimen and commercially available vitamin B12 drops (dietary supplement; natural elements GmbH, Düsseldorf, Germany), administered according to manufacturer instructions for 3 months.

Concomitant care is standardized as far as feasible within routine practice (e.g., standardized toothpaste provided for home use). Participants are asked to avoid additional antimicrobial adjuncts (e.g., antiseptic mouthrinses) unless clinically required; any such use is documented.

Outcome measures:

Primary outcome: Oral microbiome composition and structure (supragingival and subgingival), including community-level measures (e.g., diversity metrics and community dissimilarity) and relative abundance profiles of microbial taxa/features. Microbiome profiling will be performed using 16S rDNA-based methods, with metagenomic sequencing approaches used to provide higher-resolution taxonomic and functional information where applicable.

Secondary outcomes: Periodontal clinical parameters (e.g., probing depth, clinical attachment level, bleeding on probing), additional oral indices (e.g., plaque control and gingival bleeding indices), dental status (DMFT), and participant-level ecological covariates that may influence microbiome composition (diet quality, perceived stress, physical activity). Demographic and socioeconomic information is collected to contextualize analyses and feasibility.

Timing of assessments and sampling:

Clinical assessments, questionnaires, and biospecimen collection (supragingival plaque, subgingival plaque, and unstimulated saliva) are obtained at standardized time points aligned with routine care: baseline and NSPT-related visits, re-evaluation/first SPT visit (~3 months), and subsequent SPT follow-up visits (up to ~12 months). The study is designed to minimize burden and avoid procedures beyond standard clinical practice, focusing on documentation and analysis of microbiological and clinical parameters during standard care.

Sample size:

This is a pilot study; robust effect-size estimates for the primary microbiome endpoints under the specific combined supplementation strategy are not available. Therefore, formal power calculation is not feasible. A total of 60 participants (20 per arm) is planned to assess feasibility (recruitment, adherence, completeness of sampling) and to generate preliminary effect-size estimates to inform a future confirmatory trial.

Randomization and allocation concealment:

Participants are randomized using stratified block randomization to support balanced group allocation (e.g., by sex, age category, and periodontitis diagnosis category). Allocation procedures are implemented to maintain concealment from outcome assessors where feasible.

Statistical considerations (high-level):

Primary analyses will compare microbiome changes over time between study arms using community-level metrics (alpha diversity, beta diversity) and appropriate multivariable models to estimate group and time effects while accounting for relevant covariates (e.g., smoking status, diet quality, perceived stress, physical activity). Differential abundance approaches may be used to identify taxa/features associated with intervention arms, with attention to multiple testing control where appropriate. Secondary outcomes will be summarized descriptively and explored longitudinally using suitable models for repeated measures. As a pilot study, analyses are intended to be exploratory and to inform future hypothesis testing.

Safety monitoring:

The supplements used are marketed as dietary supplements in Germany. Participants are monitored for adverse events and serious adverse events throughout participation. Any suspected supplement-related intolerance or clinically relevant events are documented and managed according to clinical judgment and institutional procedures.

Ethics and dissemination:

The study is conducted in accordance with the Declaration of Helsinki and applicable data protection requirements. Ethics approval is obtained from the Ethics Committee of the Heidelberg Medical Faculty prior to recruitment. All participants provide written informed consent. Data are pseudonymized and stored securely according to institutional policy. Results will be disseminated through peer-reviewed publication and scientific presentations, with prospective trial registration and prespecified primary outcomes to support transparency.

Inclusion Criteria:

• Age ≥ 18 years

  • Stage III or IV periodontitis (localized or generalized)
  • Ability to provide informed consent
  • Written informed consent including data protection consent

Exclusion Criteria:

• • Pregnancy or breastfeeding

  • Conditions/medications likely to substantially confound the oral microbiome or periodontal healing (e.g., uncontrolled diabetes mellitus, systemic immunosuppression, chronic steroid use)
  • Antibiotic use within the last 3 months
  • Use of oral pre-/probiotic supplements within the last 3 months
  • Recent subgingival instrumentation within the last 6 months
  • Need for obligatory adjunctive systemic antibiotic prophylaxis/therapy for NSPT
  • Severe active systemic infection or other conditions judged by investigators to pose undue risk
  • Regular use of antiseptic mouthrinses during the study period (unless medically required)
  • Strict diets likely to substantially alter baseline microbiome trajectories (e.g., ketogenic, strict vegan) per protocol definition
  • Chronic bowel diseases (for systemic confounding considerations)

De-identified individual participant data underlying the results reported in the primary publication (including key clinical outcomes and processed microbiome feature tables) will be made available upon reasonable request, subject to approval by the study team, a data use agreement, and applicable ethics and data protection requirements. Raw sequencing files and linkage keys will not be shared.

Beginning 6 months after publication of the primary results and ending 5 years thereafter.

Requests should include a brief proposal, analysis plan, and evidence of appropriate ethical approval (if required). Data will be provided to qualified researchers for non-commercial scientific purposes under a signed data use agreement. Contact: Diana.wolff@med.uni-heidelberg.de