Best-studied oral probiotic strains
The most frequently studied oral probiotic for gum health is a combination of two Lactobacillus reuteri strains, DSM 17938 and ATCC PTA 5289, used in 17 of 36 trials in one review. Other strains with randomised trials include Streptococcus salivarius M18 and Bifidobacterium animalis subsp. lactis HN019, usually as lozenges. “Best-studied” does not mean proven: pooled evidence for gingivitis is not statistically clear, and results do not transfer between strains.
This article answers one question. For what Probiotics is, where it comes from and its other uses, see the Probiotics ingredient guide.
Key findings
- L. reuteri DSM 17938 + ATCC PTA 5289 is the most-studied oral combination.
- S. salivarius M18 and B. lactis HN019 have been tested in lozenge trials.
- Effects are strain-specific; a species name alone is not enough.
- Pooled gingivitis evidence is inconsistent; periodontitis adjunct evidence is more favourable.
The strains and how they were tested
| Strain | How it was studied | Format and dose | What to note |
|---|---|---|---|
| L. reuteri DSM 17938 + ATCC PTA 5289 | Used in 17 of 36 RCTs in a 2021 review of gingivitis and periodontitis | Mostly lozenges or tablets | Most-studied; results vary by trial |
| S. salivarius M18 | 62 people with gingivitis, 3 months plus washout | Lozenges, ≥5×10⁸ CFU each | Reported reduced gingival bleeding and plaque |
| B. animalis subsp. lactis HN019 | 60 patients after professional cleaning, 8 weeks | Lozenges twice daily | Adjunct design |
| L. rhamnosus GG + B. lactis BB-12 | Lozenge trial in healthy adults | Lozenges | Measured plaque, gingival inflammation and microbiome |
What pooled evidence says
A 2021 meta-analysis of 11 trials (554 patients) found no significant improvement in gingival index, plaque or bleeding in plaque-induced gingivitis (2021 meta-analysis). A 2025 meta-analysis of 24 trials found non-significant differences in gingivitis but lower plaque index when probiotics were added to periodontitis treatment (2025 meta-analysis). See the oral probiotics evidence review.
Evidence table
| Study or source | Population | What was tested | Main result | Limitations |
|---|---|---|---|---|
| Frontiers review, 2021 | 36 RCTs | Various oral probiotics | L. reuteri DSM 17938 + ATCC PTA 5289 used in 17 trials | Narrative review |
| S. salivarius M18 RCT | 62 people with gingivitis | Lozenges ≥5×10⁸ CFU, 3 months | Reduced gingival bleeding and plaque (per trial report) | Single strain, single trial |
| B. lactis HN019 RCT | 60 patients with gingivitis | Lozenges twice daily, 8 weeks, after cleaning | Evaluated as adjunct | Adjunct design |
| 2021 meta-analysis | 11 RCTs; 554 patients | Various strains | No significant gingivitis improvement | Heterogeneous |
| 2025 meta-analysis | 24 RCTs | Various strains, often adjunct | Gingivitis non-significant; periodontitis lower plaque | Heterogeneous |
Why format matters
Most oral-health trials used lozenges or tablets that dissolve in the mouth, keeping bacteria in contact with teeth and gums. Swallowed capsules are a different delivery method and have not been shown to act the same way.
Safety
- Generally well tolerated in trials.
- People who are immunocompromised or seriously ill should ask a clinician before using probiotics.
- Check chewables and lozenges for sugars or acids if you have enamel erosion.
Limitations
- Small, short trials with varied outcomes.
- Adjunct designs make it hard to isolate probiotic effects.
- Commercial products may list species without strain designations.
Label checks
- Full strain designation (letters and numbers after the species name).
- CFU per serving, ideally guaranteed at expiry.
- Format: lozenge, chewable or capsule.
- Whether strains match those studied.
Related: dental health supplements comparison · probiotics guide
Frequently asked questions
Which oral probiotic strain is most studied?
A combination of Lactobacillus reuteri DSM 17938 and ATCC PTA 5289.
Does S. salivarius M18 work?
A 3-month lozenge trial in 62 people reported reduced bleeding and plaque; it is one trial.
Are oral probiotic capsules as good as lozenges?
Most trials used lozenges or tablets held in the mouth; capsules are a different delivery method.
Why do strain numbers matter?
Probiotic effects are strain-specific; the same species can behave differently.
Can probiotics replace dental cleaning?
No. Much of the favourable evidence comes from use alongside professional treatment.
References
- Probiotics in the management of gingivitis and periodontitis: a review. Front Dent Med. 2021.
- A three-month probiotic (S. salivarius M18) supplementation decreases gingival bleeding and plaque accumulation: RCT. PMC11276176.
- Effects of oral administration of B. animalis subsp. lactis HN019 on plaque-induced generalized gingivitis. PMC9614197.
- Effect of probiotics on gingival inflammation and oral microbiota: a meta-analysis. 2021. PMID 33772970
- Clinical effects of probiotics on gingivitis and periodontitis: systematic review and meta-analysis. BMC Oral Health. 2025. PMID 40186219