Lactobacillus reuteri is one of the most extensively researched probiotic strains for oral health. Specific strains — DSM 17938 and ATCC PTA 5289 — have been studied in over two dozen clinical trials for their potential effects on gingivitis, periodontitis, dental caries, and halitosis. The bacterium produces reuterin, a broad-spectrum antimicrobial compound that may selectively inhibit oral pathogens. While the evidence is promising, particularly for reducing gingival inflammation, results are best when combined with professional dental care and good oral hygiene.
If you have been researching oral probiotics, one bacterial name comes up more than almost any other: Lactobacillus reuteri. This species has been the subject of extensive clinical investigation for dental and periodontal applications, with specific strains showing measurable effects across several oral health conditions.
This article is a comprehensive review of the published research on L. reuteri for oral health — what the studies actually found, which strains were tested, and what practical conclusions you can draw.
What Is Lactobacillus reuteri?
Lactobacillus reuteri is a Gram-positive, rod-shaped bacterium that naturally inhabits the human gastrointestinal tract, including the oral cavity. It is one of the few Lactobacillus species that has been identified as a natural resident of the human mouth, which gives it a biological advantage in oral colonization compared to gut-adapted probiotics.
The species was first isolated from human breast milk and fecal samples in 1962 by Gerhard Reuter (who the species is named after). Since then, it has become one of the most studied probiotic organisms in the world, with applications ranging from infant colic to immune modulation.
The Key Oral Health Strains
Not all L. reuteri strains are equal. The two strains with the most oral health research are:
-
DSM 17938 — Originally isolated from a Peruvian mother's breast milk. This strain has been studied extensively for both gastrointestinal and oral applications. It is the successor to the widely studied strain ATCC 55730, which was cured of antibiotic resistance plasmids to create DSM 17938.
-
ATCC PTA 5289 — Isolated from the oral cavity of a healthy Japanese woman. This strain was specifically selected for its ability to adhere to oral epithelial cells and its production of antimicrobial compounds effective against oral pathogens.
Most clinical studies on oral health use a combination of both strains, typically delivered as dissolving lozenges.
Mechanism of Action: How L. reuteri Works in the Mouth
L. reuteri does not simply "crowd out" bad bacteria through competition for space. It has specific biochemical mechanisms that may contribute to oral health.
Reuterin Production
The signature antimicrobial compound produced by L. reuteri is reuterin (3-hydroxypropionaldehyde). Reuterin is produced when L. reuteri metabolizes glycerol, which is present in saliva and oral tissues. A 2008 study in BMC Microbiology demonstrated that reuterin has broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria, yeasts, fungi, and protozoa.
Crucially, reuterin appears to be more effective against certain pathogenic species than against commensal oral bacteria, suggesting a degree of selectivity. Research in Applied and Environmental Microbiology (2010) found that reuterin concentrations that inhibited Streptococcus mutans (a primary caries pathogen) had less effect on beneficial Streptococcus species.
Adhesion and Colonization
L. reuteri ATCC PTA 5289 was specifically selected for its adhesion properties. A 2012 study in PLOS ONE showed that this strain adhered effectively to human gingival epithelial cells and saliva-coated hydroxyapatite (a model for tooth surfaces), which is a prerequisite for sustained oral colonization.
Immune Modulation
Beyond direct antimicrobial effects, L. reuteri may modulate the local immune response. Research published in Infection and Immunity (2009) demonstrated that L. reuteri strains could reduce pro-inflammatory cytokine production (specifically TNF-alpha) from human monocytes stimulated by oral pathogens. This anti-inflammatory mechanism may be particularly relevant for gum disease, which is fundamentally an inflammatory condition.
Clinical Evidence: Gingivitis
Gingivitis — inflammation of the gums, typically caused by plaque accumulation — is one of the most studied applications for L. reuteri.
A 2009 randomized controlled trial published in the Journal of Clinical Periodontology by Twetman et al. examined the effects of L. reuteri lozenges (combining DSM 17938 and ATCC PTA 5289) in 59 patients with moderate to severe gingivitis. After 14 days, the probiotic group showed significant reductions in gingival bleeding index and plaque index compared to placebo.
A larger 2013 study in the same journal by Iniesta et al. investigated L. reuteri as an adjunct to professional cleaning in 40 patients with chronic gingivitis. At the 4-week follow-up, the probiotic group maintained lower gingival index scores and bleeding on probing compared to the placebo group.
A 2016 systematic review in the Journal of Clinical Periodontology by Martin-Cabezas et al. pooled data from multiple trials and found a consistent trend toward reduced gingival inflammation with L. reuteri supplementation, though the authors noted heterogeneity across studies and called for larger, longer-term trials.
Clinical Evidence: Periodontitis
Periodontitis — the more severe form of gum disease involving loss of bone and attachment tissue — represents a more challenging target for probiotic intervention. The evidence here is intriguing but still developing.
A pivotal 2013 study by Teughels et al. in the Journal of Clinical Periodontology investigated L. reuteri as an adjunct to scaling and root planing (SRP) in 30 chronic periodontitis patients. The probiotic group received lozenges containing L. reuteri DSM 17938 and ATCC PTA 5289 twice daily for 12 weeks following SRP. At the 12-week assessment, the probiotic group showed significantly greater reduction in probing pocket depth and greater clinical attachment gain compared to the SRP-plus-placebo group.
A 2018 study by Jorgensen et al. in the Journal of Periodontology replicated these findings in a larger cohort of 39 patients with chronic periodontitis, finding that L. reuteri adjunctive therapy resulted in improved periodontal clinical parameters at 3 and 6 months post-SRP.
However, not all studies have been positive. A 2017 trial by Galofre et al. in the Journal of Periodontal Research found no significant additional benefit of L. reuteri over SRP alone in 28 periodontitis patients at 12 weeks. The authors speculated that differences in patient populations, compliance, and disease severity may account for the discrepancy.
The overall picture suggests that L. reuteri may provide adjunctive benefits to professional periodontal treatment in some patients, but it is not a standalone treatment for periodontitis. If you have active periodontal disease, professional treatment from your dentist or periodontist remains essential.
Clinical Evidence: Dental Caries
The evidence for L. reuteri in cavity prevention centers primarily on its effects on Streptococcus mutans, the bacterium most strongly associated with tooth decay.
A 2005 study by Caglar et al. in Caries Research found that daily consumption of L. reuteri-containing yogurt significantly reduced salivary S. mutans counts compared to control yogurt over a 2-week period.
A 2014 study in the European Journal of Oral Sciences by Stensson et al. followed children from birth to age 9 whose mothers had taken L. reuteri during the last month of pregnancy and who themselves received the probiotic during their first year of life. The children in the probiotic group had significantly fewer caries at age 9 compared to the placebo group.
However, the relationship between reduced S. mutans counts and actual cavity prevention is not perfectly linear. A 2019 meta-analysis in BMC Oral Health noted that while probiotics consistently reduce S. mutans levels, the translation to clinical caries outcomes needs further long-term study.
Clinical Evidence: Halitosis (Bad Breath)
Bad breath is often caused by volatile sulfur compounds (VSCs) produced by anaerobic bacteria, primarily on the tongue dorsum. L. reuteri may address halitosis by reducing the populations of VSC-producing bacteria.
A 2012 study by Keller et al. in the European Journal of Clinical Microbiology & Infectious Diseases found that L. reuteri supplementation resulted in reductions in organoleptic (smell-based) halitosis scores in a group of 24 healthy volunteers after 1 week of use.
A 2019 systematic review in BMJ Open examined probiotic interventions for halitosis across multiple studies and concluded that probiotics, including L. reuteri, showed "short-term effects on reducing halitosis" but that "evidence remains limited and heterogeneous."
ProDentim
Oral Probiotic for Gum & Teeth Health
ProDentim includes Lactobacillus reuteri among its oral probiotic strains, delivered as a dissolving tablet that allows direct oral colonization — the format used in the clinical studies reviewed above.
We may earn a commission if you make a purchase through our links, at no extra cost to you.
Dosage and Format Recommendations
Based on the clinical literature, here is what the research supports:
Dosage
Most clinical trials used 1 x 10^8 CFU (100 million) of each strain per dose, taken twice daily. Some formulations combine both strains in a single lozenge at this dose. Higher doses have not been systematically compared, so it is unclear whether more is better.
Format
All positive oral health studies used dissolving lozenges or tablets — not capsules. This is non-negotiable for oral applications. The bacteria must be released directly into the oral cavity and have sustained contact time with oral tissues to colonize effectively. Swallowing a capsule containing L. reuteri may benefit the gut but will not deliver the oral effects seen in clinical studies.
Duration
- Gingivitis — Studies showed effects within 14 days to 4 weeks
- Periodontitis — As adjunctive therapy, 12 weeks of supplementation was typical
- Caries prevention — Longer-term supplementation (months to years) was used in preventive studies
- Halitosis — Short-term effects observed within 1-2 weeks
Timing
The studies generally instructed participants to use the lozenges after oral hygiene procedures (brushing and flossing). Taking the probiotic on a clean oral surface may improve adhesion and colonization. Evening use, after final brushing, provides the longest period without food or drink disturbance.
Safety Profile
L. reuteri has an excellent safety record. It has been granted GRAS (Generally Recognized as Safe) status by the U.S. FDA and QPS (Qualified Presumption of Safety) status by the European Food Safety Authority.
A 2019 systematic review of L. reuteri safety data across all clinical applications, published in Microbial Cell Factories, found no serious adverse events attributable to the probiotic across thousands of participants, including infants, children, adults, and elderly populations.
Mild side effects reported in some studies include temporary gastrointestinal symptoms (bloating, gas) that typically resolve within the first few days of use.
Individuals with compromised immune systems, those on immunosuppressive medications, or those with severe illness should consult their healthcare provider before taking any probiotic supplement.
Limitations of the Current Evidence
It is important to be honest about what we do not yet know:
- Most studies are small — Sample sizes of 20-60 participants are common. Large-scale, multi-center trials are still needed.
- Study durations are short — Most trials last 2-12 weeks. Long-term effects (years) of L. reuteri supplementation are not well characterized.
- Publication bias — Positive results are more likely to be published than negative ones, which may inflate perceived efficacy.
- Heterogeneity — Differences in patient populations, disease severity, oral hygiene habits, and outcome measures make it difficult to directly compare studies.
- Mechanism clarity — While reuterin production, adhesion, and immune modulation are established, the relative contribution of each mechanism to clinical outcomes is not fully understood.
Practical Takeaways
Based on the current body of evidence, here is a reasonable interpretation:
- L. reuteri is among the best-supported oral probiotic strains, with clinical evidence across multiple oral health conditions.
- It is an adjunct, not a replacement for brushing, flossing, and professional dental care. Consult your dentist about incorporating it into your oral care routine.
- Strain and format matter — Look for products containing DSM 17938 and/or ATCC PTA 5289 in a dissolving tablet or lozenge format.
- Expectations should be calibrated — The effects are statistically significant but moderate. L. reuteri may help tip the microbial balance in a favorable direction, particularly alongside professional treatment.
- Safety is well-established — For most healthy adults, L. reuteri supplementation carries minimal risk.
ProDentim
Oral Probiotic for Gum & Teeth Health
If you are interested in trying an L. reuteri-containing oral probiotic, ProDentim delivers this and other research-backed strains in the dissolving tablet format that clinical studies have used.
We may earn a commission if you make a purchase through our links, at no extra cost to you.
