658661030 © coolgraphic | gettyimages.com
Getty Images 658661030 Thumb 641b6596e9b72

Understanding probiotics and the oral-gut axis: It's a gut feeling

April 13, 2023
As research on the oral-gut axis advances, dental pros must understand the delicate balance of oral microorganisms and their role in immune function, as well as target pathogenic oral bacteria oral-systemically.

It is well understood that the entrance to the gastrointestinal tract begins within the oral cavity. Through the mechanical action of chewing and the chemical action of saliva’s role in early digestion, food products begin their digestive journey among the teeth, soft tissue, and biofilm within the oral cavity.

Countless studies have demonstrated that oral microorganisms can translocate into the gastrointestinal tract where they readily contribute to inflammation and even the generation of tumors. As such, the oral-gut axis, defined as a communication from the mouth to the intestines, has now become a critical focus in the management of oral and systemic disease. Research speculates that oral bacteria can migrate to the gastrointestinal tract and serve as a biomarker for both gastrointestinal and hepatic diseases.1

As dental professionals position themselves to better understand the complexities of their role in managing biofilm and its effects on oral disease, a provocative yet evidence-based concept has emerged: perhaps scaling procedures alone may leave a missing piece to the disease puzzle.

Oral microorganisms and the gut

While both the oral and gut floras have their own unique ecosystems, swallowing large gulps of oral bacteria as well as allowing these critters to enter the bloodstream via gingival bleeding permits the migration of oral bacteria to the gut. Long-standing research indicates a unique relationship between pathogenic microorganisms of the oral cavity and their role in gut health.

You may also be interested in ...

Retiring the "cleaning lady": A futuristic approach to treating oral disease

Gut health: How important is the food you eat?

Specifically, oral bacteria that has made its way to the gut has been linked to a variety of digestive diseases, including inflammatory bowel disease, colorectal cancer, pancreatic cancer, liver carcinoma, and liver cirrhosis.2 After colonizing in the digestive system, the oral bacteria will also be found in high concentrations in the feces of individuals with digestive disorders.

Put simply, the imbalance of healthy and disease-producing bacteria within the oral cavity eventually contributes to an imbalance in the gut microbiota, priming the digestive system for a myriad of digestive disorders. It’s worth considering that bacteria of oral origin cannot be completely removed from the body during a scaling visit.

The gut and the immune system

Current research notes that 70%–80% of the immune system thrives within the gut flora, making the digestive system a significant host of the immune system.3 In a healthy scenario, microorganisms within the gut provide communication and response signaling for immune cells. Additionally, the gut microbiota release metabolites, which are responsible for addressing inflammation. Gut flora in a healthy state plays a significant role in the management of disease and inflammation.

However, when there is a significant imbalance in the microorganisms of the gut flora, the host-body defense system becomes compromised.4 This is well observed, for example, in patients who receive a prescription for systemic antibiotics in which there are great concerns about the “wipe out” of all bacteria within the gut flora, thus priming the patient for opportunistic infections and gastrointestinal reactions.

This can also be observed in instances where oral bacteria have entered the gut flora, having created an imbalance or a dysbiotic state. The result: a compromised and dysfunctional immune system that can ultimately have an impact on wound healing during periodontal therapy.5

The role of probiotics in microbiota

Probiotics, defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host,”6 offer a solution for improving the diversity of both the oral and gut floras. One species that can be found in strain-specific probiotics, Lactobacillus reuteri, has demonstrated significant beneficial effects to both the oral cavity and the digestive system. L. reuteri is unique in that it is one of the indigenous bacterial strains of the human gastrointestinal tract and thus is able to adapt and colonize within the body.7

While the modern lifestyle of antibiotic usage, the Western diet, and an increase in personal hygiene have decreased the colonization of L. reuteri within human populations, probiotics containing ample concentrations of L. reuteri can provide a promising solution for stabilizing the gut and oral microbiota. As a result, patients who experience decreased levels of L. reuteri experience higher incidences of inflammatory diseases, while those placed on a probiotic supplement dense with L. reuteri experience a significant modulation of their host microbiota and can combat infection more readily.8

Probiotics in dentistry

While procedures such as scaling and root planing and coronal polishing have been long-established gold standards in the management of oral disease, probiotics have begun to demonstrate optimal clinical results, perhaps by efficiently colonizing hard-to-reach sites within the human body.

First, L. reuteri provides optimal antimicrobial activity and can inhibit the colonization of disease-producing microbes, thus remodeling the composition of host microbiota. L. reuteri has demonstrated a significant reduction in concentrations of Prevotella intermedia, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans, bacteria of oral origin that have been implicated in both oral and systemic diseases.9

Second, L. reuteri has demonstrated benefits to the host immune system. Specifically, it can support a healthy immune system by reducing inflammation. This is readily seen in the reduction of proinflammatory cytokines, the inflammatory regulators released by the body that can worsen the progression of disease particularly within the oral cavity.10

Finally, L. reuteri can support gut health by strengthening the intestinal barrier. L. reuteri may compete with pathogenic bacteria within the gut, decreasing the concentration of bacteria capable of translocating within the gut flora.8

The use of probiotics containing L. reuteri has provided significant and favorable results for patients experiencing oral inflammatory conditions.11 Additionally, routine use of probiotics containing L. reuteri can serve as a critical adjunctive therapy for addressing the delicate balances within the oral-gut axis, thus improving both oral and subsequent systemic health for dental patients experiencing high levels of oral disease.


The more research continues to unpack about the oral-gut axis, the more our role in bacterial modification comes into question. Dentistry’s contribution to the oral-systemic link has now extended well beyond simply scaling a patient to reduce bacteria within the oral cavity. We must now move to a comprehensive understanding of the delicate balance of oral microorganisms, their role in impacting immune function, and work to efficiently target pathogenic oral bacteria within the mouth and throughout the body.

Through the integration of strain-specific probiotics, particularly those high in L. reuteri concentrations, dental professionals can position their patients to improve immune function, optimize the colonization of healthy microorganisms throughout the oral and gut flora, and ultimately provide a gentle and natural approach to managing oral disease. 

Editor's note: This article appeared in the April 2023 print edition of RDH magazine. Dental hygienists in North America are eligible for a complimentary print subscription. Sign up here.


  1. Imai J, Kitamoto S, Kamada N. The pathogenic oral–gut–liver axis: new understandings and clinical implications. Expert Rev Clin Immunol. 2021;17(7):727-736. doi:1080/1744666X.2021.1935877
  2. Kitamoto S, Nagao-Kitamoto H, Hein R, Schmidt TM, Kamada N. The bacterial connection between the oral cavity and the gut diseases. J Dent Res. 2020;99(9):1021-1029. doi:10.1177/0022034520924633
  3. Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The interplay between the gut microbiome and the immune system in the context of infectious diseases throughout life and the role of nutrition in optimizing treatment strategies. Nutrients. 2021;13(3):886. doi:10.3390/nu13030886
  4. Yoo JY, Groer M, Dutra SVO, Sarkar A, McSkimming DI. Gut microbiota and immune system interactions. Microorganisms. 2020;8(10):1587. doi:10.3390/microorganisms8101587
  5. Shi N, Li N, Duan X, Niu H. Interaction between the gut microbiome and mucosal immune system. Mil Med Res. 2017;4:1-7. doi:10.1186/s40779-017-0122-9
  6. Morelli L, Capurso L. FAO/WHO guidelines on probiotics: 10 years later. J Clin Gastroenterol. 2012;46(Suppl):S1-S2. doi:10.1097/MCG.0b013e318269fdd5
  7. Sinkiewicz G. Lactobacillus reuteri in Health and Disease. Doctoral dissertation, Malmö University, Malmö. 2010. http://www.diva-portal.org/smash/get/diva2:1404283/FULLTEXT01.pdf
  8. Mu Q, Tavella VJ, Luo XM. Role of Lactobacillus reuteri in human health and diseases. Front Microbiol. 2018;9:757. doi:10.3389/fmicb.2018.00757
  9. Vivekananda MR, Vandana KL, Bhat KG. Effect of the probiotic Lactobacilli reuteri (Prodentis) in the management of periodontal disease: a preliminary randomized clinical trial. J Oral Microbiol. 2010;2(1):5344. doi:10.3402/jom.v2i0.5344
  10. Twetman S, Derawi B, Keller M, Ekstrand K, Yucel-Lindberg T, Stecksen-Blicks C. Short-term effect of chewing gums containing probiotic Lactobacillus reuteri on the levels of inflammatory mediators in gingival crevicular fluid. Acta Odontol Scand. 2009;67(1):19-24. doi:10.1080/00016350802516170
  11. Laleman I, Pauwels M, Quirynen M, Teughels W. A dual-strain Lactobacilli reuteri probiotic improves the treatment of residual pockets: a randomized controlled clinical trial. J Clin Periodontol. 2020;47(1):43-53. doi:10.1111/jcpe.13198
About the Author

Katrina M. Sanders, MEd, BSDH, RDH, RF

Katrina M. Sanders, MEd, BSDH, RDH, RF, is a clinical dental hygienist, author, and international speaker. She serves periodontal patients as the clinical liaison for Hygiene Excellence & Innovation for AZPerio and is the founder, CEO, and keynote speaker for Sanders Board Preparatory. Sanders is published in various publications including RDH magazine and Today’s RDH and is an advisory member for Modern Hygienist and the Dental Academy of Continuing Education. Recently, she proudly accepted the 2023 Denobi Award for Clinical Excellence and Innovation in dentistry.

Updated October 25, 2023