The Oral Microbiome: Where Gut Health Begins

By Dr. James Odell, OMD, ND, L.Ac.

The oral cavity has the second largest and most diverse microbiota after the gut, harboring more than 700 species of bacteria. It nurtures numerous microorganisms, including bacteria, fungi, viruses, and protozoa. The mouth, with its various niches, is an exceptionally complex habitat where microbes colonize the hard surfaces of the teeth and the soft tissues of the oral mucosa.

The teeth, tongue, cheeks, gingival sulcus, tonsils, hard palate, and soft palate provide a rich environment in which microorganisms can flourish. Interestingly, different surfaces within the mouth are preferentially colonized by specific oral bacteria because of adhesins on their surfaces, which bind to complementary receptors on oral tissues.

In addition to being the entry point for digestion, the oral microbiome is crucial for maintaining both oral and systemic health. It acts as a gatekeeper for overall health, with a balanced microbiome helping prevent oral diseases such as dental caries and periodontal disease while also influencing cardiovascular and immune health.

The commensal microbiota plays an important role in maintaining both oral and systemic health. An imbalance in the oral microbiota is responsible for the two most common oral diseases—dental caries and periodontal disease. Dental caries, or tooth decay, is the dissolution of tooth structure by acids produced during the fermentation of dietary carbohydrates by oral bacteria. In individuals who repeatedly consume high levels of carbohydrates, frequent acid production overwhelms the buffering capacity of saliva, resulting in repeated and sustained reductions in pH (increased acidity). In turn, this alters the composition of the oral microbiota, favoring aciduric species of bacteria.

Pathogens responsible for dental caries and periodontitis are believed to reside primarily in supragingival and subgingival plaque, respectively. Removal of dental plaque through brushing, flossing, and oral irrigation remains the fundamental measure for preventing oral disease. However, the oral microbiome also regulates the virulence of specific bacteria within dental plaque.

Additionally, oral bacteria in and around the gumline activate the immune system. In response, the immune system produces inflammatory molecules such as cytokines and chemokines to combat these bacteria. These signaling molecules can travel through the bloodstream and contribute to inflammation throughout the body. Chronic systemic inflammation has been associated with numerous health conditions, including cardiovascular disease and neurodegenerative diseases. Resident bacteria possess both pro-inflammatory and anti-inflammatory activities that are essential for maintaining homeostasis at heavily colonized sites such as the oral cavity.

The oral cavity is the initial part of the digestive tract and is followed by the esophagus, stomach, small intestine, and colon. The composition of the microbiome differs throughout each section of the digestive tract and depends on the unique environment of each organ. Consequently, there is an intimate connection between the oral microbiome and the gastrointestinal (GI) microbiome.

Commensal microorganisms in the gut are essential for maintaining the intestinal mucosa, supporting regeneration of the intestinal lining, and promoting the appropriate development of both local and systemic immunity.

Together, the oral and intestinal microbiomes contribute to numerous critical metabolic, physiological, and immunological functions, including:

• Differentiation and maturation of the host mucosa and its immune system

• Food digestion and nutrient absorption

• Energy generation

• Metabolic regulation and control of fat storage

• Processing and detoxification of environmental chemicals

• Maintenance of skin and mucosal barrier function

• Development and regulation of the immune system, including fine-tuning of immune responses—that is, maintaining the balance between pro-inflammatory and anti-inflammatory processes

• Prevention of the invasion and growth of disease-promoting microorganisms (colonization resistance)

he oral microbiota contributes significantly to oral and overall well-being, and disruption of this microbial community can have detrimental effects on human health. Fortunately, recent advances in genomic technologies, including next-generation sequencing and bioinformatics, have revealed the remarkable complexity of the oral microbiome. These advances have dramatically expanded our ability to study the oral microbiome and its influence on the body as a whole. As our understanding continues to grow, these diagnostic techniques may lead to promising new dental therapies and interventions designed to nurture and support a healthy oral microbiome.

References:

Bordenstein SR, Theis KR. Host biology in light of the microbiome: Ten principles of holobionts and hologenomes. PLoS Biology. 2015;13.

Devine DA, Marsh PD, Meade J. Modulation of host responses by oral commensal bacteria. Journal of Oral Microbiology. 2015;7:26941.

Gao L, Xu T, Huang G, Jiang S, Gu Y, Chen F. Oral microbiomes: More and more importance in oral cavity and whole body. Protein & Cell. 2018;9(5):488–500.

Kilian M, Chapple ILC, Hannig M, Marsh PD, Meuric V, Pedersen AML, Tonetti MS, Wade WG, Zaura E. The oral microbiome—an update for oral healthcare professionals. British Dental Journal. 2016;221(10):657–666.

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This article is for informational purposes only and is not intended to be a substitute for the direct care of a qualified health practitioner who oversees and provides unique and individualized care. The information provided here is to broaden our different perspectives and should not be construed as medical advice, diagnosis, or treatment.