When it comes to studying the human microbiome in relation to systematic health, gut bacteria had always been the focus. However, more research is showing the strong influence that the oral care microbiome also has over the health and wellness of the human body.
The oral microbiome describes the 700+ microorganisms found on the tongue, teeth, gingiva, palates, and tonsils. The diverse community of fungi, archaea, protozoa and bacteria are imperative for health and directly connects with the sinuses, larynx, trachea and lungs.
Poor oral microbiome condition is not only associated with oral diseases like tooth decay, it’s also been linked to the development of serious conditions like rheumatoid arthritis and inflammatory bowel disease, to name just two.
Although there has been plenty of innovation in toothpastes and mouthwashes that support a healthier oral microbiome, there are still many opportunities to improve this category in terms of the potential health and disease prevention benefits for the entire body – not just in relation to mouth diseases and bad breath.
According to CEO of microbiome certification company MyMicrobiome Dr Kristin Neumann, recent studies also hint at a connection between the oral microbiome and plaque with cardiovascular diseases and Alzheimer's disease.
“The oral microbiome is dominated by a bacterial species called Streptococcus,” explained Dr Neumann. “Bacteria colonise in the oral mucosa, on the teeth, and on the tongue. The mouth is the entrance to the most densely populated microbiome in the human body, the gastrointestinal tract.”
In terms of current trends, she said she is currently seeing more probiotic oral care products like toothpaste, mouthwashes and chewing gum being tested. Mouthwashes in particular are being formulated in a milder, less antibacterial way. “We just certified the first microbiome-friendly ingredient for the mouth which is based on Aloe Vera,” she shared.
Oral microbiome: the first line of defence?
Bacteria in the mouth are thought to play an important role in general immunity. A recent observational study that was published in eBioMedicine in July 2023 found that severe cases of Covid-19 resulted in a significant reduction in oral microbiome diversity, yet milder cases didn't impact the oral microbiome.
The research was led by Abigail Armstrong at the Rutgers Center for Advanced Biotechnology and Medicine who concluded: "This means that major events like serious illness and treatments are needed to change this resilient microbiome."
While it's good news that this microbiome is resilient, imbalances in it can play a part in causing both physical and mental diseases.
A recent study published in Biological Psychiatry journal studied the link between the human microbiome and mental health and found that the oral microbiome is especially susceptible to the intake of highly fermentable carbohydrates. Similarly to the gut microbiome, it has also been implicated in mood disorders and other brain conditions.
Two small studies have reported associations between levels of taxa in the saliva of young people with depression and anxiety symptoms with potential mediation via basal C-reactive protein and cortisol levels.
Differences in oral bacterial taxa have also been observed in subgingival samples of those with bipolar disorder compared to healthy controls.
It appears that oral microbiome potentially influences mental health conditions by direct translocation of microorganisms from the oral cavity to the brain through facial nerves and the olfactory bulb , along with the disruption of the oral-gut microbiome axis, which can cause neuroinflammation.
Starting young: the oral microbiome for infants
It seems that the influence of the oral microbiome on our systematic health starts from even before we are born.
A recent review published in Frontiers in Microbiology explores how the oral microbiome develops in infants, focusing on early nutrition and environment to help scientists use this research to develop more effective health guidelines.
Bacteria, such as Staphylococcus epidermidis, begin to colonise oral cavities before birth. However, the oral microbiome is dynamic at this point and experiences a lot of changes in early life. By the time a baby is one month old, S. epidermidis has almost disappeared and other genera like Gemella and Haemophilus emerge.
The oral microbiome composition continues to be unstable as the baby's teeth develop and is introduced to new foods, then it starts to stabilise around the age of four.
Microbes in breast milk can also influence oral microbiome development and breast milk-fed babies have distinctly different microbiomes from those given formula, which is noticeable within days of birth.
Breastfed babies have more Streptococcus, Neisseria, and Actinobacillus, while formula-fed babies have more Haemophilus, Veillonella, and Weeksellaceae. The microbiomes of formula-fed babies were also more species-rich.
Researchers are still unsure about how breast milk shapes the oral microbiome. However, they do know that lactoferrin, lysozyme, and secretory immunoglobulin A (sIgA) – antimicrobial proteins found in breast milk – can protect children from various diseases.
Other than microbes, breast milk also contains human milk oligosaccharides (HMOs), which are prebiotics that allow bacteria like Bifidobacterium to grow, which may also prevent tooth decay by protecting against S. epidermidis.