What is dental plaque?

Dental plaque is a collection of many types of bacteria and other microorganisms embedded within a biofilm on the surface of teeth. This biofilm is a sticky film secreted by microorganisms that allows them to adhere to teeth and protects them from being washed away by saliva or ingested food and drinks. As this biofilm accumulates and spreads along the tooth surface below the gumline, it increasingly favours the growth of bad bacteria which are implicated in the development of poor dental health, such as dental cavities, gum inflammation (gingivitis and periodontitis), and bad breath. Dental plaque needs to be controlled by regular tooth brushing and flossing, which is able to disrupt the biofilm and keep the number of bad bacteria living on teeth under control. This helps to prevent the development of poor dental health. If teeth aren’t cleaned properly, the biofilm accumulates minerals such as calcium and becomes hardened over time – this is what we call ‘tartar’, and is seen as a brown or yellow discoloration on teeth. Tartar cannot be removed by tooth brushing or flossing, and must be removed by professional dental cleaning (3, 4, 5).

Why is it important to have a healthy oral microbiome?

When the oral microbiome is healthy and your dental plaque is kept under control, your overall dental health benefits and you are less likely to experience common dental diseases such as:

- Dental cavities
- Gum inflammation
- Bad breath
- Oral thrush
- Mouth ulcers

The clean surfaces of teeth are initially populated by specific groups of beneficial bacteria, such as many different species of Streptococcus and Actinomyces. The presence of these bacteria are important in maintaining oral health for a number of reasons (6, 7).

The oral microbiome and gum health

A healthy oral microbiome promotes good gum health and prevents gum inflammation by preventing the buildup of bad bacteria which can cause inflammation. For example, these bacteria help to prevent bad bacteria and yeasts from becoming part of the oral microbiome. They do this by competing for space and nutrients so that it is harder for unwanted microorganisms to survive. Beneficial bacteria will also secrete specific antimicrobial compounds that assist with this process, creating an inhospitable environment directly around them. Some disease-associated microorganisms are a natural part of the oral microbiome, but the presence of beneficial bacteria helps to prevent them from replicating, disrupting healthy microbial balance and causing disease (3, 7).

The oral microbiome and dental plaque accumulation

If the biofilm created by beneficial bacteria is not kept under control by regular tooth brushing, flossing and dental cleaning, it creates an environment that allows for bad bacteria to get a foothold. The increasing thickness of the biofilm and the spreading of plaque down below the gumline changes the environment, reducing oxygen levels and replacing carbohydrates with protein as the main nutrient available for energy production. Low oxygen and low carbohydrate availability makes it harder for many beneficial bacteria to survive, while the same conditions allow harmful microorganisms to thrive. Within this environment, bad bacteria will crowd out the beneficial bacteria (4, 6).


The oral microbiome and gum inflammation

When the concentration of bad bacteria within the oral microbiome and dental plaque increases, the mouth’s immune system recognises this as an infection and begins a highly-inflammatory attack to reduce the build up of these bacteria (7).

Unfortunately, gum tissue becomes inflamed and damaged in the process. This is known as ‘gingivitis’, and is one of the most common diseases of the gums. The most common symptoms of gingivitis include red, swollen and bleeding gums, and it can also contribute to bad breath. Sensitivity to heat and cold, tenderness upon touch, and a dark red shiny appearance are also symptoms of gum inflammation. If left untreated, gingivitis progresses to a more severe form of disease called periodontitis. In periodontitis, untreated gum inflammation leads to the breakdown of the supporting tissues of teeth, including the gums - this is one of the major causes of receding gums or ‘gum recession’ (7, 8).

When damage to gum tissues starts to occur, the by-products of tissue breakdown also feed harmful bacteria. This creates a vicious cycle: bacteria that cause inflammation and tissue damage feed off the by-products of tissue breakdown and are able to proliferate further, causing more inflammation and tissue damage. This cycle, which is a hallmark of periodontitis, results in severe gum recession, irreversible damage to the tissues that support teeth, and eventual loss of teeth (3).


Preventing gum disease

Therefore, we need to work with our beneficial bacteria to keep dental plaque build up low so that the conditions remain optimal for their survival. By keeping harmful microorganisms at bay, a healthy oral microbiome can promote good gum health and prevent gum inflammation and other diseases of the gums. Alongside regular tooth brushing and flossing, specific probiotics can be used to support the oral microbiome and provide protection against dental plaque accumulation and poor gum health.

How do probiotics protect against dental plaque and reduce gum inflammation?

Specific oral probiotics can target the problematic bacteria within the oral microbiome that contribute to dental plaque accumulation, reducing their ability to grow within the mouth. They can do this by producing specific antimicrobial compounds, and taking up space to crowd out these bad bacteria. By reducing dental plaque accumulation and the concentration of harmful bacteria within the oral microbiome, these probiotic strains can also help to reduce gum inflammation. Specific probiotic strains have also been found to modulate the immune system. This can help to reduce the amount of inflammation that is created in response to dental plaque build up, and reduce inflammatory damage to gum tissues. This action also reduces the presence of tissue breakdown by-products, which would be used by bad bacteria to proliferate further.

Clinical trials have shown that people who use a combination of four probiotic strains (Lactobacillus helveticus Rosell®-52, Bifidobacterium longum Rosell®-175, Lactobacillus rhamnosus Rosell®-11 and Saccharomyces boulardii CNCM I-1079) alongside regular tooth brushing have up to 71% less dental plaque accumulation and up to 73% less gum inflammation compared to those who took placebo after just 14 days. In many of these trials, this combination of probiotic strains was compared to chlorhexidine, an antimicrobial mouthwash commonly prescribed by dentists, and was found to be just as effective (9, 10).

The oral microbiome for healthy teeth and cavity prevention

A healthy oral microbiome is also necessary for healthy teeth, specifically for the prevention of cavity formation. Certain bacteria within dental plaque use sugar from our diets to create energy and produce acids as a waste product. These acids have the potential to break down tooth enamel and lead to cavity formation. However, beneficial bacteria which produce alkaline metabolites (higher pH) counteract these acids (lower pH), creating a neutral environment that protects tooth enamel, reverses any damage that has occurred and prevents tooth decay. The number of bacteria which use sugar to produce acid are kept under control when we avoid frequent snacking on sugary foods, regularly clean our teeth, and support the population of beneficial bacteria which can neutralise acids (3, 7).

Oral microbiome imbalance, cavity formation, and tooth decay

However, frequent exposure to sugar and poor dental hygiene can allow these cavity-forming bacteria to outgrow beneficial bacteria. As the diminished population of beneficial bacteria is unable to effectively neutralise the increasing concentration of acids in the biofilm, they create a highly acidic environment that erodes tooth enamel (essentially dissolving the minerals that make up this protective coating). As acids erode tooth enamel, cavities form and tooth decay follows (7, 11).

Can probiotics help with dental cavities?

Specific probiotic strains can help to reduce the concentration of bacteria which are associated with the development of dental cavities. One of the main bacteria which is linked to dental cavities is Streptococcus mutans. A combination of four probiotic strains, Lactobacillus helveticus Rosell®-52, Bifidobacterium longum Rosell®-175, Lactobacillus rhamnosus Rosell®-11 and Saccharomyces boulardii CNCM I-1079, has been shown to reduce the concentration of Streptococcus mutans in saliva. In one clinical trial, participants who used this combination of probiotic strains once a day for 14 days alongside regular tooth brushing had 87.6% less Streptococcus mutans in their saliva than those who took placebo. By reducing the concentration of bacteria like Streptococcus mutans, specific oral probiotics may help to reduce the risk of dental cavities when used alongside good oral hygiene practices (12).

The oral microbiome and bad breath

Halitosis, commonly known as ‘bad breath’, is caused by a buildup of bacteria which can produce malodorous (smelly) gases. After we eat, food particles that remain in the mouth are used by bacteria as a fuel source. Bacteria which break down protein produce volatile sulphur compounds or ‘VSCs’, a group of malodorous gases –which are the main cause of bad breath– as a waste product. The bacteria that create these gases accumulate on the surface of the tongue and in dental plaque in between teeth. A high concentration of these microorganisms within the oral microbiome increases the production of VSCs, resulting in bad breath (13, 14).

The link between bad breath and gum inflammation

Bacteria which have been linked to halitosis are also linked to gingivitis and periodontitis, such as Porphymonas gingivalis, Treponema denticola, Fusobacterium nucleatum and Prevotella intermedia. When these bacteria overgrow and create gum inflammation, the breakdown of gum tissue caused by this inflammation releases additional proteins that can be used to produce VSCs. This is why halitosis is often observed in patients with gingivitis and periodontitis (14).

Can probiotics improve bad breath?

Specific probiotic strains may help to reduce the severity of halitosis by reducing the concentration of bad bacteria available to produce malodorous gases. For example, in-vitro clinical studies have demonstrated the combination of three specific probiotic strains, Lactobacillus helveticus Rosell®-52, Bifidobacterium longum Rosell®-175 and Lactobacillus rhamnosus Rosell®-11, can reduce the growth of a wide range of halitosis-related bacteria.They have also been shown to reduce the amount of VSCs produced by these bacteria in-vitro. Specific probiotic strains which have been shown to reduce dental plaque accumulation, as dental plaque can harbour halitosis-related bacteria, and reduce gum inflammation, which provides additional proteins for bacterial VSC production, can also help to reduce halitosis.

Can the oral microbiome impact other areas of my health?

Research is showing that oral health has a significant impact on our overall health and wellbeing, and poor oral health has been associated with a number of chronic diseases. The oral microbiome, as one of the main influencers of our oral health, plays a large part in this process (2).

Blood vessels supplying gum tissue are in close contact with dental plaque that sits below the gum line. We can see this by how easily our gums can bleed. When dental plaque causes gum inflammation, this allows the mediators of this inflammation to enter the bloodstream and cause inflammation in other parts of the body. When our dental health is poor and harmful bacteria and their endotoxins accumulate within the mouth, they are inevitably swallowed. This has the potential to cause problems with our digestive system, or enter the bloodstream via another absorption in the digestive tract and impact other organ systems (2).

These channels allow inflammatory mediators, toxins and bacteria themselves to travel between the oral cavity and systemic circulation, creating a relationship between poor dental health and other systemic diseases. Associations between poor dental health and many systemic diseases are now beginning to emerge in the research, including cardiovascular disease, obesity, diabetes, pregnancy complications, Alzheimer’s disease, autoimmune diseases such as rheumatoid arthritis, osteoporosis and many others (2).

How do probiotics support a healthy oral microbiome?

In summary, specific probiotic strains can support a healthy oral microbiome by two main mechanisms:

Directly reducing the growth of bad bacteria and yeasts and reducing dental plaque accumulation.
Creating an oral environment that supports the growth of a healthy oral microbiome.

Probiotics can help to target a number of bad bacteria and yeasts linked to poor dental health, including:

- Candida species related to oral thrush
- Streptococcus mutans related to cavities
- Halitosis-associated bacteria
- Bacteria associated with dental plaque accumulation and poor gum health

These effects are attributed to the production of targeted antimicrobial compounds by probiotic strains in the mouth, and their ability to outcompete these bad bacteria and yeasts in the oral environment. As a result of their action on harmful bacteria and yeasts, probiotics can help to reduce dental plaque accumulation and reduce the risk of cavities, bad breath and oral thrush in combination with regular dental hygiene.

Probiotics that reduce dental plaque accumulation can also help to reduce gum inflammation and improve gum health. Some probiotics can also help to reduce gum inflammation by improving the function of the immune system. By reducing the level of inflammation created in response to bacteria within dental plaque, these probiotics can help to improve gum health. Some probiotics can also increase the pH of saliva, and this may help to prevent the growth of harmful bacteria and yeasts that thrive in an acidic environment such as the cavity-forming bacteria Streptococcus mutans and counteract their pH-lowering effects. By reducing gum inflammation and increasing salivary pH, probiotics can help to create an oral environment that favours the growth of beneficial oral microorganisms over more harmful species.

Do all probiotics provide benefits to the oral microbiome and dental health?

Not all probiotics will provide benefits to the oral microbiome and dental health, and there are a number of factors which can influence if a probiotic will be beneficial for your oral health.

Firstly, different probiotic strains (even within the same species) can have very different genetics and behave very differently within the human body. Probiotics become alive with activity when they enter the human body. They interact with all kinds of cells and, just like the microorganisms within our own microbiome, they turn our food into energy and produce bioactive compounds called metabolites in the process. Different probiotic strains produce different metabolites, and interact with cells in different ways. As a result, different probiotic strains will offer vastly different health benefits. Scientific research helps us to identify what health benefits a specific probiotic strain can offer (15).

Therefore, if you are looking to use a probiotic to support your oral health, you must use probiotic strains which have been put through clinical research and shown to benefit the oral microbiome or improve dental health in some way.

These probiotic strains also need to be delivered in a format that allows them to interact with the oral microbiome and cover the oral cavity, including the teeth, tongue and gums. Probiotics in capsules will not be able to perform this function.Delivery methods which provide the best contact between probiotic microorganisms, the oral microbiome and the surfaces of the mouth include:

- Probiotic powders which can be mixed with water and used as a mouthwash
- Probiotic powders which are designed to ‘melt’ in the mouth as they are swished around
- Chewable tablets

How do I incorporate probiotics into my oral hygiene routine?

Probiotics for oral health are designed to be used alongside regular tooth brushing and flossing. Using them after your nightly oral hygiene routine and immediately before bed allows them to coat the mouth and interact with the oral microbiome while you sleep, without being washed away by food or drink.

They can be used instead of antimicrobial mouthwashes to provide additional benefits to dental health, with research demonstrating that using specific probiotic strains alongside regular dental hygiene can provide additional protection against dental plaque accumulation, improve gum health, reduce bad breath, and reduce the risk of dental cavities.

The advantage to using a well-researched oral probiotic over antimicrobial mouthwashes is the sparing effect that probiotics have on good bacteria, which antimicrobial mouthwashes do not. That means that you are protecting the beneficial bacteria in your mouth, which are essential for your ongoing oral and whole body health. When probiotics can help to reduce dental plaque and gum inflammation by selectively reducing bad bacteria, the good bacteria left behind are able to flourish. This can help to either prevent or prolong the return of bad bacteria that contribute to plaque build-up, poor gum health, cavities and bad breath (16).