Oral diseases starting with gingivitis double the risk of stroke already in working-age people, while intact molars can help keep the mind sharp.
In Finland, an oral disease more common than even tooth decay is periodontitis, which affects over 60 percent of the adult population. It is an inflammatory disease of the tooth-supporting tissue, with early symptoms including inflammation of the gum, and bleeding from the gum when brushing or flossing. Plaque and calculus accumulating on the surface of the teeth contribute to the development of periodontitis.
Advanced periodontitis can lead to the loosening and loss of teeth, but it can also significantly increase the risk of many other serious diseases by maintaining low-grade inflammation. “Inflammation can spread from the mouth to other parts of the body. Inflamed gums are also a gateway through which bacteria from the mouth can enter the bloodstream,” Professor of Translational Dentistry Pirkko Pussinen says.
The mouth harbours the second richest microbiome of the human body, i.e., a community of micro-organisms such as bacteria, yeasts and viruses – only the gut has more. In a healthy mouth, the microbiome is balanced, but in periodontitis, this balance is disturbed, and harmful bacteria take over. “These bacteria feed on the tissue destroyed by inflammation, and their proliferation, in turn, accelerates inflammation, creating a vicious cycle.”
The oral microbiome can still be restored to a healthy state by treating gingivitis, but not after it has advanced to periodontitis.
Pirkko Pussinen
Oral bacteria may contribute to the formation of blood clots
Recent years have seen studies exploring the association of periodontitis with stroke, for example. “People suffering from periodontitis have a 2 to 2.5 times higher risk of stroke while they’re still of working age,” says Pussinen, whose research group has just published new findings on the topic.
The study examined individuals under the age of 50 who had suffered a cryptogenic stroke – one that could not be explained by any of the traditional risk factors. It was found that periodontitis not only increased the risk of stroke, but its severity was also associated with that of stroke.
“The risk of stroke also increased after invasive dental treatments, such as root canal treatment and tooth extraction, especially in individuals with patent foramen ovale, PFO, a hole in the septum of the heart.”
Oral bacteria entering the bloodstream and PFO may both contribute to the formation of a blood clot leading to stroke. “However, we were able to obtain blood samples from patients only a few days after their stroke, at which point no biomarkers of bacteria could be found in their blood.”
PFO is common and usually does not require treatment. However, its association with stroke has been observed in other studies as well, and PFO closure procedures have been performed to prevent new strokes.
Molars stimulate the brain
Doctoral Researcher Sam Asher has examined the association of oral health with brain function from another perspective, namely that of cognitive decline and dementia.
Cognitive functions are related to information processing, such as perception, thinking and memory, and their deterioration can predict dementia.
“A review of previous research showed that periodontitis, and especially tooth loss, may be associated with the risk of dementia, so we decided to explore this in more detail. In Finland, there is a wealth of data available from the national Health 2000 and 2011 Surveys,” Asher says.
“It is generally thought that a person can manage with 20 teeth, so we are talking about genuine tooth loss when someone has fewer than 20 teeth.”
The Finnish data showed that tooth loss increased the risk of both cognitive impairment and dementia. “Rather surprisingly, the association was greatest when there were 10–19 teeth remaining. It may be that at this stage, the other detriments of tooth loss are compounded by a greater burden of inflammation than in a situation where there are no longer teeth left that could maintain inflammation”, Asher notes.
Another study by the group showed that it is of particular consequence which teeth are missing. “The loss of anterior teeth did not matter, but the loss of molars increased the risk of dementia, and the risk was greater the more pairs of opposing molars were missing from the upper and lower jaw.”
According to Asher, there can be many reasons for this, one being that as opposing molars are in constant contact with each other, continuous stimulation is transmitted to the brain via the nerves in the roots of teeth. “In animal studies, the loss of this molar stimulation has been linked to atrophic changes in the hypothalamus and declining cognitive functions.”
Tooth loss can affect brain health also through deteriorated nutrition and quality of life. In these studies, dentures were found to have some protective effects, but they did not compensate for the loss of molar pairs.
The loss of molars increased the risk of dementia, and the risk was greater the more pairs of opposing molars were missing from the upper and lower jaw.
Sam Asher
Oral health is associated with blood lipids
The importance of the gut microbiome for health is widely discussed, and oral health also plays a role in it, as the bacteria we swallow in our saliva can end up in our gut, too. “Indeed, unfavourable changes in the gut microbiome have been observed in patients with periodontitis,” Pussinen notes.
For instance, pathogenic bacteria from the mouth can promote inflammation and permeability of the intestinal wall, thereby allowing microbial elements to enter other parts of the body. “This can, for its part, maintain low-grade inflammation in the body.”
A recent comprehensive study led by Pussinen found periodontitis and caries to be associated with changes in the concentration of several metabolic markers that are indicative of an increased risk of cardiovascular disease. Many of these changes pertained to lipid and cholesterol metabolism, suggesting that oral infections could, to a degree, explain abnormal blood lipids.
Periodontitis can also raise blood pressure and impair the management of diabetes. “Oral infections complicate blood glucose control and can increase the risk of comorbidities, so it is especially important for diabetics to take care of and seek treatment for oral health. High blood glucose, on the other hand, fuels oral infections. This affects a large part of the population in Finland as well.”
The association of oral diseases with common chronic diseases and, for example, autoimmune diseases may be partly explained by the fact that these diseases may share a common genetic background. “In Finland, the FinnGen project has provided a fantastic opportunity to investigate this, and we will be much wiser about this topic soon.”
In the future, each individual’s genetic predisposition to oral diseases could be considered in, for example, the selection of targeted treatments and in more frequent monitoring.
Exploring the genetic background of various diseases, the national FinnGen project has collected the genomic data of a total of 500,000 Finns so far. Pussinen chairs the project’s group of experts in clinical dentistry.
The oral virome remains a mystery
“The oral microbiome can still be restored to a healthy state by treating gingivitis. However, once gingivitis has advanced to periodontitis, the microbiome cannot be restored to its original state even if the inflammation is treated,” Pussinen says.
A balanced oral microbiome can be supported by the same healthy foods that support gut microbes: by eating fibre-rich foods and avoiding sugar and saturated fats. There are also products available on the market that are designed to balance the oral microbiome, but Pussinen points out that not even researchers fully understand all components of a balanced or an imbalanced oral microbiome yet.
“At the moment, plenty of research is being done into the intense communication between bacteria, which they conduct through vesicles they secrete. The significance of the oral virome, or the numerous viruses present in the mouth, has begun to be explored only recently.”
Many of the viruses that live in the mouth are bacteriophages, meaning they can infect bacteria, exchange genetic material with them, and alter the bacterial characteristics in the mouth. Indeed, it has been envisioned that viruses could be harnessed to treat oral diseases.
Good oral hygiene from childhood could minimise risks
Conducted in Kuopio, the Physical Activity and Nutrition in Children study recently found associations between oral bacteria and risk factors for metabolic syndrome already in elementary school-aged children. According to Pussinen, parents should be aware of the fact that good oral hygiene learned in childhood could reduce many health risks.
“Admittedly, dental care is a skill that many adults struggle with, too, and some sort of informational campaigns on the subject would be needed.”
Finland’s first dental Good Practice Consensus Guideline on the intervals for oral examinations and treatments in healthcare was published recently. It advises that healthy adults without oral diseases or their risk factors should undergo an oral examination every two to four years. For those with oral diseases or risk factors, examinations should be conducted every one to two years, depending on the individual’s situation. Adults are generally not sent invitations to oral examinations; instead, they must schedule appointments on their own initiative.
“In many other countries, it is recommended to have a dental check-up every six months. Our next step will be to examine national data to see how the use of oral health care services may potentially affect other health risks,” Asher says.
Instructional videos on how to clean teeth, and guides for taking care of oral health for different age groups can be found, for example, on the Clean Teeth website available at: https://www.helsinki.fi/en/projects/clean-teeth
