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Dental Diseases are More than Just 'Issues Within the Mouth'

—The Connection Between 'Oral Health' and 'Cognition'"

by Takayoshi Hashimura,

Director of Soccer Street Minami Dental Office

The strategy against dementia requires regular prevention. In this article, dentist Takayoshi Hashimura, the Director of Soccer Street Minami Dental Office, explains the deep connection between 'oral health' and the risk of dementia.

Table of Contents:

   1. Anyone Can Develop Dementia

   2. The Risk of Developing Dementia Increases 'As Teeth Are Lost'

   3. How Does the Inability to Chew Lead to Dementia?

   4. Can 'Oral Bacteria' Exacerbate Alzheimer's Disease?

   5. The First Step to Preventing Dementia is 'Oral Health'

1. Anyone Can Develop Dementia

Japan, the world's most aged country, with an aging rate of 29.1% in 2022, is experiencing an increase in the number of dementia patients. In 2012, 15% of people aged 65 and over, or about 4.62 million people, had dementia (including Mild Cognitive Impairment). By 2025, it is predicted that this will reach 20%, with 7.31 million people suffering from dementia.

While no one wants to develop dementia, given the reality that so many people are developing it, one cannot simply say, "I'm absolutely fine, I won't get dementia." Instead, it's necessary to prepare oneself with the mindset that "I might develop it too."

Prevention is key to combat dementia, and in this regard, I will discuss how maintaining 'oral health' is crucial for dementia prevention.

2. The Risk of Developing Dementia Increases 'As Teeth Are Lost'

Dementia is closely related to the loss of teeth. The more teeth are lost, the higher the risk of developing dementia. Humans have 28 teeth, excluding wisdom teeth, but with age, teeth are lost due to dental diseases and other causes.

Research has shown that when the number of teeth decreases to 19 or fewer, the risk of developing dementia increases by 1.2 times. A national health survey in the United States in 2022 reported that people with 'edentulism', or no teeth at all, had the highest cognitive impairment. Similarly, other research showed that their risk is increased by 1.85 times.

While it is crucial not to lose teeth, what percentage of each generation has fewer than 20 teeth, the threshold that increases the risk of dementia? According to the 2016 Dental Disease Status Survey by the Ministry of Health, Labour and Welfare, only 1% of people between 45 and 49 years of age have fewer than 20 teeth. However, the percentage increases with age, with 14.8% for those aged 60-64, 36.6% for those aged 70-74, and 55.8% for those aged 80-84.

Regarding the causes of tooth loss, periodontal disease is the most common (36.6%), followed by tooth decay (29.2%). More people lose teeth due to periodontal disease than cavities. The age of the subjects in this survey is 58. Since periodontal disease increases with age, tooth extraction due to periodontal disease also increases with age.

From my actual clinical experience, tooth extractions in the 20-30 age group are mostly due to cavities. Still, from the 40s onward, extractions due to periodontal disease increase, and by the 60s, I find that about 80% of tooth extractions are due to periodontal disease.

The Ministry of Health, Labor, and Welfare, together with the Dental Association, is promoting the '8020 Movement'. The 8020 Movement aims to maintain 20 or more teeth by the age of 80 to maintain the Quality of Life (QOL), which includes the expected effect of preventing dementia.

As of the 2016 Dental Disease Status Survey, the achievement rate was 51.2%, which increased from the results of the 2011 survey. However, considering that we have entered the era of living to 100 years, this initiative becomes even more crucial from here on.

3. How Does the Inability to Chew Lead to Dementia?

How does the loss of teeth, or the subsequent reduction in chewing ability, change our lives, and why does it increase the risk of dementia?

• Dietary bias

It's easy to imagine that as teeth are lost, some foods become more difficult to chew, or can't be chewed at all. For example, vegetables like cabbage fall into the category of foods that are hard to chew. Some types of meat also fall into this category.

If one's diet becomes biased, the nutrients obtained from food tend to become deficient, leading to a state known as 'frailty'. Frailty denotes a 'weak' physical state, and the term 'oral frailty' is collectively applied to symptoms and conditions caused by decline within the mouth.

Dementia is not a disease that occurs 'suddenly'. It starts from frailty and gradually progresses. Avoiding frailty can contribute to the prevention of dementia.

• Not chewing well leads to cognitive decline

The common saying that 'not chewing well leads to cognitive decline' is indeed true. When chewing ability decreases, stimulation to the cognitive region of the brain decreases, which can lead to memory disorders. The amount of blood flowing to the brain also decreases, reducing the nutrients necessary for the brain's activity, making it more susceptible to dementia.

• Difficulty in Saliva Production

Various factors can reduce saliva secretion, including diabetes, medication, mouth breathing, and sustained tension. Moreover, when you lose teeth and can't chew, the salivary glands (where saliva is produced) atrophy, and the amount of saliva also decreases. This is what's commonly known as dry mouth.

Dry mouth is a very troublesome condition. When you have dry mouth, periodontal disease can rapidly worsen, or you may develop many cavities. When tooth loss is accelerated by dry mouth, it also becomes one cause of dementia.

4, Can 'Oral Bacteria' Worsens Alzheimer's Disease?

Periodontal bacteria are resident bacteria in our mouths. There are several types of periodontal bacteria that coexist with other bacteria, creating a nest called the microbiome and proliferating. When they proliferate, periodontal disease worsens. Among these periodontal bacteria, a representative harmful type, 'P.g bacteria', has been identified, and it is becoming apparent from multiple studies that this P.g bacteria may exacerbate Alzheimer's disease.

Alzheimer's disease is a disease that causes brain atrophy. The most significant characteristic of this disease is the accumulation of a protein called amyloid-β plaque in the brain. A 2015 study first discovered in humans that P.g bacteria are involved in the accumulation of amyloid-β plaques. A 2019 study found that P.g bacteria cause macrophages (a type of white blood cell that protects the body from viruses and others) to accumulate amyloid-β plaques and migrate into the brain.

Alzheimer's dementia is the most common type of dementia. From this, it can be said that severe periodontal bacteria are directly involved in dementia.

5, The first step in dementia prevention is 'oral health'

Oral health is extremely important for dementia prevention. There are three key points to maintain oral health.

Point 1: Avoid oral frailty

As briefly mentioned earlier, oral frailty is a relatively new term proposed about a decade ago. According to the Japanese Dental Association, it starts with minor declines in oral function such as reduced pronunciation, food spillage, slight choking, and an increase in foods that can't be chewed.

Such symptoms start with tooth loss and muscle weakness. As mentioned before, periodontal disease is greatly involved in tooth loss. Daily self-care of your mouth to prevent periodontal disease is essential. The Japanese Dental Association also recommends oral exercises to prevent muscle weakness. If you notice the above symptoms, it is recommended to consult a dental clinic.

Point 2: Always keep your saliva power at full strength

Although saliva is more than 99% water, it plays a very important role. The water itself promotes the self-cleaning action of the mouth and suppresses the proliferation of cariogenic and periodontal bacteria. Saliva also contains digestive enzymes that aid digestion. It even has anti-cancer properties. Furthermore, it secretes a hormone called parotin, which boosts metabolism and has anti-aging effects.

Saliva, which has many benefits, decreases with aging for various reasons, and many people experience this. We, dental healthcare providers, also frequently encounter patients with dry mouth, which is a troublesome disease as mentioned earlier.

Not only does dry mouth make it difficult to wear dentures due to painful rubbing because the mouth is dry, or to eat and swallow dry food, but it also makes it easier to get cavities. Some people even wake up at night due to a dry mouth. Furthermore, bacteria that were originally suppressed by saliva proliferate, causing bad breath and candidiasis.

Here are five rules (a-e) to maintain your saliva power.

       a. Perform salivary gland massage

There are three large salivary glands in your mouth. Massaging these glands makes it easier to produce saliva due to the stimulation.

<Simple! Salivary gland massage anyone can do>

The three salivary glands are located around ① the upper molars (= parotid gland), ② the inside of the lower jaw tip (= sublingual gland), and ③ the inside of the lower jaw where the gills protrude (= submandibular gland).

The exact points can vary a bit between people, but try massaging as shown in the figures below. The spot where saliva slowly starts to come out is the location of the salivary gland.

       b. Relax

Saliva secretion is controlled by the autonomic nervous system. When you are tense, it is harder to produce saliva. It's especially important to relax at night.

       c. Talk, sing karaoke

A great way to moderately move your mouth is to "talk". Eating also moves your mouth, but it is short in time and not sufficient.

Stimulation to the mouth through conversation promotes saliva secretion. Singing karaoke is also a good option. It kills two birds with one stone by providing communication as well.

       d. Check your medications

As people age, the number of people who need to take medication increases. Some medications can cause dry mouth.

For example, antihistamines often used for hay fever. Antihistamines can cause dry mouth as a side effect. If you feel a dry mouth from taking medicine and it causes problems, consult with your healthcare provider.

       e. Use a mouth spray

While they do not have a sustained effect, mouth sprays can be effective. In addition to sprays, there are also gel-type and mouthwash-type products. It's a good idea to use them before and after meals or before going to bed.

Point 3. Establish a regular doctor

It's been reported that people who don't have a regular dental office have a 1.44 times higher risk of developing dementia than those who do. The advantage of having a regular doctor is that they can understand how the patient arrived at their current oral condition. It allows for more precise treatments and oral instructions that follow the patient's history. Also, the relationship of trust between the patient and the dentist is important. Maintaining oral health through self-care and professional care can help prevent dementia.

In conclusion, I've discussed the relationship between oral health and dementia prevention. Oral hygiene is a barometer of health. Let's work on dementia prevention through daily life and regular dental visits.

*This manuscript is a reprint from 'Saison's Big Study on Living' published in Japanese on April 10, 2023." You can access the original article from the following link:


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