Big Talk

Oral Care is Essential for a Long, Healthy Life

Ryutaro Kobayashi is a professor of dental surgery at Nippon Dental University, the world’s largest dental university. Established 114 years ago, it was the first dental school in Japan. Kobayashi is working to promote oral care based on the fact that mouth health affects other parts of the body. Toshio Motoya spoke with Kobayashi about trends on the front lines of dentistry, which is transforming from a field focused on drilling teeth to one that helps patients live healthy lives.

Falling asleep after drinking alcohol leads to tooth erosion

(M) Thank you for joining me on Big Talk today. Your specialty is dental surgery, which I assume is an unfamiliar term to many.

(K) Thank you for inviting me. First, I’d like to tell you about my field of dental surgery. This refers to external care, including surgical treatments. Specifically, we treat malignant and other diseases that occur in the mouth, including technically challenging tooth extractions and diseases of the mucous membranes and bones. This is the field that accounts for the largest number of referrals to the Nippon Dental University (NDU) Hospital. In the past many people have assumed dentistry is nothing more than drilling teeth, but it is actually a type of medical care that deals with overall oral health, including functions like eating, drinking, and talking. I think being able to enjoy eating is very important.

(M) When I asked why all of my American friends have beautiful teeth, they said they had braces when they were young. South Koreans also improve their teeth with orthodontics. It seems that Japanese people pay little attention to teeth and the mouth.

(K) Japanese people used to see teeth as unimportant, but things are changing in a positive direction. I feel like people disregarded the importance of teeth when you and I were young. All children age three and 12 had tooth decay (cavities). However, children of those ages today only have tooth decay on less than one tooth, on average. Tooth decay in children has rapidly decreased over the past 30 years. The concept is becoming steadily rooted in Japan that we must have good oral hygiene – founded on the importance of teeth and mouth functions – even before a baby’s first tooth appears.

(M) I feel like parents have the responsibility to care for their children’s teeth…

(K) Yes, I think this depends on the home environment where they are raised and the customs in their family.

(M) I remember people used to only brush their teeth in the morning. What is the proper number of times to brush daily?

(K) Experts have different opinions on this, but I brush after each meal for the sake of good manners.

(M) I can brush my teeth at home in the morning and at night, but it’s hard for me at lunch since I eat out a lot.

(K) The ideal is to be in an environment where you can brush after each meal. However, you produce saliva while talking, eating, and drinking during lunch. Saliva helps keep the mouth clean. In contrast, less saliva is produced during sleep. The mouth retains heat at a temperature of 36°C during slumber, so it is full of bacteria when you wake up in the morning. I immediately brush my teeth with a toothpaste made from natural ingredients after waking up. It doesn’t have any lingering fragrance, so it’s good for brushing even right before a meal. Even if you can’t brush during the day, one way to have good hygiene is to gargle frequently and make sure to do a good job brushing at night and in the morning.

(M) Does gargling help prevent cavities?

(K) It has some ancillary effects, but the best thing is to mechanically remove debris by scrubbing. Think about washing dishes – you can get more dirt off by using a sponge than by rinsing alone. Bacteria feeds on sugars in foods and drinks to produce acid, which erodes the surface of your teeth. Enamel on the tooth’s surface weakens at a pH of 5.5 and below. Wine has a pH of around 2 to 3 and Japanese sake also has a rather low pH, so the worst thing you can do after drinking is to fall asleep without brushing. Consuming lots of acidic foods and drinks weakens the surface of your teeth, causing decalcification that we call “tooth erosion.”

(M) So it’ s a good idea to drink water after consuming alcohol.

(K) Yes, it is. Carbonated beverages also have a low pH, so I can’t much recommend them from the viewpoint of protecting children’s teeth. Lemons and many other citrus fruits are also quite acidic. However, the human body is well designed to produce saliva – which has protective effects – when consuming acidic foods and drinks. That’s another reason we must make sure to chew well, since chewing produces saliva that helps encourage digestion. Research has shown that saliva is the most wonderful natural medicine. It’s important to keep your mouth clean so you can benefit from the effects of saliva.

(M) I see. That makes sense.

(K) We are currently focusing on extending the healthy life expectancy, which refers to the years in which people can live without being cared for. In 2018, the average life expectancy for Japanese men was 81.25 and for women was 87.32. The important thing is to be able to live healthfully – in other words, increasing healthy life expectancy.

(M) I think those who live long lives are the ultimate victors.

(K) Oral care is essential for increasing one’s healthy life expectancy.

(M) I’ve never heard the term “oral care” before.

(K) It means safeguarding the health of your mouth, mainly maintaining oral hygiene and oral functions. “Eating” is an important keyword. Classes at our university have implemented a food-related curriculum. In my classes, I train dentists who can talk about food based on the concepts that food is the source of life, food builds a health body, and that all kinds of sicknesses stem from “dirty” blood. The founder of NDU also believed in the importance of food, a way of thinking called “Shokuyodo.”

Japan’s food culture was refined over its long history

(M) So you look to Eastern medicine as well as Western medicine. I think it’s good to incorporate both, without depending overly on either.

(K) Mixing these two is the most efficient way. Japanese food is superb not only because it looks beautiful and tastes delicious, but also because elements such as the combinations of different ingredients have been refined over our long history. We serve grilled fish with grated daikon radish, which has sterilizing effects. The basic theory of Shokuyo says foods can be divided into “yin” and “yang.” Japanese people have mainly eaten grains, which are in the middle, rather than consuming meat. I feel some doubt about the theory that humans started out as hunters who mainly ate meat. I think our diet may have actually focused on grains. We have 20 molars, four canines, and eight incisors on the top and bottom. The ratio is 5:1:2. I think we can regard these as teeth for eating grains, meat, and vegetables.

(M) People would have needed a large number of hunters to catch enough game if meat was the only source of food. Food-related issues have limited the population, which increased suddenly when people became able to secure sufficient food through agriculture, including by growing rice. I think Japanese culture exists today because we could grow rice and were surrounded on all sides by oceans, so we had plenty to eat.

(K) I agree.

(M) Japan had a strong sense of solidarity, and a deep-rooted spirit of cooperation, because there has long been one ethnic group with one religion and one language. That’s what made Japan strong. I imagine a sufficient supply of food was another reason.

(K) Japanese people have smaller statures than Westerners, but our intestines are longer.

(M) Maybe that was better for digesting plants.

(K) Yes. Kanji (Chinese characters) are very logical. For instance, “腐,” (decay) is made by putting “肉” (meat) inside “府” (internal). I think this indicates the idea that meat did not suit the Japanese people.

(M) I do think it’s alright to eat some along with vegetables…

(K) If meat remains in the intestines for a long period of time, we think it is decomposed by bad bacteria, which makes it more toxic. They say that eating meat by itself makes the blood more acidic, leading to irritation and aggression. It seems nutritional science research was conducted in Western Europe until around 1885, and was centered in Germany. This research was apparently on the subject of how to build large physiques and increase aggression on the battlefield, and I think it must have focused on meat. We have no culture like this in Japan, where people have always been amiable.

(M) Conversely, we can say that Europeans ate meat as a way to survive.

(K) Yes. I am very impressed by the profound meanings behind kanji characters.

(M) The Japanese language is wonderfully expressive because it combines kanji, which are ideograms, with hiragana and katakana, which are syllabaries of phonetic symbols. That’s why we didn’t get in the habit of using many gestures like Westerners, who have to supplement their less-expressive languages.

(K) The character for food, “食,” is made up of “人” (person) and “良” (good), so it means “make people better.” “癌” (cancer) includes “食” (food) and “山” (a lot), so it can be interpreted as “a disease caused by eating too much.” This indicates that consuming an appropriate amount of food is the most important way of staying healthy. Kanji characters teach us many things. Going forward, I think dentists will do an essential job by discussing the importance of food.

(M) The high cultural level of Washoku, traditional Japanese food, is also worthy of mention. I love kaiseki cuisine that allows you to sample small amounts of different things.

(K) It’s also beautiful and well-balanced in terms of ingredients and nutrition. Actually, the most important thing is to eat a diet with plenty of minerals. Processed foods look nice, but they are all washed in factories so they lack minerals.

(M) I read a theory that says components leached from instant noodle containers have effects on the hormones of Japanese people, which causes more androgyny.

(K) I think that refers to styrene monomers, dimers, and trimers. Nothing leaches from instant noodle containers when you pour in 100°C water. However, styrene is oil-soluble, so it leaches out when the hot water is mixed with ingredients containing fat. I’ve heard major manufacturers are responding to this by taking gradual steps to ensure food safety.

(M) More people are talking about meat substitutes lately, too. They are expensive, but imitation “hamburgers” are said to have textures and tastes close to the real thing. They are apparently popular among vegetarians in the United States and Europe. Some of them, called “vegans,” don’t eat eggs or dairy products, either. I do have some concern that veganism isn’t a balanced diet… Some religions prohibit certain foods. Japanese people believe in “eight million gods,” so no foods are forbidden, unlike monotheistic religions. I think this is a unique characteristic of the Japanese, who value co-existence and co-prosperity.

(K) I think we have a balanced way of thinking for that reason.

Oral health affects the entire body, and periodontal disease is linked to dementia

(M) Tragic wars occur between monotheistic religions. The Crusaders were seen as heroes in the Christian countries, but surely they were nothing more than invaders from the Muslim standpoint. Many people are regarded as heroes because history is written by the victors. Americans talk about the “frontier spirit” like it’s something wonderful, but based on this they moved westward and massacred the Native Americans. As they pushed the frontier farther west, the Americans arrived at the Pacific Ocean and then advanced to Hawaii and the Philippines. Muslims are seen as cruel for reasons such as terrorist attacks, but the same is true of Christians if you look back at history. There were harsh struggles between Catholics and Protestants, and the Spanish also massacred indigenous peoples on the South American continent. These facts are covered up in the view of history determined by the victorious nations. The same thing has happened in Japan. Japanese people should learn more about what really happened, abandon the Tokyo Trials historical viewpoint implanted by the U.S., and feel pride in our country’s history. I am working to share the truth with people via activities such as the “True Interpretations of Modern History” Essay Contest and APA Japan Restoration Grand Prize. In any case, balance is certainly important in all things.

(K) Research on oral health spans even to the genetic level. The two major oral diseases not related to the functions of eating, talking, and drinking are periodontal disease and tooth decay. Today we know these have close connections with other diseases as well. For example, periodontal disease is related to ischemic heart disease, atherosclerotic disease, premature birth, low birth weight, aspiration pneumonia, rheumatism, and diabetes. Research is also underway across the world in recent years on the connections between periodontal disease and dementia.

(M) Dementia affects not only the patient, but also has major impacts on their family members and other people around them.

(K) Yes. According to a paper in Science, a famous academic magazine, periodontal disease causes inflammation in the brain that worsens Alzheimer’s-type dementia. If you lose your teeth and have to be put on a liquid diet, your ability to chew suffers. This worsens the body’s balance and makes you more likely to fall. Some research says dementia is caused by negative effects on the nerves of the hippocampus, which controls the memory.

(M) So working to prevent periodontal disease and tooth decay also helps guard against dementia. It seems like dentistry is changing from a type of medical care that fixes cavities by drilling teeth to one that cares for the entire body via the mouth.

(K) That’s right. The Basic Act on Measures for Strokes, Heart Disease, and other Cardiovascular Diseases to Prolong Healthy Life Expectancy was passed in the National Diet in December 2018. Article 2 of the supplementary provisions clearly states, “Research shall be performed on the connections between dental disease and cardiovascular disease.” We aren’t the only ones advocating the importance of oral health; research is being conducted as a national policy according to this law, which is founded on scientific data. I am currently working to give policy advice from the medical side. Up until now most of this advice has been from the government, but now we are saying the medical community must share its views to keep up with the times, and we are working to not only provide advice but also to see it realized. Right now, I am most focused on the theme of giving advice on health-related topics, and on having this advice be materialized, so medical care can contribute to society five or 10 years in the future. The Japanese Association for Dental Science is holding the Japanese dental industry’s largest event, which is put on once every four years, at Pacifico Yokohama in the City of Yokohama over three days from September 23, 2021. The theme is, “A Different Way of Thinking: The Dental Industry’s Challenge Towards 2040.” We are planning events such as public forums, including on the topic of extending the healthy life expectancy. I hope many people will attend.

(M) Japan was for many years centered on the extended family, but the nuclear family became the norm as one part of the postwar occupation policy by the U.S. Today there are more households made of individuals, and the saddest thing in Japan is those people who die alone and their skeletal remains are discovered later. No data is released on this, but I think they must number in the tens of thousands each year. I am sure there are many cases in which people died because they lived alone – if they had family, they might have been saved if someone called an ambulance. That’s why we should give tax incentives to revive the extended family, such as cutting property taxes to one half for homes with two generations and one third for homes with three generations. There would be many benefits. Besides preventing solitary deaths, this would also make it possible for families to pass down wisdom over the generations, strengthen family and regional solidarity, and allow for joyful lifestyles.

(K) I have some opinions about family structures, too.

Oral and intestinal health helps improve immunity

(M) Right now, the disease caused by the novel coronavirus (COVID-19) is causing turmoil around the world. All Japanese elementary, junior high, and high schools have been closed since March 2. In Japan the virus hasn’t been detected in all areas, so I wonder if closing all schools was the right thing to do. This will likely cause various types of problems, such as the parents who can’t go to work if their children are home. However, Prime Minister Shinzo Abe took a bold step by making this risky decision.

(K) I’m not sure if this political decision was right or wrong, but the global spread of this infectious disease is the worst since the 1918 Spanish flu pandemic. I think this will be an important experience to learn how to deal with future pandemics.

(M) On February 2, the U.S. banned all foreign nationals who had traveled to China in the past two weeks from entering the country. Japan only banned those who had stayed in the past 14 days in Hubei and Zhejiang Provinces, while allowing people from other parts of China, on February 13. I wonder if this is why the virus has spread in Japan. Also, the Diamond Princess is not a Japanese ship – it is a British-registered cruise ship operated by an American company. It just happened to be quarantined in the Port of Yokohama, which made it seem like the Japanese government was responsible for the high rate of infection. Maybe the ship should not have been permitted to dock. Today all of Asia is seen as a dangerous area, and fewer tourists are visiting Japan.

(K) Including what you have pointed out, I hope organizations will learn many things and reflect on what could have been done differently.

(M) Yes. There are also issues with the way news is being reported on COVID-19. More than 3,000 Japanese people die from influenza each year, but no information is released about who contracts it and where, and who ends up dying. In the past, 16,000 people used to die in car accidents every year. The number last year was 3,215. As of February 28, only five people have died of COVID-19 in Japan, excluding the deaths on the cruise ship. Many people have been infected and shown symptoms, but I’ve heard the ones who died already had diseases such as diabetes.

(K) The danger is very different depending on whether people have underlying conditions.

(M) People feel more peace of mind when presented with accurate data. More than 10,000 people have caught the virus in China, so they must be able to gather data on people in age ranges with a high risk of severity, their medical histories, etc. However, the Communist Party of China modifies disadvantageous data before releasing it, so there may be some doubts about its credibility… In my essay in the April edition of Apple Town, I wrote that the infection rate for Japanese people who returned home from Wuhan on four chartered flights was about 1.18%. Wuhan’s population is 11 million, so I predicted that roughly 130,000 must be infected. When I made this prediction, 15,000 people had the virus in Hubei Province, where Wuhan is located, but right now this number exceeds 60,000 and I suspect it will grow in the future.

(K) That’s possible.

(M) Pandemics caused by infectious diseases are the biggest risk in the hotel industry. People stop traveling for business or fun, and they also cancel parties and meetings, which causes major damage. The economy is slowing down due to the double-punch of COVID-19 and last October’s consumption tax hike.

(K) To discuss COVID-19 from the viewpoint of dentistry, I believe that intestinal bacteria provides resistance against viruses, which is the main source of human immunity. There are three types of intestinal bacteria: good bacteria, bad bacteria, and neutral bacteria. I believe the only way to increase good bacteria is to eat good food, like Japanese people have been doing since ancient times. Oral bacteria is also controlled by oral care. I’ve heard about a researcher who believes bad bacteria in the mouth is related to intestinal bacteria. I don’t catch the flu or colds because I make sure to eat well and perform oral care. Of course, I don’t get any vaccines, either.

(M) It’s important to eat three meals at set times, and also to stop eating just before you are full.

(K) Perhaps eating small amounts and doing physical labor are the keys to my health. For instance, if I eat too much on a given day, I make sure to eat less on the following day.

(M) I see. At the end of the interview, I always ask for a “word for the youth.”

(K) The name of NDA’s school is the “School of Life Dentistry,” not the “School of Dentistry.” I’m always telling students that we don’t just care for mouths – we care for the entire body, and for the lives of people. We think about health via dentistry. To bring up a personal health-related example, I never feel any stress. Or more accurately, I’ve erased this word from my vocabulary, maybe because I hate how conveniently it is used. I decided to try thinking of my work as a kind of ascetic training. Most toxic things that enter the body do so via the mouth and heart. I hope people will be interested in food and mental aspects as they think about health.

(M) Thank you for sharing such an interesting conversation with me today.

(K) Thank you.

Date of dialogue: February 28, 2020


Ryutaro Kobayashi

Born in Tokyo. After graduating from the Nippon Dental University’s (NDU) School of Dentistry, he earned his doctoral degree in the Graduate School of Dentistry. His specialty is dental surgery. In 2001 he became head of the Jaw Abnormality Diagnosis and Treatment Center at NDU’s School of Dentistry Hospital. He began working as a professor of dental surgery at NDU in 2010. He is currently director of NDU. He is involved in a wide range of activities to contribute to society on themes such as medical insurance, health, and food, including as councilor of the Japan Preventive Association of Life-style related Disease, chairman of the Japanese Association for Dental Science’s (JADS) Dental Treatment Council, general affairs director of the JADS, and managing director of the Japanese Dental Science Federation. In this way, he works to promote citizen health and vitalize the world of dentistry.