Cavity Prevention Day (Mushiba Yobou Day)

What is Cavity Prevention Day?

June 4th is "Cavity Prevention Day" (Mushiba Yobou Day) in Japan. The date comes from a play on numbers: "6" can be read as "mu" and "4" as "shi"—together sounding like "mu-shi," which is part of "mushiba," the Japanese word for "cavity" or "tooth decay." The Japan Dental Association held Cavity Prevention Day on June 4th from 1928 to 1938. Its successor today is "Dental and Oral Health Week" from June 4th to 10th, during which awareness campaigns about dental and oral health are held across the country. In response to calls for its revival, the Japan Anniversary Association also re-established June 4th as "Cavity Prevention Day" in 2001.

A History of the Observance

The Japan Dental Association held its first "Cavity Prevention Day" on June 4, 1928, with the goal of improving the nation's oral hygiene. It has since been carried on under different names and forms, leading to today's Dental and Oral Health Week.

• 1928-1938: The Japan Dental Association holds "Cavity Prevention Day" on June 4th.
• 1939–1941: Held as "Tooth Protection Day" (May 4th).
• 1942: Held as the "National Health Cavity Prevention Campaign."
• 1943–1947: Suspended.
• 1949: Revived as "Oral Hygiene Week."
• 1952: Held as the "Oral Hygiene Promotion Campaign," returning to "Oral Hygiene Week" in 1956.
• 1958: Becomes "Dental Hygiene Week," run by the Ministry of Health and Welfare, the Ministry of Education, and the Japan Dental Association.
• 2001: The Japan Anniversary Association re-establishes June 4th as "Cavity Prevention Day" to promote the importance of preventing cavities.
• 2013: Renamed "Dental and Oral Health Week" for the first time in about 50 years, the name still used today.

How Cavities Form

A cavity (dental caries) develops when bacteria living in the mouth—primarily Streptococcus mutans—break down sugars from food and produce acid, which dissolves the tooth. As a cavity progresses, it eats through the enamel, then the dentin, and eventually reaches the pulp (nerve), causing severe pain and potential tooth loss.

• Causative Bacteria: Streptococcus mutans and similar bacteria ferment sugar to produce organic acids.
• The Effect of Sugar: Refined sugar (sucrose) in particular is easy for bacteria to use, raising cavity risk.
• The Role of Saliva: Saliva has a buffering effect that neutralizes acid, as well as a remineralizing effect that can repair early-stage demineralization of the teeth.

How to Prevent Cavities

• Proper Brushing: Make careful daily brushing a habit, and use interdental brushes or floss to clean between the teeth.
• Using Fluoride: Fluoride toothpaste and mouthwash promote remineralization of the teeth and boost cavity prevention.
• Managing Sugar Intake: Cut back on sugary drinks and snacks, especially eating or drinking right before bed.
• Regular Checkups: Get regular checkups at your dentist for early detection and treatment.
• Dental Sealants: Filling the grooves of children's molars with resin is a preventive treatment that helps keep food debris from getting trapped.

Cavities in Japan Today

Japan was once known as a country with a very high rate of cavities, including among 12-year-olds. In recent years, however, the spread of preventive dentistry, the use of fluoride, and changes in eating habits have led to a major decline in cavities among children. On the other hand, cavities in adults and the elderly—including secondary cavities and root cavities—remain an ongoing challenge.

Dental and Oral Health Week (June 4th–10th)

The week from June 4th to 10th is "Dental and Oral Health Week" in Japan. The Ministry of Health, Labour and Welfare, the Ministry of Education, Culture, Sports, Science and Technology, the Japan Dental Association, and the Japan School Dental Association run nationwide awareness campaigns calling for the prevention, early detection, and early treatment of dental conditions. Events and consultations are held across the country.