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 day was established in 1928 by the Japan Dental Association, giving it a history of roughly 100 years. The week from June 4th to 10th is also designated "Dental and Oral Health Week," during which awareness campaigns about dental and oral health are held across the country.

A History of the Observance

The Japan Dental Association, founded in 1926, held its first "Cavity Prevention Day" on June 4, 1928, with the goal of improving the nation's oral hygiene.

• 1928: The Japan Dental Association establishes and begins observing "Cavity Prevention Day."
• 1939–1941: Renamed "Tooth Protection Day," continuing as part of wartime public health campaigns.
• 1942: Held as the "National Health Cavity Prevention Campaign."
• 1943–1947: Suspended during the war.
• 1949: Revived as "Oral Hygiene Week" (June 4th–10th).
• 1958: Renamed "Cavity Prevention Day."
• 1993: Renamed "Dental and Oral Health Week," 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 a habit of brushing within three minutes after every meal, 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: Visit the dentist every three to six months 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, and the Japan Dental Association jointly run nationwide awareness campaigns calling for the prevention, early detection, and early treatment of dental conditions. Events, consultations, and checkups are held at dental clinics, schools, and health centers across the country.