Finland is poor in selenium. Selenium deficit leads to muscular dystrophy in animals. Since 1962, selenium has been added in Finland to some animal foodstuffs, since 1968 to all animal foodstuffs. Addition of selenium to fertilizers started in 1984. Intake of selenium by man and cattle today is roughly 1.0 times higher than it was before selenium supplementation. Collagen is the most important component of the organic matrix of the tooth. Selenium can replace sulphur in bonds of collagen. The resulting bond is stronger than a sulphur bond. Since selenium supplementation, the conditions of the teeth of children and young people has improved considerably. The author believes that selenium supplementation has reduced the incidence of caries in young Finns.