Why children around the world wish for a mouse's teeth
Across India, Korea, Nepal and Vietnam, children toss a lost tooth onto the roof or under the floor and ask for a mouse's tooth in return, because rodent teeth never stop growing. Humans get only two sets, and the first begins forming just six weeks into embryonic development.
Baby teeth start as a band of tissue called the dental lamina around the sixth week, and by eight weeks the embryo has ten buds on each arch. The full set is twenty teeth, five in each quarter of the mouth: two incisors, a canine and two molars. Teething usually starts near six months, beginning with the lower front incisors, and finishes between 25 and 33 months with the upper second molars. Most mammals share this two-set pattern, though elephants, kangaroos and manatees keep replacing teeth throughout life.
Replacement is a quiet demolition job. As an adult tooth rises, it presses on the root above it, and cells called odontoclasts dissolve that root so the old crown loosens and falls out, normally without pain or bleeding. Shedding runs from about six to twelve, and by thirteen most children have only permanent teeth. The two baby molars are not replaced by molars at all but by premolars. When a successor never forms, a baby tooth can keep working well into adulthood.
These temporary teeth do lasting work. They hold space in the jaw, guide adult teeth along their eruption paths and shape the growth of jaw muscles and bone, as well as helping with speech and chewing. Decay spreads through them quickly and often reaches the pulp. One gentle repair, the Hall Technique, presses a preformed metal crown over a decayed tooth with no drilling or local anaesthetic, and studies found fewer failures and less discomfort than with conventional fillings, though only in healthy children.
Folklore around lost teeth is remarkably varied. English speakers leave teeth for the tooth fairy, while France and French-speaking Belgium have a little mouse and Spanish tradition has Ratón Pérez. Children in Turkey, Cyprus and Greece throw teeth onto the roof with a wish. In Japan upper teeth go straight down and lower teeth straight up so new ones grow in straight, and Hausa custom warns a child not to let a lizard glimpse the gap.
Source: Deciduous teeth
