Ellin Bessner, age 10, of Montreal, Quebec, Canada, for her question:
How can teeth grow from the gums?
The tough teeth seem to sprout from the soft pink gums and sturdy nails seem to grow from the soft flesh at the stips of toes and fingers. However, the hard materials in teeth and nails are created behind the scenes. We see them only when they grow big enough to poke up to the surface. Nails, of course, go on growing all our lives. But we get only two sets of teeth.
Our tooth growing centers are wads of special cells, buried down inside the jawbones. They are called tooth buds and they form even before a person is born, no doubt because their complicated work must be done very slowly and correctly. Each bud inherits a blueprint, a built in pattern to follow. It must be able to select the right tooth building ingredients and arrange them to make durable materials, molecule by molecule.
Since teeth come in different sizes, shapes and places, each bud must follow its own pattern. Only 20 of them build first or primary teeth. The correct building materials must be right there, in the blood and other liquids inside the body. The buds select calcium and other suitable molecules from our digested food. They cannot use such items as sugary candies. But they can build splendid teeth from materials in milk, salads and assorted vegetables.
The primary teeth are the right size to fit the young, growing jaw bones. If they were very sturdy, removing them for the really big job would be a problem. The buds begin this preparation while the primary teeth are still in their places. Down in the jawbones they start building the tough crowns for the durable permanent teeth. When each crown is completed and coated with shiny enamel, a bud begins to build the roots. As they grow, they push the crown up through the gums and out into the light of day.
The buds work as a team and complete their teeth on schedule, more or less in matching pairs. When a person is about six, the first pairs of molars appear. Often the primary teeth they replace fall out easily and seem to have no roots at all. This is because their ingredients were dissolved and the buds used them to build more durable replacements. However, most of the building ingredients come from foods on the daily menu.
Meantime, down in the jaws, the crowns for other teeth are in various stages of completion. From the front incisors are pushed through the gums. At 13, a person has 28 permanent teeth and the tiresome task still to be finished. However, there are four more tooth buds and these slow pokes are preparing a surprise. We may not hear from them for many years. But sometime after a person is 17, four more molars called wisdom teeth appear one at each corner near the jaw hinges.