Norman Morgan, age 12tof Valley Station, Ky., for his question:
How is a tooth formed?
A new born baby is toothless, but deep within his jaws he has small wads of tissue called tooth buds. One set of these tooth buds will produce his baby milk teeth and another set will produce the permanent teeth which should last him a life time.
The part of a tooth which shows is called the crown, and it is covered with hard enamel to protect it from wear and tear. The roots of a tooth reach down to nerves and blood vessels deep in the jaw bone. The roots and the crown are joined by the neck of the tooth which is buried in the gums.
A little tooth bud begins by growing the hard crown of the tooth. This work goes on deep in the jaw and when it is finished the routs begin to grow. The roots push the crown up and up to the surface. When the roots are about two‑thirds grown, the crown is ready to break through, Baby has an uncomfortable day or two while the crown is cutting through the surface of the gum.
The first tooth, a lower front tooth, arrives when Baby is about six months old. Another lower and two upper front teeth arrive in the next few weeks. When he is about two yours olds, the young toddler has cut ten lower and ten upper teeth. This is his quota of primary teeth, also called milk teeth or deciduous ‑ which means falling out ‑ teeth. They will last him until he reaches first grade.
Meantime, other tooth buds in the jaw are preparing a set of permanent teeth. These tooth buds are situated deep in the jaw, below the roots of the milk teeth. A new permanent tooth also begins to form with the crown. It becomes very hard and as it grows it begins to push up the coats of the milk tooth, making it come loose. Two pairs of back teeth loosen first, when the young person is around six years of age.
As the roots of the permanent tooth grow, tooth‑making material is taken from the roots of the old milk tooth. This useful material is absorbed by the jaw and, when the old milk tooth is ready to come out, it may be only a crown sitting on the gum. Because of this, some people think that milk teeth have no roots at all: Actually, they have roots for a number of years but they dissolve away as the permanent teeth develop.
After the two pairs of back teeth have grown ins the front teeth begin to show signs of change. The milk teeth fall out one at a time and two upper and two lower permanent teeth grow in to replace them. By the time he is about 13, a young person has twenty eight permanent teeth and this is all for a while. Between the ages of 17 and 21 he will grow a third molar tooth at the back of each jaw, top and bottom. These are the so‑called wisdom teeth and they bring the number of permanent teeth up to 32.