Jim Chambers, age 12, of Denton, Texas, for his question:
HOW MANY TEETH DO WE HAVE?
Every person grows two sets of teeth. The first, called primary, baby deciduous or "milk" teeth, appear when a baby is from about 6 to 30 months old. The second set, which are permanent teeth, comes in from about the age of 6 years to the early 20s.
There are 20 primary teeth and 32 permanent teeth.
An infant seems to have no teeth when born, but hidden in the baby's gums are the seeds or buds of all the primary teeth, as well as those of four permanent molars. The teeth actually start to form about seven months before the baby is born.
As the infant grows, the teeth start to form around the buds. Deposits of calcium from food, particularly milk, gradually build and harden to form the body and coverings of the teeth. The deposits develop in layers or rings, much like the layers that form the rings of a tree trunk.
The first primary teeth to push through the gums are the incisors. These are the cutting, biting or shearing teeth. They grow in the front center of the jaw.
Then, in order, come the first molars, the canines and the second molars.
The pushing through of primary teeth, called teething, sometimes causes an infant some discomfort. But this discomfort doesn't last too long.
The first permanent teeth to appear are the first, or six year molars. Then come the incisors, the canines, the bicuspids and the second and third molars.
Incisors are the eight permanent front teeth with four in the upper jaw and four in the lower. The upper incisors usually slightly overlap with lower ones. This allows the rear teeth to come in close contact.
When all the primary teeth have grown in, children should start to visit a dentist regularly for examinations, preventive measures or treatments.
It is then important that regular visits to the dentist continue for the rest of a person's life.
In your permanent teeth, canines or cuspids are next to the incisors. They are sometimes called "eyeteeth" or "dogteeth." One of these four teeth grows at the right and one at the left of the four incisors of each jaw. These strong teeth have long, heavy roots and cusps, or pointed biting surfaces. The canines tear large pieces of food into smaller ones.
Bicuspids, or premolars, grow next to the canines. There are eight of these teeth, two next to each of the canines. Each premolar has two cusps and may have one or two roots. The premolars crush food into even smaller pieces.
Molars are the 12 teeth farthest back in the mouth. Three of them grow on each side of the upper and lower jaws. The third molars are sometimes called wisdom teeth, because they usually appear during late adolescence or early adulthood.
Molars may have two or three roots and several cusps. They provide a strong, broad surface for grinding pieces of food into tiny bits.