Primary Teeth

The development of primary teeth begins while the baby is in the womb. At about 5 weeks' gestation, the first buds of primary teeth appear in the baby's jaws. At birth, the baby has a full set of 20 primary teeth (10 in the upper jaw, 10 in the lower jaw) hidden under the gums. Primary teeth are also known as baby teeth, milk teeth or deciduous teeth.

Permanent Teeth

Permanent teeth are also known as adult teeth or secondary teeth. The permanent teeth start to develop in the jaws at birth and continue after a child is born. By about 21 years, the average person has 32 permanent teeth, including 16 in the upper jaw and 16 in the lower jaw. (In some cases, the third molars – commonly called wisdom teeth – do not develop or do not erupt so some people only have a set of 28 permanent teeth.)