Teeth are made up of different layers — enamel, dentin, pulp, and cementum. Enamel, which is the hardest substance in the body, is on the outside of the tooth. The second layer is dentin, which is softer than enamel, and the deepest layer inside the tooth is pulp, which consists of nerves and blood vessels. Cementum is on the root of the tooth and is beneath the gums.

The number and types of teeth a person has changes as they age. Typically, people have two sets of teeth during their life — primary, or baby teeth, and permanent, or adult teeth. In this article, we look at the teeth that children and adults have, as well as their functions.

Humans have the following types of teeth:
<h3>Incisors</h3>
Incisors are the sharp teeth at the front of the mouth that bite into food and cut it into smaller pieces. They are flat with a thin edge. They are also called anterior teeth.

Both children and adults have eight incisors — four central incisors at the front of the mouth, two on each row, with one lateral incisor positioned on either side of them.
<h3>Canines</h3>
Canines are the sharp, pointed teeth that sit next to the incisors and look like fangs. Dentists also call them cuspids or eyeteeth. Canines are the longest of all the teeth, and people use them to tear food.

Both children and adults have four canines. Children usually get their first permanent canines between the ages of 9 and 12. The lower canines tend to come through slightly before those in the upper jaw.
<h3>Premolars</h3>
Premolars, or bicuspids, are bigger than the incisors and canines. They have many ridges and help chew and grind up food. Adults have eight premolars. The first and second premolars are the molars that sit next to the canines.

Young children do not have premolar teeth. These first appear as permanent teeth when children are 10–12 years old.
<h3>Molars</h3>
Molars are the biggest of all the teeth. They have a large, flat surface with ridges that allow them to chew food and grind it up. Adults have 12 permanent molars — six on the bottom and top jaw, and children have eight primary molars.

The last molars to erupt are wisdom teeth, or third molars, which usually come through between the ages of 17–21. These sit at the end of the row of teeth, in the far corners of the jaw. Some people do not have all four wisdom teeth, or the teeth may stay unerupted in the bone and never appear in the mouth.

Sometimes wisdom teeth can become impacted, which means they can become trapped under the gum and are unable to come through properly.

Wisdom teeth that only come through halfway or are in the wrong position can increase the risk for infection or damage in surrounding areas. It is essential to see a dentist if people have any issues with their wisdom teeth.

People may experience mild discomfort when their wisdom teeth start pushing through the gums, but anyone feeling a lot of pain or has swelling should see a dentist.

A dentist may need to remove wisdom teeth if a person has tooth decay, pain, or an infection. People do not need these teeth for chewing, and they are difficult to keep clean because of their position far back in the mouth.
<h3>Number of teeth</h3>
Children have 20 primary, or baby, teeth. Primary teeth first start to appear when babies are around 6 months old. Children usually get all their primary teeth by the age of 3.

These teeth gradually fall out, and 28 permanent teeth replace them. Sometimes, permanent teeth push the baby teeth out, but typically, permanent teeth come through the gums at the back of the mouth behind the last baby tooth in the jaw.

The first permanent teeth to erupt through the gums are four first, or '6-year' molars, so-called because they usually come through when a child is about 6 years old.

The first baby teeth to fall out are the lower central incisors. The adult central incisors tend to erupt around the same time as the first permanent molars around age 6-7.

Usually, people have lost all of their baby teeth by around the age of 14.