A tooth is a hard, calcified, bone-like structure set in the jaw. Teeth are used for biting and chewing as well as forming words. Posterior teeth are the teeth set on both sides of the back of the jaws. These teeth are called molars and bicuspids.
Teeth can be divided into two parts and three layers. The parts of the tooth are the crown, or the top of the tooth that appears above the gum line, and the root, or the part of the tooth that holds the tooth in place in the jawbone. A tooth has a hard layer on the outside to help protect the tooth from being damaged called enamel. Dentin is located below the enamel and serves as a secondary level of protection. Pulp is the soft, interior part of a tooth that includes those nerve endings that can cause pain and the tooth's blood supply.
Human beings usually have two sets of teeth — deciduous teeth and permanent teeth. Deciduous teeth are sometimes called baby teeth or primary teeth. Permanent teeth can be referred to as adult teeth.
Deciduous teeth start to grow when a baby is about six months old until the child is about two and a half years old. By the age of two and a half, the child should have 0 teeth. Between the ages of six and 12, children start to lose deciduous teeth as their permanent teeth start to push towards the surface of the gums.
Permanent teeth are called permanent because most people don't have a third tooth to replace a permanent tooth in the event that a permanent tooth is lost or damaged. People usually have a total of 32 teeth in their mouths. Most people grow their last permanent teeth between the ages of 18 and 25.
Adult posterior teeth include three molars and two bicuspids on the upper and lower jaws and on both sides of the jaws for a total of 20 teeth. The three molars going from the outside of the jaw towards the inside are called the third molar or the wisdom tooth, the second molar and the first molar. Continuing moving inwards on the jaw, the first molar is followed by second bicuspid and the second bicuspid is next to the first bicuspid, completing the posterior teeth.
The mouth has anterior teeth in addition to posterior teeth. Anterior teeth include the cuspid, the lateral incisor, and the central incisor. The purpose of anterior teeth is to cut or tear food while the posterior teeth are used to grind and chew a meal.