Tooth Development, Permanent Health Article

Definition

Permanent teeth, which are also known as adult teeth, are the second and final set of teeth in the human mouth. There are generally 32 permanent teeth in an adult mouth—16 in the upper jaw and 16 in the lower jaw. The permanent teeth replace the 20 primary teeth, which are also known as baby teeth, milk teeth, or deciduous teeth.

Description

In the mouth, a combination of hard and soft tissue areas form the occlusion (bite). The teeth, along with upper and lower jaw bones, are among the hard tissues. The soft tissue includes the gums, tongue, and salivary glands.

Teeth, both primary and permanent, are used to chew and swallow food. Each tooth is divided into a crown and root. The crown is visible. The root grows below the gum and is attached to the jawbone. A pulp chamber located in the center of the crown houses pulp tissue.

The crown is covered with enamel, the hardest substance in the body. It is 95% calcified (mineralized). Cementum, a thinner material, surrounds a portion of the root.

Types of teeth

The shape of the crown determines the purpose of the tooth:

• Incisors have a straight edge to incise or cut food. The two central incisors in each jaw are also known as the front teeth, indicating their location in the mouth. A lateral incisor is located on each side of the front teeth. There is one root in each incisor.
• The canine teeth are located in the corners of the mouth, with two in each jaw. The canine teeth have pointed crowns and are longer than the other teeth. These teeth are used to grip and tear food. They are also known as cuspids or eye teeth. Each canine tooth has a single heavy root.
• On each side of the six front teeth (incisors and canines) are five molars known as the back teeth. The crowns have wider surfaces that are used to chew food. On the surface of the molar are two or more cusps, slight elevations in the crown that are used to grind and pulverize food before it is swallowed.
• The premolars, which are also known as bicuspids, are located behind the cuspids (canine teeth). They help the canine teeth to grip and tear food. There are eight premolars in the adult mouth, with half in the upper jaw and half in the lower jaw. A premolar has one or two roots.
• The remaining molars in each jaw are used to grind food. The first molar, also known as the six-year molar, is adjacent to the second bicuspid. On the other side of the first molar is the second molar, the twelve-year molar. At the back of the mouth are the third molars, which are also known as wisdom teeth. The upper molars generally have three roots, and there are usually two or three roots in the lower molars. These roots help bolster the teeth for the heaviest pressure of chewing and grinding food.

Permanent tooth development

The development of both primary and permanent teeth starts long before these teeth are visible. When a child is born, the primary teeth are partially formed, and development of permanent teeth has started in the jaw bone.

At about the age of six, a child begins losing primary teeth and permanent teeth erupt (appear). The primary teeth fall out (exfoliate) to make room for the permanent teeth to erupt. Generally, girls' teeth develop before boys, and lower teeth grow through the gums before upper teeth. Development of this second set of teeth can sometimes continue into adulthood. A delay in the development process of two years or more could be a symptom of hormonal deficiencies.

TOOTH DEVELOPMENT IN THE UPPER JAW. According to the American Dental Association (ADA), permanent teeth in the upper jaw generally erupt in this order:

• Between the ages of 6 and 7, the permanent first molars erupt. These teeth erupt behind the child's primary second molars.
• Between the ages of 7 and 8, central incisors appear.
• Lateral incisors erupt between the ages of 8 and 9.
• Between the ages of 10 and 11, the first premolars (first bicuspids) appear.

• The second premolars appear between ages of 10 and 12.
• Between the ages of 11 and 12, the canine teeth (cuspids) erupt.
• Between the ages of 12 and 13, second molars erupt.
• Between the ages of 17 and 21, the molars known as wisdom teeth appear.