Deciduous And Permanent Teeth and Structure of a Tooth

Teeth are important accessory digestive structures that mechanically break food into smaller pieces during mastication (mas-ti-ka’-shun), or chewing. Humans develop two sets of teeth: deciduous and permanent teeth.

• Enamel: It is the hardest bodily tissue that covers the surface of the dental crown. It is as hard as crystal (7 on the Mohs scale of mineral hardness).
• Dentin: The tissue that is responsible for formation of the tooth from the dental crown to the tooth root, situated inside the enamel and cementum. It is softer as compared to the enamel. A tissue fluid named the denital tubule is filled in small tube which runs inside the dentin.
• Cementum: The tissue that covers the surface of the tooth root. It uses periodontal ligament as  a connection between the alveolar bone and the tooth . Its hardness is similar to bone.
• Dental pulp: The tissue is called the nerve. Blood vessels and the lymph vessels, as well as nerve fibers, are located in the dental pulp, supplying nutrients to the dentin.
• Periodontal ligament: Tissue that consists mainly of the fibrous tissue that acts as a connection between the tooth root and the alveolar bone. It’s a kind of barrier that prevents force applied to the tooth from being directly imposed on the alveolar bone while chewing food.
• Alveolar bone: The jaw bone supporting the tooth; the tooth is planted into this bone. When a large part of the alveolar bone is destroyed by periodontal disease or other causes, the tooth becomes loose.
• Gingiva: Commonly known as “gum”, gingiva is the soft tissue that covers the alveolar bone.
• Gingival sulcus: The small space between the tooth and the gums. Even people with healthy teeth usually have a depth of 1 to 2 mm in this space. When this space deepens due to inflammation, it is called the periodontal pocket or gingival pocket.

The deciduous teeth, the first set, start to erupt through the gums at about six months of age. Central incisor (in-si-zers) teeth come in first, and second molar teeth erupt last. There are 20 deciduous teeth, 10 in each jaw, and all of them are in place by three years of age. Deciduous teeth are gradually shed starting at about six years of age, and they are usually lost in the same order in which they emerged.

The permanent teeth begin appearing at about six years of age when the first molar teeth (six-year molar teeth) erupt. All of the permanent teeth, except the third
molar teeth, are in place by age 16. The third molar teeth (wisdom teeth) erupt between 17 and 21 years of age, or they may never emerge. In many persons, there is insufficient room for the third molar teeth, so they become impacted and often must be surgically removed. The 32 permanent teeth, 16 in each jaw, consist of four different types: incisor teeth, canine teeth, premolar teeth, and molar teeth.

The chisel-shaped incisor teeth are adapted for biting off pieces of food. The canine teeth are used to grasp and tear tough food morsels. The somewhat flattened surfaces of the premolar teeth and molar teeth are used to crush and grind food.

Each tooth consists of two major parts: a root and a crown. The crown is the portion of the tooth that is exposed and not covered by the gingiva (jin-ji-vah), or gum, covering the underlying bone. The root is embedded in a socket, called an alveolus. A hard substance called cement attaches the root, through tough periodontal ligaments, to the alveolus. The junction of the crown and root is known as the neck of the tooth.

Most of a tooth is composed of dentin, a hard, bonelike substance. The crown of the tooth has a layer of enamel overlying the dentin. Enamel is the hardest substance in the body and it is appropriately located to resist the abrasion caused by chewing hard foods. Each tooth is supplied with blood vessels and a nerve, which enter the tip of a root and pass through a tubular root canal into the pulp cavity of the crown, a central space in the crown of a tooth. Together the pulp cavity of the crown and the root canal form the pulp cavity of the tooth. In a molar tooth, the pulp cavity of the crown is relatively large and roughly box-shaped. But in a canine tooth, the pulp cavity of the crown is an elongated enlargement of the root canal. Dental pulp is soft areolar connective tissue that fills the pulp cavity and supports the blood vessels and nerves.

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