Human tooth

Human teeth are essential tools within the digestive system. They function to mechanically break down food through cutting and crushing. This process prepares food for swallowing and subsequent digestion. Teeth are embedded in the maxilla, which is the upper jaw, or the mandible, which is the lower jaw. These structures are covered by the gums to protect the area where the teeth meet the bone.

A tooth is composed of several distinct tissues with different densities. The visible part of the tooth is called the anatomic crown. This area sits above the cementoenamel junction, often called the neck. Below this junction lies the anatomic root, which is covered by a substance called cementum. Most of both the crown and the root consist of dentin. The dentin provides necessary support for the harder outer layers.

There are four primary types of teeth, each with a specific mechanical role. Incisors are used to cut food into smaller pieces. Canines are shaped to tear food apart. Premolars, also known as bicuspids, and molars are used to crush and grind food. In the permanent set, there are 32 teeth in total. This includes 16 teeth in the maxilla and 16 in the mandible.

Humans are diphyodont, meaning they develop two separate sets of teeth. The first set is known as deciduous teeth, or "baby teeth." These usually consist of 20 teeth and begin to erupt around six months of age. Some infants are even born with visible teeth, called natal teeth. The second set consists of 32 permanent teeth. These replace the deciduous teeth as the person grows.

Enamel is the outermost layer of the crown and is the hardest substance in the human body. It is 96% mineral, consisting mainly of a crystalline calcium phosphate called hydroxyapatite. Because it is so mineralized, enamel is very strong but also quite brittle. It can be up to 2.5mm thick at the cusp, but it is thinnest at the neck. Underneath the enamel lies the dentin. Dentin is a mineralized connective tissue that is softer and less brittle than enamel. It contains microscopic channels called dentinal tubules that radiate toward the pulp.

The innermost part of the tooth is the dental pulp. This is a soft connective tissue located within a pulp chamber. The pulp contains blood vessels and nerves that enter through a hole at the root apex. This tissue is often referred to as "the nerve" of the tooth. Surrounding the root is the cementum, a bone-like substance. Cementum helps the periodontal ligaments attach to the tooth for stability.

Tooth development is a complex process that begins during embryonic stages. Primary teeth start forming between the sixth and eighth weeks of an embryo. Permanent teeth begin to form around the twentieth week. Development follows four main stages: the bud stage, the cap stage, the bell stage, and maturation. During the bud stage, a collection of cells called a tooth germ forms. This germ includes the enamel organ, the dental papilla, and the dental follicle.

Dentists use specific systems to identify and number teeth for treatment. The FDI World Dental Federation notation is used globally. In the United States, the Universal Numbering System is the standard. An older method called the Palmer notation is still used by some in the United Kingdom. These systems allow professionals to describe specific teeth accurately. Understanding these structures and names is a key part of dental anatomy, a taxonomic science.