Human teeth

Human teeth

Humans have 4 types of teeth: incisors, canines, premolars and molars.

Biology

Keywords

teeth, tooth, dentition, permanent tooth, deciduous tooth, incisor, canine, molar, premolar, crown, pulp chamber, tooth neck, enamel, dentine, gum, tooth root, cement layer, diphyodont dentition, tooth type, human, biology

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Teeth

  • molars - They are found at the back of the mouth. Adults have 4-6 molars in both jaws, 8 to 12 in total.
  • premolars - They are used for cutting and crushing food. Humans have 4 premolars in both jaws, 8 in total.
  • canine tooth - Human canine teeth are relatively small, while those of predatory animals are usually very large. There are two canines in both jaws, 4 in total. Canine teeth serve to grip and tear food.
  • incisors - They are found in the front of the mouth and are used for shearing or cutting food (that is, biting). Humans have four incisors in each jaw, 8 in total.

Human teeth have various shapes and functions. The four lower and four upper incisors are used for shearing or cutting food into chewable pieces so they have a blade-like shape. The lower incisors are relatively long and narrow, while the upper incisors are wider.

There are two lower and two upper canines next to the incisors. These teeth are cone-shaped and pointed. Canines serve to grip and tear food.

The 4 pairs of premolars, left and right to the canines, have a wide chewing surface. The function of these teeth is to cut and crush food to smaller pieces before transferring them to the molars.

The molars, which serve to grind the food, (that is, to chew it) are located at the back of the dentition. Their chewing surface is even larger than that of premolars. Humans have 8-12 molars in total. The backmost ones, commonly called 'wisdom teeth', usually erupt between the ages of 17 and 25, although in some people they none, or not all of them erupt.

Longitudinal section

  • crown - The part of the tooth not embedded in the gum.
  • neck - The part of the tooth between the root and the crown.
  • root - The part of the tooth embedded in the gum.
  • enamel - A white, translucent substance that covers the crown of the tooth. The enamel does not contain blood vessels or nerves; it absorbs minerals from food. It is the hardest tissue in the human body.
  • dentine - A porous, bone-like tissue; the most substantial component of teeth.
  • cementum - A thin layer of bone-like tissue that covers the root.
  • dental pulp - It is made up of living connective tissue and odontoblast cells and contains blood vessels and nerves. A toothache is caused by the irritation of those nerves. Inflamed pulp tissue is usually removed by root canal treatment.
  • gum - A mucous tissue that covers the bones into which the teeth are fixed.
  • bone

The teeth sit in bony sockets within the jawbones, which are called dental alveoli.
Teeth consist of three main parts. The root anchors them in the sockets. Teeth have one or more roots. The visible part of the teeth is called the crown. The part between the crown and the root is called the neck.

The root is covered by cementum, while the crown is covered by tooth enamel, the hardest substance in the human body. It is a highly mineralised substance, the primary mineral being hydroxyapatite. It is very brittle, so if a cavity is formed underneath, it easily breaks during chewing.

Dentine is a porous bone-like tissue, less hard but more flexible than the enamel. It has a high organic content, therefore it is more susceptible to decay then cementum. Dental pulp, located in the pulp chamber and pulp canals, is made up of living connective tissue and odontoblast cells and contains blood vessels and nerves. Odontoblast cells produce dentine.

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Oral cavity

  • teeth - Humans have 20 milk teeth during infancy. The number of permanent teeth is 28-32.
  • tongue - A muscular organ with a characteristic shape. It plays an important role in chewing, forming a bolus, as well as in speech and the formation of some facial expressions.
  • gum - A mucous tissue that covers the bones into which the teeth are fixed.
  • hard palate - A bony plate covered with mucous membrane at the front of the roof of the mouth.
  • soft palate - The soft tissue that forms the back of the roof of the mouth. It separates the oral cavity from the nasal cavity.
  • uvula - A conic projection at the back of the soft palate, covered by mucous membrane. Its primary function is to prevent food from entering the nasopharynx.
  • vestibule - The part of the oral cavity found between the teeth and the cheeks.

The nutrient content of solid foods is not readily accessible, therefore it is necessary to mechanically crush the food before chemical breakdown can start. This is the job of our teeth.

The tongue also plays an important role in chewing: as it moves in the oral cavity, it presses the food against the chewing surface of the teeth.
Chewing is closely related to swallowing. Almost all the components found in the oral cavity are involved in these two processes.

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