page_title: Tooth
section_title: Fish
hierarchical_section_title: Tooth / Fish
caption_attribution_description: English: A great white shark at Isla Guadalupe, Mexico. The picture is a digital copy of my old film picture.
context_page_description: A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the embryonic germ layer, the ectoderm.
  The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw.
  Some animals develop only one set of teeth while others develop many sets. Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length.
context_section_description: Fish, such as sharks, may go through many teeth in their lifetime. The replacement of multiple teeth is known as polyphyodontia.
  A class of prehistoric shark are called cladodonts for their strange forked teeth.
caption: Teeth of Great White Shark
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