Tooth

A tooth (pl.: teeth) is a hard, <a href="/facts/Calcification/NRSv3tMS">calcified</a> structure found in the <a href="/facts/Jaw/6a11Csjh">jaws</a> (or <a href="/facts/Mouth/WthDlXsC">mouths</a>) of many <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a> and used to <a href="/facts/Mastication/DdgB4W6f">break down</a> <a href="/facts/Food/RgNq6NAK">food</a>. Some animals, particularly <a href="/facts/Carnivore/q6h6aSqe">carnivores</a> and <a href="/facts/Omnivore/b8zcsuJF">omnivores</a>, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by <a href="/facts/Gingiva/4JhxlckG">gums</a>. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic <a href="/facts/Germ_layer/eSUTuH7F">germ layer</a>, the <a href="/facts/Ectoderm/lg5p0jTL">ectoderm</a>.
The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The <a href="/facts/Mammal_tooth/dfKW4lQI">teeth of mammals</a> have deep roots, and this pattern is also found in some fish, and in <a href="/facts/Crocodilian/G4LbxJs6">crocodilians</a>. In most <a href="/facts/Teleost/1YULPGW5">teleost</a> fish, however, the teeth are attached to the outer surface of the bone, while in <a href="/facts/Lizard/VPCpCwjT">lizards</a> they are attached to the inner surface of the jaw by one side. In <a href="/facts/Cartilaginous_fish/xcW7PJDU">cartilaginous fish</a>, such as sharks, the teeth are attached by tough <a href="/facts/Ligament/xAf6lB1z">ligaments</a> to the hoops of <a href="/facts/Cartilage/vxy2qzKN">cartilage</a> that form the jaw.
Monophyodonts are animals that develop only one set of teeth, while <a href="/facts/Diphyodont/yylqyXCG">diphyodonts</a> grow an early set of <a href="/facts/Deciduous_teeth/CJPbq2se">deciduous teeth</a> and a later set of <a href="/facts/Permanent_teeth/76MtaDgv">permanent or "adult" teeth</a>. <a href="/facts/Polyphyodont/RPQeED6Y">Polyphyodonts</a> grow many sets of teeth. For example, <a href="/facts/Shark/rh5Cotvx">sharks</a>, grow a new set of teeth every two weeks to replace worn teeth. Most extant mammals including humans are diphyodonts, but there are exceptions including elephants, kangaroos, and manatees, all of which are polyphyodonts.
<a href="/facts/Rodent/mT4m8QJq">Rodent</a> incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the <a href="/facts/Beaver/uoJ2xU4D">beaver</a> is due in part to this qualification. Some rodents, such as <a href="/facts/Vole/yPC6PvYk">voles</a> and <a href="/facts/Guinea_pig/gRXC2qNN">guinea pigs</a> (but not <a href="/facts/Mouse/6m1X7m0g">mice</a>), as well as <a href="/facts/Lagomorpha/0J5JT196">lagomorpha</a> (<a href="/facts/Rabbit/8jQGWcQD">rabbits</a>, <a href="/facts/Hare/a3Pg06T3">hares</a> and <a href="/facts/Pika/4VMuW8TH">pikas</a>), have continuously growing molars in addition to incisors. Also, <a href="/facts/Tusk/FovweWbM">tusks</a> (in tusked mammals) grow almost throughout life.
Teeth are not always attached to the jaw, as they are in mammals. In many <a href="/facts/Reptile/04n1uKf1">reptiles</a> and fish, teeth are attached to the <a href="/facts/Palate/o0RMlkss">palate</a> or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some <a href="/facts/Teleost/1YULPGW5">teleosts</a> even have teeth in the <a href="/facts/Pharynx/51F3eVms">pharynx</a>. While not true teeth in the usual sense, the <a href="/facts/Dermal_denticle/MS2brwuo">dermal denticles</a> of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in the more primitive <a href="/facts/Jawless_fish/LohAXfEH">jawless fish</a> – while <a href="/facts/Lamprey/nxgTvh0z">lampreys</a> do have tooth-like structures on the tongue, these are in fact, composed of <a href="/facts/Keratin/tBh0bY47">keratin</a>, not of dentine or enamel, and bear no relationship to true teeth. Though "modern" teeth-like structures with <a href="/facts/Dentine/UMpkJ3UV">dentine</a> and <a href="/facts/Tooth_enamel/ffUMmssl">enamel</a> have been found in late <a href="/facts/Conodont/wqA7V7cz">conodonts</a>, they are now supposed to have evolved independently of later vertebrates' teeth.
Living <a href="/facts/Amphibian/r2BleD2W">amphibians</a> typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there is some variation between species, most notably the venom-injecting <a href="/facts/Fang/IbsA3uNY">fangs</a> of <a href="/facts/Snake/YhA2gcn0">snakes</a>. The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their <a href="/facts/Mammal-like_reptiles/hXU6TAxB">evolutionary ancestors</a>. The numbers of these types of teeth vary greatly between species; <a href="/facts/Zoology/6Kj13mBt">zoologists</a> use a standardised <a href="/facts/Dental_formula/yMEdzfHh">dental formula</a> to describe the precise pattern in any given group.

Tooth open-in-new

Tooth