Tooth

Edit links
Page semi-protected
Source: Wikipedia, the free encyclopedia.
This article is about the structure found in many animals. For the teeth of humans, see Human tooth. For other uses, see Tooth (disambiguation).

Tooth
A chimpanzee displaying his teeth
Details
Identifiers
Latindens
MeSHD014070
FMA12516
Anatomical terminology

A tooth (pl.: teeth) is a hard,

gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost 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

cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw.[1]

Monophyodonts are animals that develop only one set of teeth, while diphyodonts grow an early set of deciduous teeth and a later set of permanent or "adult" teeth. Polyphyodonts grow many sets of teeth. For example, sharks, 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.

Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Some rodents, such as voles and guinea pigs (but not mice), as well as lagomorpha (rabbits, hares and pikas), have continuously growing molars in addition to incisors.[2][3] Also, tusks (in tusked mammals) grow almost throughout life.[4]

Teeth are not always attached to the jaw, as they are in mammals. In many

dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of later vertebrates' teeth.[5][6]

Living

dental formula to describe the precise pattern in any given group.[1]

Etymology

The word tooth comes from

Proto-Indo-European *h₁dent-, which was composed of the root *h₁ed- 'to eat' plus the active participle suffix *-nt, therefore literally meaning 'that which eats'.[7]

The irregular plural form teeth is the result of Germanic umlaut whereby vowels immediately preceding a high vocalic in the following syllable were raised. As the nominative plural ending of the Proto-Germanic consonant stems (to which *tanþs belonged) was *-iz, the root vowel in the plural form *tanþiz (changed by this point to *tą̄þi via unrelated phonological processes) was raised to /œː/, and later unrounded to /eː/, resulting in the tōþ/tēþ alternation attested from Old English. Cf. also Old English bōc/bēċ 'book/books' and 'mūs/mȳs' 'mouse/mice', from Proto-Germanic *bōks/bōkiz and *mūs/mūsiz respectively.

Cognate with Latin dēns, Greek ὀδούς (odous), and Sanskrit dát.

Origin

Teeth are assumed to have evolved either from

jawless vertebrates) (the "inside–out" theory). In addition, there is another theory stating that neural crest gene regulatory network, and neural crest-derived ectomesenchyme are the key to generate teeth (with any epithelium, either ectoderm or endoderm).[4][8]

The genes governing tooth development in mammals are

Romundina stellina showed that the teeth and scales were made of the same tissues, also found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales.[10]

Mammals

Main article: Mammal tooth

Teeth are among the most distinctive (and long-lasting) features of

canine teeth
to kill prey and to tear meat.

Mammals, in general, are

manatees are unusual among mammals because they are polyphyodonts
.

Aardvark

In

Tubulidentata.[11]

Canines

Main article: Canine tooth

In

dental cavities because of the very high pH of dog saliva, which prevents enamel from demineralizing.[12] Sometimes called cuspids, these teeth are shaped like points (cusps) and are used for tearing and grasping food.[13]

Cetaceans

Main article: Baleen

Like human teeth, whale teeth have polyp-like protrusions located on the root surface of the tooth. These polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber. While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a very small layer of enamel at the tip. This small enamel layer is only seen in older whales where the cementum has been worn away to show the underlying enamel.[14]

The toothed whale is a

Beaked whales
are almost toothless, with only bizarre teeth found in males. These teeth may be used for feeding but also for demonstrating aggression and showmanship.

Primates

Main articles: Human tooth and Dental anatomy

In

wisdom teeth, although these are not present in all adults, and may be removed surgically later in life.[15]

Among primary teeth, 10 of them are usually found in the

mandible
(i.e. lower jaw). Among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. Most of the teeth have uniquely distinguishing features.

Horse

Main article: Horse teeth

An adult

vestigial premolars, with most of those having only one or two. They are equally common in male and female horses and much more likely to be on the upper jaw. If present these can cause problems as they can interfere with the horse's bit contact. Therefore, wolf teeth are commonly removed.[17]

Horse teeth can be used to estimate the animal's age. Between birth and five years, age can be closely estimated by observing the eruption pattern on milk teeth and then permanent teeth. By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth. After the age of five, age can only be conjectured by studying the wear patterns on the incisors, shape, the angle at which the incisors meet, and other factors. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing. Two horses of the same age may have different wear patterns.

A horse's incisors, premolars, and molars, once fully developed, continue to erupt as the grinding surface is worn down through chewing. A young adult horse will have teeth, which are 110–130 mm (4.5–5 inches) long, with the majority of the crown remaining below the gumline in the dental socket. The rest of the tooth will slowly emerge from the jaw, erupting about 3 mm (1⁄8 in) each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars, may need to have their fodder ground up and soaked in water to create a soft mush for them to eat in order to obtain adequate nutrition.

Proboscideans

Elephant ivory

Elephants' tusks are specialized incisors for digging food up and fighting. Some elephant teeth are similar to those in manatees, and elephants are believed to have undergone an aquatic phase in their evolution.

At birth, elephants have a total of 28 molar plate-like grinding teeth not including the tusks. These are organized into four sets of seven successively larger teeth which the elephant will slowly wear through during its lifetime of chewing rough plant material. Only four teeth are used for chewing at a given time, and as each tooth wears out, another tooth moves forward to take its place in a process similar to a conveyor belt. The last and largest of these teeth usually becomes exposed when the animal is around 40 years of age, and will often last for an additional 20 years. When the last of these teeth has fallen out, regardless of the elephant's age, the animal will no longer be able to chew food and will die of starvation.[19][20]

Rabbit

lagomorphs usually shed their deciduous teeth before (or very shortly after) their birth, and are usually born with their permanent teeth.[21] The teeth of rabbits complement their diet, which consists of a wide range of vegetation. Since many of the foods are abrasive enough to cause attrition, rabbit teeth grow continuously throughout life.[22] Rabbits have a total of six incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. There are no canines. Dental formula is 2.0.3.31.0.2.3 = 28. Three to four millimeters of the tooth is worn away by incisors every week, whereas the cheek teeth require a month to wear away the same amount.[23]

The incisors and cheek teeth of rabbits are called aradicular hypsodont teeth. This is sometimes referred to as an elodent dentition. These teeth grow or erupt continuously. The growth or eruption is held in balance by dental abrasion from chewing a diet high in fiber.

Buccal view of top incisor from Rattus rattus. Top incisor outlined in yellow. Molars circled in blue.
Buccal view of the lower incisor from the right dentary of a Rattus rattus
Lingual view of the lower incisor from the right dentary of a Rattus rattus
Midsagittal view of top incisor from Rattus rattus. Top incisor outlined in yellow. Molars circled in blue.

Rodents

guinea pigs.[28][29]

Lingual view of top incisor from Rattus rattus. Top incisor outlined in yellow. Molars circled in blue.

The teeth have enamel on the outside and exposed dentin on the inside, so they

diastema
region.

Manatee

Manatees are polyphyodont with mandibular molars developing separately from the jaw and are encased in a bony shell separated by soft tissue.[30][31]

Walrus

Main article: Walrus ivory

Walrus tusks are canine teeth that grow continuously throughout life.[32]

Fish

Teeth of a great white shark
See also: Pharyngeal teeth and Shark tooth

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.

Unlike the continuous shedding of functional teeth seen in modern sharks,

stem chondrichthyan lineages retained all tooth generations developed throughout the life of the animal.[35] This replacement mechanism is exemplified by the tooth whorl-based dentitions of acanthodians,[36] which include the oldest known toothed vertebrate, Qianodus duplicis[37]
.

Amphibians

All amphibians have pedicellate teeth, which are modified to be flexible due to connective tissue and uncalcified dentine that separates the crown from the base of the tooth.[38]

Most amphibians exhibit teeth that have a slight attachment to the jaw or

bicuspid shaped teeth.[40]

Reptiles

The teeth of

Crocodilian juveniles replace teeth with larger ones at a rate as high as one new tooth per socket every month. Once mature, tooth replacement rates can slow to two years and even longer. Overall, crocodilians may use 3,000 teeth from birth to death. New teeth are created within old teeth.[41]

Birds

Main article: Ichthyornis

A skull of Ichthyornis discovered in 2014 suggests that the beak of birds may have evolved from teeth to allow chicks to escape their shells earlier, and thus avoid predators and also to penetrate protective covers such as hard earth to access underlying food.[42][43]

Invertebrates

European medicinal leech
has three jaws with numerous sharp teeth which function like little saws for incising a host.

True teeth are unique to vertebrates,

analogous structures often referred to as teeth. The organisms with the simplest genome bearing such tooth-like structures are perhaps the parasitic worms of the family Ancylostomatidae.[45] For example, the hookworm Necator americanus has two dorsal and two ventral cutting plates or teeth around the anterior margin of the buccal capsule. It also has a pair of subdorsal and a pair of subventral teeth located close to the rear.[46]

Historically, the

anaesthetics, they suck out blood, consuming up to ten times their body weight in a single meal.[48]

In some species of Bryozoa, the first part of the stomach forms a muscular gizzard lined with chitinous teeth that crush armoured prey such as diatoms. Wave-like peristaltic contractions then move the food through the stomach for digestion.[49]

tensile strength
of any biological material.

Molluscs have a structure called a radula, which bears a ribbon of chitinous teeth. However, these teeth are histologically and developmentally different from vertebrate teeth and are unlikely to be homologous. For example, vertebrate teeth develop from a neural crest mesenchyme-derived dental papilla, and the neural crest is specific to vertebrates, as are tissues such as enamel.[44]

The radula is used by molluscs for feeding and is sometimes compared rather inaccurately to a

oesophagus. The radula is unique to molluscs, and is found in every class of mollusc apart from bivalves
.

Within the

gastropods, the radula is used in feeding by both herbivorous and carnivorous snails and slugs
. The arrangement of teeth (also known as denticles) on the radula ribbon varies considerably from one group to another as shown in the diagram on the left.

Predatory marine snails such as the

earthworms. Predatory cephalopods, such as squid
, use the radula for cutting prey.

In most of the more ancient lineages of gastropods, the radula is used to graze by scraping

human teeth.[51]

Fossilization and taphonomy

Because teeth are very resistant, often preserved when bones are not,

thelodonts had scales composed of dentine and an enamel-like compound, suggesting that the origin of teeth was from scales which were retained in the mouth. Fish as early as the late Cambrian had dentine in their exoskeletons, which may have functioned in defense or for sensing their environments.[54] Dentine can be as hard as the rest of teeth and is composed of collagen fibres, reinforced with hydroxyapatite.[54]

Though teeth are very resistant, they also can be brittle and highly susceptible to cracking.[55] However, cracking of the tooth can be used as a diagnostic tool for predicting bite force. Additionally, enamel fractures can also give valuable insight into the diet and behaviour of archaeological and fossil samples.

Decalcification removes the enamel from teeth and leaves only the organic interior intact, which comprises dentine and cementine.[56] Enamel is quickly decalcified in acids,[57] perhaps by dissolution by plant acids or via diagenetic solutions, or in the stomachs of vertebrate predators.[56] Enamel can be lost by abrasion or spalling,[56] and is lost before dentine or bone are destroyed by the fossilisation process.[57] In such a case, the 'skeleton' of the teeth would consist of the dentine, with a hollow pulp cavity.[56] The organic part of dentine, conversely, is destroyed by alkalis.[57]

See also

References

  1. ^
    ISBN 978-0-03-910284-5
    .
  2. PMID 12571097
    .
  3. S2CID 45097018
    .
  4. ^
    S2CID 220585014
    .
  5. PMID 11523817
    .
  6. ^ nature.com, Fossil scans reveal origins of teeth, 16 October 2013
  7. ^ Harper, Douglas (2001–2021). "tooth | Origin and meaning of tooth". Online Etymology Dictionary.
  8. PMID 24009032
    .
  9. S2CID 18868124
    .
  10. ^ Jennifer Viegas (June 24, 2015). "First-known teeth belonged to fierce fish". ABC Science. Retrieved June 28, 2015.
  11. ^ Shoshani 2002, p. 619
  12. PMID 20190984
    .
  13. ^ "Types of Teeth, Dental Anatomy & Tooth Anatomy | Colgate®". www.colgate.com. Archived from the original on 2017-11-19. Retrieved 2017-11-19.
  14. ^ "Common Characteristics Of Whale Teeth". Archived from the original on 4 September 2011. Retrieved 18 July 2014.
  15. ^ "Everything you need to know about teeth". NHS Scotland. Retrieved 5 May 2020.
  16. ^ "Gummed Out: Young Horses Lose Many Teeth, Vet Says". Archived from the original on 8 July 2014. Retrieved 6 July 2014.
  17. ^
    ISBN 978-0-683-30403-9
    .
  18. ^ Al Cirelli. "Equine Dentition" (PDF). University of Nevada Reno. SP-00-08. Retrieved 7 June 2010.
  19. ISBN 978-0-7614-7266-7
    .
  20. ISBN 0-8343-0051-6
  21. ^ Dental Anatomy & Care for Rabbits and Rodents
  22. ^ Brown, Susan. Rabbit Dental Diseases Archived 2007-10-14 at the Wayback Machine, hosted on the San Diego Chapter of the House Rabbit Society Archived 2007-10-13 at the Wayback Machine. Page accessed April 9, 2007.
  23. ^ Ryšavy, Robin. Hay & Dental Health, hosted by the Missouri House Rabbit Society-Kansas City. Page accessed January 2, 2024.
  24. ^
    ISBN 9781107044333
    .
  25. ^ Caceci, Thomas. Veterinary Histology with subtitle "Digestive System: Oral Cavity" found here Archived 2006-04-30 at the Wayback Machine.
  26. S2CID 13197331
    .
  27. doi:10.1080/02724634.1999.10011164
    .
  28. ^ a b Tummers M and Thesleff I. Root or crown: a developmental choice orchestrated by the differential regulation of the epithelial stem cell niche in the tooth of two rodent species. Development (2003). 130(6):1049-57.
  29. ^ a b AM Hunt. A description of the molar teeth and investing tissues of normal guinea pigs. J Dent Res. (1959) 38(2):216-31.
  30. ISBN 0-87596-143-6
    .
  31. ISBN 0-87196-871-1
    .
  32. ^ The Permanent Canine Teeth, hosted on the University of Illinois at Chicago website. Page accessed February 5, 2007.
  33. S2CID 12821592
    .
  34. S2CID 92225621
    , retrieved 2022-10-22
  35. S2CID 233985000
    .
  36. OCLC 1335983356
    .
  37. S2CID 252569771
    .
  38. ^ Pough, Harvey. Vertebrate Life. 9th Ed. Boston: Pearson Education, Inc., 2013. 211-252. Print.
  39. ISBN 9780078023026
    .
  40. ^ Xiong, Jianli (2014). "Comparison of vomerine tooth rows in juvenile and adult Hynobius guabangshanensis". Vertebrate Zoology. 64: 215–220.
  41. doi:10.1111/j.1469-7998.1961.tb06083.x
    .
  42. ^ Hersher, Rebecca (May 2, 2018). "How Did Birds Lose Their Teeth And Get Their Beaks? Study Offers Clues". NPR.
  43. ^ Field, Daniel J.; Hanson, Michael; Burnham, David; Wilson, Laura E.; Super, Kristopher; Ehret, Dana; Ebersole, Jun A.; Bhullar, Bhart-Anjan S. (May 31, 2018). "Complete Ichthyornis skull illuminates mosaic assembly of the avian head". Nature Vol 557, pp 96 - 100.
  44. ^
    ISBN 978-0-697-21991-6
    .
  45. ^ "Ancylostoma duodenale". Nematode.net Genome Sequencing Center. Archived from the original on 2008-05-16. Retrieved 2009-10-27.
  46. ^ Roberts, Larry S., and John Janovy, Jr. Foundations of Parasitology. Seventh ed. Singapore: McGraw-Hill, 2006.
  47. ISBN 978-0-87969-146-2
    .
  48. S2CID 27891377
    .
  49. ISBN 978-0-03-025982-1
    .
  50. ^
    PMID 25694539
  51. ^ Zachary Davies Boren (18 February 2015). "The strongest materials in the world: Limpet teeth beats record resistance of spider silk". The Independent. Retrieved 20 February 2015.
  52. ISBN 978-0-521-59833-0
  53. S2CID 24296825
    . Retrieved 2019-01-09.
  54. ^
    ISBN 978-0-521-03372-5
    , Chapter 5.
  55. S2CID 205599560
    .
  56. ^
    hdl:2027.42/48503
    .
  57. ^
    doi:10.1111/1475-4754.t01-1-00068
    .
Wikimedia Commons has media related to tooth.

Sources

  • Shoshani, Jeheskel (2002). "Tubulidentata". In Robertson, Sarah (ed.). Encyclopedia of Life Sciences. Vol. 18: Svedberg, Theodor to Two-hybrid and Related Systems. London, UK: Nature Publishing Group.
    ISBN 978-1-56159-274-6
    .

External links
Look up tooth in Wiktionary, the free dictionary.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Tooth&oldid=1213684979"
This page is based on the copyrighted Wikipedia article: Tooth . Articles is available under the CC BY-SA 3.0 license; additional terms may apply.Privacy Policy