Dentition pertains to the development of teeth Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans. For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all and their arrangement in the mouth The mouth is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age.^[1] That is, the number, type, and morpho-physiology of the teeth of an animal.^[2]

Animals whose teeth are all of the same type, such as most non-mammalian vertebrates, are said to have homodont dentition, whereas those whose teeth differ morphologically are said to have heterodont The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida (which includes mammals) generally possess incisors, canines ('eyeteeth'), premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization in a species dentition. The dentition of animals with two successions of teeth ((deciduous Deciduous teeth, otherwise known as milk teeth, baby teeth, temporary teeth and primary teeth, are the first set of teeth in the growth development of humans and many other mammals. They develop during the embryonic stage of development and erupt—that is, they become visible in the mouth—during infancy. They are usually lost and replaced by, permanent) is referred to as diphyodont, while the dentition of animals with only one set of teeth throughout life is monophyodont. The dentition of animals in which the teeth are continuously discarded and replaced throughout life is termed polyphyodont.^[2]

Overview

Vertebrate dentition originated from a folding in of the placoderm's armour, evolving into the familiar condition of living reptiles Reptiles are animals in the class Reptilia characterized by breathing air, a "cold-blooded" (poikilothermic) metabolism, laying tough-shelled amniotic eggs (or retaining the same membrane system in species with live birth), and skin with scales or scutes. They are tetrapods (either having four limbs or being descended from four-limbed, amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species, and fish A fish is any aquatic vertebrate animal that is covered with scales, and equipped with two sets of paired fins and several unpaired fins. Most fish are "cold-blooded", or ectothermic, allowing their body temperatures to vary as ambient temperatures change. Fish are abundant in most bodies of water. They can be found in nearly all aquatic: a long row of pointed or sharp-sided, undifferentiated teeth (homodont) that are completely replaceable. The mammalian pattern is significantly different. The teeth in the upper and lower jaws in mammals have evolved a close-fitting relationship such that they operate together as a unit. "They occlude, that is, the chewing surfaces of the teeth are so constructed that the upper and lower teeth are able to fit precisely together, cutting, crushing, grinding or shearing the food caught between".^[3]

All mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not except the monotremes Monotremes are mammals that lay eggs (Prototheria) instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria), the xenarthrans, the pangolins A pangolin , also scaly anteater or tenggiling, is a mammal of the order Pholidota. There is only one extant family (Manidae) and one genus (Manis) of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with this adaptation. They are found in, and the cetaceans The order Cetacea (pronounced /sɨˈteɪʃə/, L. cetus, whale, from Greek) includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos),^{[citation needed]} have up to four distinct types of teeth, with a maximum number for each. These are the incisor Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below (cutting), the canine In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth. However, they can appear more flattened, causing them to resemble incisors and leading them to be called incisiform. They evolved and are used primarily for firmly holding food in order to tear it apart, and, the premolar The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or mastication. It has properties of both the anterior, and the molar Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone" (grinding). The incisors occupy the front of the tooth row in both upper and lower jaws. They are normally flat, chisel-shaped teeth that meet in an edge-to-edge bite. Their function is cutting, slicing, or gnawing food into manageable pieces that fit into the mouth for further chewing. The canines are immediately behind the incisors. In many mammals, the canines are pointed, tusk-shaped teeth, projecting beyond the level of the other teeth. In carnivores, they are primarily offensive weapons for bringing down prey. In other mammals such as some primates, they are used to split open hard surfaced food. The premolars and molars are at the back of the mouth. Depending on the particular mammal and its diet, these two kinds of teeth prepare pieces of food to be swallowed by grinding, shearing, or crushing. The specialised teeth - incisors, canines, premolars, and molars - are found in the same order in every mammal.^[4]

In many mammals the infants have a set of teeth that fall out and are replaced by adult teeth. These are called deciduous teeth, primary teeth, baby teeth or milk teeth.^[5][6] Animals that have two sets of teeth, one followed by the other, are said to be diphyodont. Normally the dental formula for milk teeth is the same as for adult teeth except that the molars are missing.

Dental formula

Because mammalian teeth are specialised for different functions, many mammal groups have lost teeth not needed in their adaptation. Tooth form has also undergone evolutionary modification as a result of natural selection for specialised feeding or other adaptations. Over time, different mammal groups have evolved distinct dental features, both in the number and type of teeth, and in the shape and size of the chewing surface.^[7]

The number of teeth of each type is written as a dental formula for one side of the mouth, or quadrant A circular sector or circle sector, is the portion of a circle enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. Its area can be calculated as described below, with the upper and lower teeth shown on separate rows. The number of teeth in a mouth is twice that listed as there are two sides. In each set, incisors (I) are indicated first, canines (C) second, premolars (P) third, and finally molars (M), giving I:C:P:M.^[7][8] So for example, the formula 2.1.2.3 for upper teeth indicates 2 incisors, 1 canine, 2 premolars, and 3 molars on one side of the upper mouth.

The deciduous dental formula is notated in lowercase lettering preceded by the letter d: e.g. di:dc:dm.^[8] An animal's dentition for either deciduous or permanent teeth can thus be expressed as a dental formula, written in the form of a fraction, which can be written as , or I.C.P.M / I.C.P.M.^[9][8] For example, the following formulae show the deciduous and permanent dentition of all catarrhine primates:

1. Deciduous: di² − dc¹ − dp² / di₂ − dc₁ − dp₂x2 = 20.^[5] This can also be written as . Or as , if the fact that it pertains to deciduous teeth is clearly stated, per examples found in some texts such as The Cambridge Dictionary of Human Biology and Evolution^[8]
2. Permanent: I² − C¹ − P² − M³ / I₂ − C₁ − P₂ − M₃ = 32.^[5] This can also be written as . When the upper and lower dental formulae are the same, some texts write the formula without a fraction (in this case, 2.1.2.3), on the implicit assumption that the reader will realise it must apply to both upper and lower quadrants. This is seen for example throughout The Cambridge Dictionary of Human Biology and Evolution.

The greatest number of teeth in any known placental Eutheria are a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals (such as humans) than to living marsupials (such as kangaroos). They are distinguished from non-eutherians by various features of the feet, ankles, jaws and teeth. One of the major differences between mammal was 48, with a formula of .^[7] However, no existing (or extant) placental mammal has this number. In extant placental mammals, the maximum dental formula is: Mammal teeth are usually symetrical, but not always. For example, the aye-aye The Aye-aye is a lemur, a strepsirrhine primate native to Madagascar that combines rodent-like teeth with a long, thin middle finger to fill the same ecological niche as a woodpecker. It is the world's largest nocturnal primate, and is characterized by its unusual method of finding food; it taps on trees to find grubs, then gnaws holes in the wood has a formula of , demonstrating the need for both upper and lower quadrant counts.^[8]

Tooth naming discrepancies

Teeth are numbered starting at 1 in each group, except the premolars which end at 4. Thus the human Humans are a species of animal known taxonomically as Homo sapiens , and are the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo teeth are I1, I2, C1, P3, P4, M1, M2, and M3.^[10] In humans, the third molar pertains to the wisdom tooth, whether or not it has erupted.^[11]

Regarding premolars, there is disagreement regarding whether the third type of dediduous tooth is a premolar (the general consensus among mammalogists) or a molar (commonly held among human anatomists).^[6] There is thus some discrepancy between nomenclature in zoology and in dentistry. This is because the terms of human dentistry, which have generally prevailed over time, have not included mammalian dental evolutionary theory. There were originally four premolars in each quadrant of early mammalian jaws. However, all living primates have lost at least the first premolar. "Hence most of the prosimians Prosimians are a grouping of mammals that are defined by being primates that are not monkeys or apes. They include, among others, lemurs, the Aye-aye, bushbabies, and tarsiers. They are considered to have characteristics that are more primitive than those of monkeys and apes. Prosimians are the only primates native to Madagascar, and are also and platyrrhines have three premolars. Some genera have also lost more than one. A second premolar has been lost in all catarrhines. The remaining permanent premolars are then properly identified as P2, P3 and P4 or P3 and P4; however, traditional dentistry refers to them as P1 and P2".^[5]

Dental eruption sequence

The order in which teeth emerge through the gums is known as the dental eruption sequence. Rapidly developing anthropoid primates such as macaques The macaques constitute a genus (Macaca, /məˈkäkə/) of Old World monkeys of the subfamily Cercopithecinae, chimpanzees Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:, and australopithecines The term australopithecine refers generally to any species in the related genera Australopithecus or Paranthropus. These species occurred in the Plio-Pleistocene era, and were bipedal and dentally similar to humans, but with a brain size not much larger than modern apes, lacking the encephalization characteristics of the genus Homo have an eruption sequence of M1 I1 I2 M2 P3 P4 C M3, whereas anatomically modern humans Anatomically modern human , Homo sapiens or early modern human in paleoanthropology refers to early individuals of Homo sapiens with an appearance similar to that of modern humans. Anatomically modern humans evolved from archaic Homo sapiens in the Middle Paleolithic, about 200,000 years ago. The emergence of anatomically modern human marks the have the sequence M1 I1 I2 C P3 P4 M2 M3. The later that tooth emergence begins, the earlier the anterior teeth (I1-P4) appear in the sequence.^[10]

Dental formulae examples

Dentition use in archaeology

Dentition, or the study of teeth, is an important area of study for archaeologists, especially those specializing in the study of older remains.^[27][28] Dentition affords many advantages over studying the rest of the skeleton itself (osteometry). The structure and arrangement of teeth is constant and, although it is inherited, does not undergo extensive change during environmental change, dietary specializations, or alterations in use patterns. The rest of the skeleton is much more likely to exhibit change because of adaptation. Teeth also preserve better than bone, and so the sample of teeth available to archaeologists is much more extensive and therefore more representative.

Dentition is particularly useful in tracking ancient populations' movements, because, although all humans have the same basic 32 teeth, there are subtle differences in the shapes of incisors, the number of grooves on molars, and extra cusps on particular teeth. These differences can not only be associated with different populations across space, but also change over time so that the study of the characteristics of teeth could say which population one is dealing with, and at what point in that population's history they are.

See also

• Odontometrics
• Phalangeal formula

Dentition discussions in other articles

Some articles have helpful discussions on dentition, which will be listed as identified.

• Lemur Lemurs (pronounced /ˈliːmə/, us dict: lē′·mər) are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures (ghosts or spirits) of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species. Although lemurs often are confused with ancestral

Further reading

• Daris R. Swindler (2002), "Chapter 1: Introduction (pp.1-11) and Chapter 2: Dental anatomy (pp.12-20).", Primate Dentition: An Introduction to the Teeth of Non-human Primates, Cambridge: Cambridge University Press, ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-521-65289-8, http://catdir.loc.gov/catdir/samples/cam031/2001037356.pdf See also preview pages in Google books

• Feldhamer, George A., Lee C. Drickhamer, Stephen H. Vessey, Joseph F. Merritt, Carey Krajewski (2007), "4: Evolution and Dental Characteristics", Mammalogy: Adaptation, Diversity, Ecology, Baltimore, Maryland: Johns Hopkins University Press The Johns Hopkins University Press is the publishing division of the Johns Hopkins University. It was founded in 1878 and holds the distinction of being the oldest continuously running university press in the United States. The Press publishes books, journals, and electronic databases. Considering all its units (books, journals, fulfillment, and, pp. 48-67, ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 978-0-8018-8695-9, http://books.google.com.au/books?id=udCnKce9hfoC&printsec=frontcover&dq=Mammalogy&hl=en&ei=x38NTKicEsuXcYO91JUO&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCsQ6AEwAA#v=onepage&q&f=false, retrieved 7 June 2010 (link provided to title page to give reader choice of scrolling straight to relevant chapter or perusing other material).

Notes

a. ^{^} Unless otherwise stated, the formulae can be assumed to be for adult, or permanent dentition.

b. ^{^} Regarding horse dentition, Pence gives erroneous upper and lower figures of 40 to 44 for the dental range.^[24] It is not possible to arrive at this range from the figures she provides. The figures from Cirelli^[25] and Ultimate Ungulates^[26] are more reliable, although there is a self-evident error for Cirelli's calculation of the upper female range of 40, which is not possible from the figures he provides. One can only arrive at an upper figure of 38 without canines, which for females Cirelli shows as 0/0. It appears canines do sometimes appear in females, hence the sentence in Ultimate Ungulates that canines are "usually present only in males",^[26] However, Pence's and Cirelli's references are clearly otherwise useful, hence the inclusion, but with the caveat of this footnote.

References

1. ^ Angus Stevenson, ed. (2007), "Dentition definition", Shorter Oxford English Dictionary The Shorter Oxford English Dictionary, often abbreviated to SOED, is a scaled-down version of the Oxford English Dictionary . It comprises two volumes rather than the twenty needed for the full second edition of the OED. The sixth edition was released in August 2007, 1: A-M (6th ed.), Oxford: Oxford University Press, p. 646, ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 978-0-19-920687-2
2. ^ ^{a b} E.A. Martin (1983), Macmillan Dictionary of Life Sciences (2nd revised ed.), London: Macmillan Press, p. 103, ISBN 0-333-38647-2
3. ^ Weiss, M.L., & Mann, A.E (1985), 'Human Biology and Behaviour: An anthropological perspective (4th ed.), Boston: Little Brown, pp. 130-131, ISBN 0-673-39013-6
4. ^ Weiss, M.L., & Mann, A.E (1985), p.132-135.
5. ^ ^{a b c d} Daris R. Swindler (2002), "Chapter 1: Introduction (pp.1-11) and Chapter 2: Dental anatomy (pp.12-20).", Primate Dentition: An Introduction to the Teeth of Non-human Primates, Cambridge: Cambridge University Press, p. 11, ISBN 0-521-65289-8, http://catdir.loc.gov/catdir/samples/cam031/2001037356.pdf
6. ^ ^{a b} Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), The Cambridge Dictionary of Human Biology and Evolution, Cambridge & New York: Cambridge University Press, p. 135, ISBN 978-0-521-66486-8
7. ^ ^{a b c} Weiss, M.L., & Mann, A.E (1985), p.134.
8. ^ ^{a b c d e f} Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.139
9. ^ ^{a b c d} E.A. Martin (1983), p.102
10. ^ ^{a b} Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.139. See section on dental eruption sequence, where numbering used is per this text.
11. ^ ^{a b c} Marvin Harris (1988), Culture, People, Nature: An Introduction to General Anthropology (5th ed.), New York: Harper & Row, ISBN 06-042697-7
12. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), pp.134,139.
13. ^ ^{a b} Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.177
14. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.550
15. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.340
16. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.335
17. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.267
18. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.438
19. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.309
20. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.371
21. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.300
22. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005), p.520
23. ^ Freeman, Patricia W., & Genoways, Hugh H (December 1998), "Recent Northern Records of the Nine-banded Armadillo (Dasypodidae) in Nebraska", The Southwestern Naturalist 43 (4): 491-504, http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1012&context=museummammalogy, retrieved 7 June 2010
24. ^ ^{a b c} Patricia Pence (2002), Equine Dentistry: A Practical Guide, Baltimore: Lippincott Williams & Wilkins, p. 7, ISBN 0-683-30403-8, http://books.google.com.au/books?id=o4KVGceXBNIC&printsec=frontcover&dq=%22Equine+dentistry%22&lr=lang_en&as_drrb_is=q&as_minm_is=0&as_miny_is=&as_maxm_is=0&as_maxy_is=&as_brr=3&cd=1#v=onepage&q&f=false
25. ^ ^{a b c d e} Al Cirelli, Equine Dentition, Nevada: University of Nevada, http://www.unce.unr.edu/publications/files/ag/2000/sp0008.pdf, retrieved 7 June 2010
26. ^ ^{a b c d} Family Equidae: Horses, asses, and zebras, Ulitimate Unqulate.com, http://www.ultimateungulate.com/Perissodactyla/Equidae.html, retrieved 7 June 2010
27. ^ Weiss, M.L., & Mann, A.E (1985), p.130-135.
28. ^ Larry L Mai; Marcus Young Owl; M Patricia Kersting (2005). The utility of dental formulae in species identification is indicated throughout this dictionary. Dental formulae are noted for many species, both extant and extinct, and where unknown (in some extinct species) this is noted.

Adovasio, J. M. and David Pedler. "The Peopling of North America." North American Archaeology. Blackwell Publishing, 2005. p. 35–36.

External links

• Colorado State's Dental Anatomy Page

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