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Cast of a human upper jaw showing incisors, canines, premolars, and two of the three possible sets of molars.

Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, type, and number of teeth in a given species at a given age,[1] as well as the morpho-physiology (that is, the relationship between the shape and form of the tooth in question and its inferred function) of the animal's teeth.[2]

Terminology

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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 dentition. The dentition of animals with two successions of teeth (deciduous, 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] The dentition of animals in which the teeth are set in sockets in the jawbones is termed thecodont.

Overview

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The evolutionary origin of the vertebrate dentition remains contentious. Current theories suggest either an "outside-in" or "inside-out" evolutionary origin to teeth, with the dentition arising from odontodes on the skin surface moving into the mouth, or vice versa.[3] Despite this debate, it is accepted that vertebrate teeth are homologous to the dermal denticles found on the skin of basal Gnathostomes (i.e. Chondrichtyans).[4] Since the origin of teeth some 450 mya, the vertebrate dentition has diversified within the reptiles, amphibians, and fish: however most of these groups continue to possess 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 tearing the food caught between."[5]

Mammals have up to four distinct types of teeth, though not all types are present in all mammals. These are the incisor (cutting), the canine, the premolar, and the molar (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. In humans, the canine teeth are the main components in occlusal function and articulation.

The mandibular teeth function against the maxillary teeth in a particular movement that is harmonious to the shape of the occluding surfaces. This creates the incising and grinding functions. The teeth must mesh together the way gears mesh in a transmission. If the interdigitation of the opposing cusps and incisal edges are not directed properly the teeth will wear abnormally (attrition), break away irregular crystalline enamel structures from the surface (abrasion), or fracture larger pieces (abfraction). This is a three-dimensional movement of the mandible in relation to the maxilla.

There are three points of guidance for movement of the teeth: the two posterior points provided by the temporomandibular joints and the anterior component provided by the incisors and canines. The incisors mostly control the vertical opening of the chewing cycle when the muscles of mastication move the jaw forwards and backwards (protrusion/retrusion). The canines come into function guiding the vertical movement when the chewing is side to side (lateral). The canines alone can cause the other teeth to separate at the extreme end of the cycle (cuspid guided function) or all the posterior teeth can continue to stay in contact (group function). The entire range of this movement is the envelope of masticatory function. The initial movement inside this envelope is directed by the shape of the teeth in contact and the Glenoid Fossa/Condyle shape. The outer extremities of this envelope are limited by muscles, ligaments and the articular disc of the TMJ. Without the guidance of anterior incisors and canines, this envelope of function can be destructive to the remaining teeth resulting in periodontal trauma from occlusion seen as wear, fracture or tooth loosening and loss.

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.[6] 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.[7][8] 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.[9]

Dental formula

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Because every mammal's teeth are specialised for different functions, many mammal groups have lost the teeth that are 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.[10]

The number of teeth of each type is written as a dental formula for one side of the mouth, or quadrant, 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.[10][11] 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: for example: di:dc:dp.[11]

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 I.C.P.MI.C.P.M, or I.C.P.M / I.C.P.M.[11][12] For example, the following formulae show the deciduous and usual permanent dentition of all catarrhine primates, including humans:

  1. Deciduous: [7] This can also be written as di2.dc1.dm2di2.dc1.dm2. Superscript and subscript denote upper and lower jaw, i.e. do not indicate mathematical operations; the numbers are the count of the teeth of each type. The dashes (-) in the formula are likewise not mathematical operators, but spacers, meaning "to": for instance the human formula is 2.1.2.2-32.1.2.2-3 meaning that people may have 2 or 3 molars on each side of each jaw. 'd' denotes deciduous teeth (i.e. milk or baby teeth); lower case also indicates temporary teeth. Another annotation is 2.1.0.22.1.0.2, 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.[11]
  2. Permanent: [7] This can also be written as 2.1.2.32.1.2.3. 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 land mammal[specify] was 48, with a formula of 3.1.5.33.1.5.3.[10] However, no living placental mammal has this number. In extant placental mammals, the maximum dental formula is 3.1.4.33.1.4.3 for pigs. Mammalian tooth counts are usually identical in the upper and lower jaws, but not always. For example, the aye-aye has a formula of 1.0.1.31.0.0.3, demonstrating the need for both upper and lower quadrant counts.[11]

Tooth naming discrepancies

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Teeth are numbered starting at 1 in each group. Thus the human teeth are I1, I2, C1, P3, P4, M1, M2, and M3.[13] (See next paragraph for premolar naming etymology.) In humans, the third molar is known as the wisdom tooth, whether or not it has erupted.[14]

Regarding premolars, there is disagreement regarding whether the third type of deciduous tooth is a premolar (the general consensus among mammalogists) or a molar (commonly held among human anatomists).[8] 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 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".[7]

Dental eruption sequence

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The order in which teeth emerge through the gums is known as the dental eruption sequence. Rapidly developing anthropoid primates such as macaques, chimpanzees, and australopithecines have an eruption sequence of M1 I1 I2 M2 P3 P4 C M3, whereas anatomically modern humans 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.[13]

Dental formulae examples

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Some examples of mammalian dental formulae[15]
Species Dental formula Comment
Non placental Non-placental mammals such as marsupials (e.g., opossums) can have more teeth than placentals.
Bilby 5.1.3.43.1.3.4[16]
Kangaroo 3.1.2.41.0.2.4[17]
Musky rat-kangaroo 3.1.1.42.0.1.4[18]
Rest of Potoroidae 3.1.1.41.0.1.4[18] The marsupial family Potoroidae includes the bettongs, potoroos, and two of the rat-kangaroos. All are rabbit-sized, brown, jumping marsupials and resemble a large rodent or a very small wallaby.
Tasmanian devil 4.1.2.43.1.2.4 [19]
Opossum 5.1.3.44.1.3.4 [20]
Placental Some examples of dental formulae for placental mammals.
Apes 2.1.2.32.1.2.3 All apes (excluding 20–23% of humans) and Old World monkeys share this formula, sometimes known as the cercopithecoid dental formula.[14]
Armadillo 0.0.7.10.0.7.1[21]
Aye-aye 1.0.1.31.0.0.3[22] A prosimian. The aye-aye's deciduous dental formula (dI:dC:dM) is 2.1.22.1.2.[11]
Badger 3.1.3.13.1.3.2[23]
Big brown bat 2.1.1.33.1.2.3[20]
Red bat, hoary bat, Seminole bat, Mexican free-tailed bat 1.1.2.33.1.2.3[20]
Camel 1.1.3.33.1.2.3[24]
Cat (deciduous) 3.1.3.03.1.2.0[25]
Cat (permanent) 3.1.3.13.1.2.1[12] The last upper premolar and first lower molar of the cat, since it is a carnivore, are called carnassials and are used to slice meat and skin.
Cow 0.0.3.33.1.3.3[26] The cow has no upper incisors or canines, the rostral portion of the upper jaw forming a dental pad. The lower canine is incisiform, giving the appearance of a 4th incisor.
Dog (deciduous) 3.1.3.03.1.3.0[25]
Dog (permanent) 3.1.4.23.1.4.3[23]
Eared Seal 3.1.4.1-32.1.4.1[27]
Eulemur 3.1.3.33.1.3.3 Prosimian genus to which the large Malagasy or 'true' lemurs belong.[28] Ruffed lemurs (genus Varecia),[29] dwarf lemurs (genus Mirza),[30] and mouse lemurs (genus Microcebus) also have this dental formula, but the mouse lemurs have a dental comb.[31]
Euoticus 2.1.3.32.1.3.3 Prosimian genus to which the needle-clawed bushbabies (or galagos) belong. Specialised morphology for gummivory includes procumbent dental comb and caniniform upper anterior premolars.[28]
Fox (red) 3.1.4.23.1.4.3[23]
Guinea pig 1.0.1.31.0.1.3[32]
Hedgehog 3.1.3.32.1.2.3[23]
Horse (deciduous) 3.0.3.03.0.3.0[33][34]
Horse (permanent) 3.0-1.3-4.33.0-1.3.3 Permanent dentition varies from 36 to 42, depending on the presence or absence of canines and the number of premolars.[35] The first premolar (wolf tooth) may be absent or rudimentary,[33][34] and is mostly present only in the upper (maxillary) jaw.[34] The canines are small and spade-shaped, and usually present only in males.[35] Canines appear in 20–25% of females and are usually smaller than in males.[34][36]
Human (deciduous teeth) See comment Either 2.1.2.02.1.2.0 or 2.1.0.22.1.0.2. Human anatomists and mammal anatomists differ on whether the two anterior deciduous teeth are premolars (mammalogists) or molars (human anatomists)
Human (permanent teeth) 2.1.2.2-32.1.2.2-3 Wisdom teeth are congenitally absent in 20–23% of the human population; the proportion of agenesis of wisdom teeth varies considerably among human populations, ranging from a near 0% incidence rate among Aboriginal Tasmanians to near 100% among Indigenous Mexicans.[37]
Indri See comment A prosimian. Dental formula disputed. Either 2.1.2.32.0.2.3 or 2.1.2.31.1.2.3. Proponents of both formulae agree there are 30 teeth and that there are only four teeth in the dental comb.[38]
Lepilemur 0.1.3.32.1.3.3 A prosimian. The upper incisors are lost in the adult, but are present in the deciduous dentition.[39]
Lion 3.1.3.13.1.2.1[40]
Mole 3.1.4.33.1.4.3[23]
Mouse 1.0.0.31.0.0.3[23] Plains pocket mouse (Perognathus flavescens) have dental formula of 1.0.1.31.0.1.3.[41]
New World monkeys See comment All New World monkeys have a dentition formula of 2.1.3.32.1.3.3 or 2.1.3.22.1.3.2.[14]
Pantodonta 3.1.4.33.1.4.3[42] Extinct suborder of early eutherians.
Pig (deciduous) 3.1.4.03.1.4.0[25]
Pig (permanent) 3.1.4.33.1.4.3[23]
Rabbit 2.0.3.31.0.2.3[12]
Raccoon 3.1.4.23.1.4.2
Rat 1.0.0.31.0.0.3[23]
Sheep (deciduous) 0.0.3.04.0.3.0[25]
Sheep (permanent) 0.0.3.33.1.3.3[20]
Shrew 3.1.3.33.1.3.3[23]
Sifakas See comment Prosimians. Dental formula disputed. Either 2.1.2.32.0.2.3 or 2.1.2.31.1.2.3. Possess dental comb comprising four teeth.[43]
Slender loris
Slow loris		 2.1.3.32.1.3.3 Prosimians. Lower incisors and canines form a dental comb; upper anterior dentition is peg-like and short.[44][45]
Squirrel 1.0.2.31.0.1.3[23]
Tarsiers 2.1.3.31.1.3.3 Prosimians.[46]
Tiger 3.1.3.13.1.2.1[47]
Vole (field) 1.0.0.31.0.0.3[23]
Weasel 3.1.3.13.1.3.2[23]

Dentition use in archaeology

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Dentition, or the study of teeth, is an important area of study for archaeologists, especially those specializing in the study of older remains.[48][49][50] 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 there are differences in the shapes of incisors, the number of grooves on molars, presence/absence of wisdom teeth, 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.

Dinosaurs

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A dinosaur's dentition included all the teeth in its jawbones, which consist of the dentary, maxillary, and in some cases the premaxillary bones. The maxilla is the main bone of the upper jaw. The premaxilla is a smaller bone forming the anterior of the animal's upper jaw. The dentary is the main bone that forms the lower jaw (mandible). The predentary is a smaller bone that forms the anterior end of the lower jaw in ornithischian dinosaurs; it is always edentulous and supported a horny beak.

Unlike modern lizards, dinosaur teeth grew individually in the sockets of the jawbones, which are known as the dental alveoli. This thecodont dentition is also present in crocodilians and mammals, but is not found among the non-archosaur reptiles, which instead have acrodont or pleurodont dentition.[51] Teeth that were lost were replaced by teeth below the roots in each tooth socket. Occlusion refers to the closing of the dinosaur's mouth, where the teeth from the upper and lower parts of the jaw meet. If the occlusion causes teeth from the maxillary or premaxillary bones to cover the teeth of the dentary and predentary, the dinosaur is said to have an overbite, the most common condition in this group. The opposite condition is considered to be an underbite, which is rare in theropod dinosaurs.

The majority of dinosaurs had teeth that were similarly shaped throughout their jaws but varied in size. Dinosaur tooth shapes included cylindrical, peg-like, teardrop-shaped, leaf-like, diamond-shaped and blade-like. A dinosaur that has a variety of tooth shapes is said to have heterodont dentition. An example of this are dinosaurs of the group Heterodontosauridae and the enigmatic early dinosaur, Eoraptor. While most dinosaurs had a single row of teeth on each side of their jaws, others had dental batteries where teeth in the cheek region were fused together to form compound teeth. Individually these teeth were not suitable for grinding food, but when joined together with other teeth they would form a large surface area for the mechanical digestion of tough plant materials. This type of dental strategy is observed in ornithopod and ceratopsian dinosaurs as well as the duck-billed hadrosaurs, which had more than one hundred teeth in each dental battery. The teeth of carnivorous dinosaurs, called ziphodont, were typically blade-like or cone-shaped, curved, with serrated edges. This dentition was adapted for grasping and cutting through flesh. In some cases, as observed in the railroad-spike-sized teeth of Tyrannosaurus rex, the teeth were designed to puncture and crush bone. Some dinosaurs had procumbent teeth, which projected forward in the mouth.[52]

See also

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

Citations

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  1. ^ Angus Stevenson, ed. (2007), "Dentition definition", Shorter Oxford English Dictionary, vol. 1: A–M (6th ed.), Oxford: Oxford University Press, p. 646, ISBN 978-0-19-920687-2
  2. ^ a b Martin (1983), p. 103
  3. ^ Fraser, G. J.; et al. (2010). "The odontode explosion: The origin of tooth-like structures in vertebrates". BioEssays. 32 (9): 808–817. doi:10.1002/bies.200900151. PMC 3034446. PMID 20730948.
  4. ^ Martin et al. (2016) Sox2+ progenitors in sharks link taste development with the evolution of regenerative teeth from denticles, PNAS
  5. ^ Weiss & Mann (1985), pp. 130–131
  6. ^ Weiss & Mann (1985), pp. 132–135
  7. ^ a b c d Swindler (2002), p. 11
  8. ^ a b Mai, Young Owl & Kersting (2005), p. 135
  9. ^ "What Is a Diphyodont?". Worldatlas. November 30, 2018.
  10. ^ a b c Weiss & Mann (1985), p. 134
  11. ^ a b c d e f Mai, Young Owl & Kersting (2005), p. 139
  12. ^ a b c Martin (1983), p. 102
  13. ^ a b Mai, Young Owl & Kersting (2005), p. 139. See section on dental eruption sequence, where numbering used is per this text.
  14. ^ a b c Marvin Harris (1988), Culture, People, Nature: An Introduction to General Anthropology (5th ed.), New York: Harper & Row, ISBN 978-0-06-042697-2
  15. ^ Unless otherwise stated, the formulae can be assumed to be for adult, or permanent dentition.
  16. ^ Johnson, Ken A. (n.d.). ""Fauna of Australia"" (PDF). Fauna of Australia Volume 1b - Mammalia. Retrieved 2021-05-15. Fauna of Australia Volume 1b - Mammalia
  17. ^ "Kangaroo". www.1902encyclopedia.com. Archived from the original on 4 July 2017. Retrieved 28 March 2018.
  18. ^ a b Andrew W. Claridge; John H. Seebeck; Randy Rose (2007), Bettongs, Potoroos and the Musky Rat-kangaroo, Csiro Publishing, ISBN 978-0-643-09341-6
  19. ^ University Of Edinburgh Natural History Collection, archived from the original on 2012-03-01
  20. ^ a b c d Dental formulae of mammal skulls of North America, Wildwood Tracking, archived from the original on 2011-04-14
  21. ^ 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, JSTOR 30054089, archived from the original on 2011-06-11
  22. ^ Mai, Young Owl & Kersting (2005), pp. 134, 139
  23. ^ a b c d e f g h i j k l "The Skulls". Chunnie's British Mammal Skulls. Archived from the original on 8 October 2012. Retrieved 15 October 2011.
  24. ^ Bravo, P. Walter (2016-08-27). "Camelidae". veteriankey.com. Retrieved 2021-05-15. The dental formula for both Bactrian and dromedary camels is incisors (I) 1/3, canines (C) 1/1, premolars (P) 3/2, molars (M) 3/3.
  25. ^ a b c d "Dental formulae". www.provet.co.uk. Retrieved 28 March 2018.
  26. ^ "Using Dentition to Age Cattle". fsis.usda.gov. Archived from the original on 2008-09-16. Retrieved 2008-09-06.
  27. ^ Myers, Phil (2000). ""Otariidae"". Animal Diversity Web. Retrieved 2021-05-15. The dental formula is 3/2, 1/1, 4/4, 1-3/1 = 34-38.
  28. ^ a b Mai, Young Owl & Kersting (2005), p. 177
  29. ^ Mai, Young Owl & Kersting (2005), p. 550
  30. ^ Mai, Young Owl & Kersting (2005), p. 340
  31. ^ Mai, Young Owl & Kersting (2005), p. 335
  32. ^ Noonan, Denise. "The Guinea Pig (Cavia porcellus)" (PDF). ANZCCART. Archived (PDF) from the original on 2016-08-04.
  33. ^ a b Pence (2002), p. 7
  34. ^ a b c d Cirelli
  35. ^ a b Ultimate Ungulates
  36. ^ Regarding horse dentition, Pence (2002, p. 7) gives erroneous upper and lower figures of 40 to 44 for the dental range. It is not possible to arrive at this range from the figures she provides. The figures from Cirelli and Ultimate Ungulates 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". However, Pence's and Cirelli's references are clearly otherwise useful, hence the inclusion, but with the caveat of this footnote.
  37. ^ Rozkovcová, E.; Marková, M.; Dolejší, J. (1999). "Studies on agenesis of third molars amongst populations of different origin". Sborník Lékařský. 100 (2): 71–84. PMID 11220165.
  38. ^ Mai, Young Owl & Kersting (2005), p. 267
  39. ^ Mai, Young Owl & Kersting (2005), p. 300
  40. ^ "Dental Formula". www.geocities.ws. Archived from the original on 28 February 2017. Retrieved 28 March 2018.
  41. ^ "Plains Pocket Mouse (Perognathus flavescens)". www.nsrl.ttu.edu. Archived from the original on 7 October 2017. Retrieved 28 March 2018.
  42. ^ Rose, Kenneth David (2006). "Cimolesta". The Beginning of the Age of Mammals. Johns Hopkins University Press. pp. 94–118. ISBN 978-0-8018-8472-6.
  43. ^ Mai, Young Owl & Kersting (2005), p. 438
  44. ^ Mai, Young Owl & Kersting (2005), p. 309
  45. ^ Mai, Young Owl & Kersting (2005), p. 371
  46. ^ Mai, Young Owl & Kersting (2005), p. 520
  47. ^ Emily, Peter P.; Eisner, Edward R. (2021-06-16). Zoo and Wild Animal Dentistry. Wiley-Blackwell. p. 319. ISBN 978-1119545811.
  48. ^ Towle, Ian; Irish, Joel D.; Groote, Isabelle De (2017). "Behavioral inferences from the high levels of dental chipping in Homo naledi" (PDF). American Journal of Physical Anthropology. 164 (1): 184–192. doi:10.1002/ajpa.23250. ISSN 1096-8644. PMID 28542710. S2CID 24296825.
  49. ^ Weiss & Mann (1985), pp. 130–135
  50. ^ Mai, Young Owl & 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.
  51. ^ "Palaeos Vertebrates > Bones > Teeth: Tooth Implantation". Palaeos: Life through Deep Time. Retrieved 30 November 2022.
  52. ^ Martin, A. J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. ISBN 1-4051-3413-5.

General references

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Further reading

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Dentition

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Dentition refers to the development, arrangement, type, and number of teeth in the mouth of vertebrates, encompassing structures that evolved as elements of the dermal skeleton in jawed species for functions such as feeding, grasping, and sensory detection.[1] In vertebrates, teeth typically consist of hard tissues including enamel or enameloid covering a core of dentin surrounding a pulp cavity with vascular and neural elements, with origins tracing back to odontodes—small, tooth-like dermal structures—predating the evolution of jaws in early forms like thelodonts and anaspids.[1] Vertebrate dentitions vary widely by lineage, classified by morphology (e.g., homodont, with uniform teeth, as in many fish and reptiles; heterodont, with specialized types like incisors, canines, premolars, and molars, typical in mammals), and by replacement pattern (e.g., monophyodont in most reptiles with a single set; diphyodont in mammals with deciduous and permanent generations; polyphyodont in fish and some reptiles with continuous replacement).[2] Evolutionarily, teeth likely arose through ectodermal invasion into the oropharyngeal cavity, interacting with neural crest-derived mesenchyme, with pharyngeal denticles representing an ancestral "inside-out" component later integrated into oral dentitions as jaws formed.[1] In mammals, including humans, dentition is predominantly heterodont and diphyodont, adapting to diverse diets through specialized tooth forms: incisors for cutting, canines for tearing, premolars for crushing, and molars for grinding.[3] Human primary (deciduous) dentition comprises 20 teeth—8 incisors, 4 canines, and 8 molars—that erupt between approximately 6 months and 3 years of age, providing initial masticatory function before replacement by the permanent set.[4] The permanent human dentition includes 32 teeth (excluding third molars in some individuals)—8 incisors, 4 canines, 8 premolars, and 12 molars—per quadrant formula of I:2/2, C:1/1, P:2/2, M:3/3, erupting from around 6 years through adolescence, supporting advanced mastication, speech articulation, and facial structure maintenance.[3] Anomalies in dentition, such as supernumerary teeth or agenesis, can affect occlusion and overall oral health,[5] while comparative studies across vertebrates reveal evolutionary adaptations like hypsodont (high-crowned) teeth in herbivores for abrasive diets[6] or acrodont (fused to jaw) forms in some lizards.[7] Overall, dentition exemplifies modular developmental genetics, with conserved pathways like those involving BMP, FGF, and Wnt signaling patterning tooth identity and succession across species.[1]

Fundamentals

Definition and Scope

Dentition refers to the complete set of teeth in an organism, encompassing their number, type, arrangement within the jaws, and overall condition.[8] This biological feature is essential for functions such as feeding, defense, and sensory perception, varying widely across species in morphology and replacement patterns.[9] The term "dentition" derives from the Latin dentitio, meaning "teething" or the process of tooth eruption, with early uses in English dating to the 17th century.[10] While primarily associated with vertebrates—where teeth are typically mineralized structures anchored to the maxilla and mandible—analogous feeding apparatuses exist in certain invertebrates, such as the radula of mollusks, a chitinous ribbon bearing rows of microscopic teeth for scraping food.[11] In mammals, dentition is generally diphyodont, featuring two generations of teeth: the primary (deciduous) set, which emerges during infancy and is later shed, and the permanent set that develops afterward to support adult functions.[3] This distinction highlights the adaptive replacement mechanism unique to many mammals, allowing for larger, more durable teeth suited to mature dietary needs.[12]

Terminology

In the study of dentition, key terms describe the morphological and developmental variations in teeth across vertebrates. Heterodont dentition refers to a condition where teeth differ in shape and function within the same jaw, typically featuring specialized types such as incisors for cutting, canines for tearing, premolars for crushing, and molars for grinding; this arrangement is characteristic of most mammals, including humans. The term derives from the Greek words heteros (different) and odous (tooth). In contrast, homodont dentition involves teeth that are uniform in shape and primarily conical, suited for grasping or piercing, as seen in many non-mammalian vertebrates like reptiles and most fish. This uniformity derives from Greek homos (same) and odous (tooth).[2][13][14] Developmental terminology further classifies dentition based on replacement patterns. Diphyodont describes animals that develop two successive sets of teeth: a primary (deciduous) set replaced by a permanent set, a pattern prevalent in mammals to accommodate growth. The term originates from Greek di- (two), phyein (to produce), and odous (tooth), with first use around 1854 in scientific literature. Conversely, polyphyodont dentition involves continuous replacement of teeth throughout life, often in multiple generations, as observed in sharks, reptiles, and some fish, allowing adaptation to wear or injury. This derives from Greek poly- (many), phyein (to produce), and odous (tooth). Monophyodont dentition refers to animals that develop only one set of teeth with no replacement, common in certain reptiles and some other vertebrates. The term derives from Greek mono- (one), phyein (to produce), and odous (tooth).[15][16][2] Tooth positions are standardized terms denoting specific locations and roles in the dental arch. Incisors are the anterior chisel-shaped teeth used for biting and cutting food, with eight in human adults (four maxillary, four mandibular). Canines, also called cuspids, are the pointed teeth adjacent to incisors, adapted for tearing, totaling four in humans. Premolars, or bicuspids, are posterior to canines and feature flattened surfaces for crushing and grinding, numbering eight in adults. Molars are the largest posterior teeth, designed for thorough mastication, with twelve in human adults including wisdom teeth. These positions are organized into four quadrants: the upper right (quadrant 1), upper left (quadrant 2), lower left (quadrant 3), and lower right (quadrant 4), dividing the mouth for precise identification.[17][18][19] Notation systems facilitate consistent communication in dental practice and research, particularly for humans. The FDI World Dental Federation numbering system, adopted internationally and approved by the World Health Organization, uses a two-digit format: the first digit indicates the quadrant (1 for upper right, 2 for upper left, 3 for lower left, 4 for lower right), and the second specifies the tooth position from 1 (central incisor) to 8 (third molar) in permanent dentition, or from 1 (central incisor) to 5 (second molar) in primary dentition using quadrants 5-8. In the United States, the Universal Numbering System employs sequential numbers from 1 to 32 for permanent teeth, starting at the upper right third molar (1), proceeding clockwise to the upper left third molar (16), then counterclockwise from the lower left third molar (17) to the lower right third molar (32); primary teeth use letters A-T in a similar clockwise pattern.[20][21][22] Related terms address alignment and attachment. Occlusion denotes the alignment and contact of upper and lower teeth during jaw closure or function, encompassing static (centric) and dynamic (chewing) relations essential for mastication and speech. Malocclusion refers to misalignment of teeth or jaws, such as overbite or crossbite, which can impair function or aesthetics and often requires orthodontic intervention. Ankylosis describes the abnormal fusion of a tooth's root (cementum or dentin) directly to the alveolar bone, eliminating the periodontal ligament and potentially causing eruption failure or occlusal issues.[23][24][25]

Dental Anatomy

Tooth Types and Functions

In mammals, dentition is characterized by heterodonty, where teeth are differentiated into distinct types adapted for specific functions in food processing.[6] The primary tooth types include incisors, canines, premolars, and molars, each contributing to the mechanical breakdown of food during mastication.[26] Incisors are chisel-shaped front teeth located at the anterior of the dental arcade, primarily functioning to cut and shear food items such as vegetation or flesh.[26] Canines, positioned lateral to the incisors, are conical and pointed, specialized for tearing and grasping prey or tough fibrous materials.[27] Premolars, situated between canines and molars, feature broader crowns with one or more cusps and serve to crush, shear, or slice food, aiding in initial grinding.[26] Molars, the posterior teeth, have large, flat occlusal surfaces with multiple cusps and are dedicated to grinding and pulverizing food into smaller particles for efficient swallowing and digestion.[26] These tooth types collectively initiate digestion by mechanically reducing food particle size, increasing surface area for enzymatic action in the gastrointestinal tract.[28] Tooth enamel, the outermost covering, provides durability with a hardness of 5 on the Mohs scale, enabling resistance to wear during repeated occlusal contacts.[29] Beyond mastication, teeth serve secondary roles in some mammals, such as grooming; for instance, incisors and specialized tooth combs in primates and hyraxes are used to comb fur and remove parasites.[30][31] Morphological variations in tooth shape reflect dietary adaptations across mammals. Cusps, the raised projections on occlusal surfaces, enhance shearing efficiency in carnivores with sharp, blade-like arrangements for slicing meat, while herbivores exhibit low, rounded cusps or flat lophs for grinding abrasive plant matter.[32] Fissures, the grooves between cusps, facilitate food trapping and trituration, with deeper patterns in omnivores promoting versatile processing.[33] Cingula, enamel shelves encircling the tooth base, provide structural reinforcement and additional cutting edges, particularly in early mammals adapted to mixed diets.[34] These features evolve to optimize fracture mechanics against specific food toughness, as seen in the multi-cusped molars of folivores versus the simplified forms in insectivores.[35]

Tooth Structure and Development

The tooth consists of four primary layers, each with distinct histological features and origins. Enamel, the outermost layer covering the crown, is ectodermal in origin and acellular, composed primarily of hydroxyapatite crystals arranged in rods that provide hardness but no regenerative capacity.[36] Dentin, forming the bulk of the tooth beneath the enamel, is mesodermal and tubular, consisting of about 70% mineral content with odontoblast processes extending through dentinal tubules that convey sensitivity to the pulp.[36] Cementum, a mesodermal layer covering the root surface, resembles bone in structure with embedded cementocytes and facilitates attachment to the periodontal ligament.[36] At the core lies the pulp, a mesodermal vascularized connective tissue housing nerves, blood vessels, and odontoblasts that supports dentin formation and vitality.[36] Tooth development, or odontogenesis, unfolds through sequential embryogenic stages beginning around the 6th week of intrauterine life. In the bud stage, epithelial thickenings from the dental lamina protrude into the underlying mesenchyme, initiating tooth germ formation under mesenchymal signaling.[37] The cap stage follows, where the enamel organ assumes a cap-like shape, differentiating the inner enamel epithelium into ameloblasts and inducing the dental papilla and follicle for hard tissue deposition.[37] During the bell stage, the enamel organ fully envelops the dental papilla, establishing the crown's final shape through epithelial-mesenchymal interactions, with the stellate reticulum and stratum intermedium supporting ameloblast function.[37] Amelogenesis and dentinogenesis are interdependent processes that produce the mineralized tissues. Dentinogenesis begins first, as inner enamel epithelium induces dental papilla cells to differentiate into odontoblasts, which secrete predentin that mineralizes into dentin via calcospherites coalescing into structured layers.[37] Amelogenesis then proceeds, with ameloblasts secreting an enamel matrix through Tomes' processes at the amelodentinal junction, followed by mineralization into hydroxyapatite prisms that mature as ameloblasts regress.[37] Eruption involves coordinated bone remodeling to guide the tooth into the oral cavity. The periodontal ligament plays a key role in the supraosseous phase by generating propulsive forces through collagen fiber shortening and cross-linking, facilitating occlusal movement.[38] Alveolar bone resorption, driven by osteoclasts activated by the dental follicle, creates the intraosseous pathway superior to the crown, while bone apposition occurs apically to maintain position.[38] Developmental abnormalities can disrupt these processes, leading to structural defects. Amelogenesis imperfecta arises from genetic mutations affecting enamel formation, resulting in hypoplastic or hypomineralized enamel that is thin, discolored, and prone to wear across all teeth.[39] Dentinogenesis imperfecta, caused by mutations in genes like DSPP, impairs dentin development, producing opaque, weakened teeth with obliterated pulp chambers and increased fracture risk.[40]

Human Dentition

Dental Formula

The dental formula is a standardized notation system used to summarize the number and arrangement of teeth in the human dentition by type and position.[8] It specifies the count of incisors (I), canines (C), premolars (P), and molars (M) present in one half of the upper jaw (maxilla) over the corresponding half of the lower jaw (mandible), with the total number of teeth obtained by multiplying the formula by two to reflect bilateral symmetry.[41] This method provides a concise representation of the dentition's composition without detailing individual tooth positions or eruption timing.[8] To calculate the dental formula, teeth are counted per quadrant—dividing the mouth into four sections (upper right, upper left, lower right, lower left)—focusing on one quadrant for the notation.[41] For example, in the permanent human dentition, each quadrant contains 2 incisors, 1 canine, 2 premolars, and 3 molars, yielding the formula I 2.C 1.P 2.M 3 × 2, or equivalently 2.1.2.3 × 2, for a total of 32 teeth.[8] The deciduous (primary) dentition follows a similar process but with 2 incisors, 1 canine, 0 premolars, and 2 molars per quadrant, resulting in 2.1.0.2 × 2, or 20 teeth total.[41] This counting assumes typical symmetry and serves as a reference for normal development across the four tooth types: incisors for incision, canines for puncture, premolars for crushing, and molars for grinding.[8] Notation variations exist between textual and graphical formats. The standard textual dental formula uses a dotted or slashed sequence, such as 2/2 1/1 2/2 3/3 for permanent dentition, separating upper and lower counts with a line.[41] In contrast, Palmer's graphical method employs quadrant symbols (e.g., ┐ for upper right, └ for lower left) combined with numbers (1-8 for permanent teeth, starting from the midline) to denote specific teeth, facilitating detailed charting rather than summary representation.[42] In clinical dentistry, the dental formula provides a foundational framework for identifying and documenting anomalies, such as agenesis (congenital absence of teeth, altering the count in affected categories) or supernumerary teeth (extra teeth beyond the standard formula).[8] Dentists use it to systematically record deviations during examinations, aiding in diagnosis, treatment planning, and communication of cases like hypodontia or hyperdontia.[43] This application underscores its role in forensic and orthodontic contexts, where deviations from the norm inform broader health assessments.[8]

Eruption Sequence and Naming

In human primary dentition, teeth begin erupting around 6 months of age, with the mandibular central incisors typically emerging first between 6 and 10 months.[44][45] The sequence generally follows mandibular central incisors, maxillary central incisors, lateral incisors, first molars, canines, and second molars, resulting in a full set of 20 primary teeth by approximately 2 to 3 years of age.[46][47] Permanent dentition commences with the eruption of the first molars around 6 years of age, followed by central incisors (6-8 years), lateral incisors and first premolars (8-9 years), canines and second premolars (10-12 years), second molars (11-13 years), and third molars (wisdom teeth) between 17 and 25 years.[38] Females generally experience earlier eruption than males across most permanent teeth, with differences of several months observed in timing.[47][48] Standard naming conventions facilitate precise identification of teeth, with the Fédération Dentaire Internationale (FDI) system—also known as the ISO 3950 notation—employing a two-digit code where the first digit denotes the quadrant (1 for upper right, 2 for upper left, 3 for lower left, 4 for lower right) and the second indicates the tooth position from 1 (central incisor) to 8 (third molar); for example, tooth 11 refers to the upper right central incisor.[49][50] This contrasts with the American Universal Numbering System, which sequentially numbers permanent teeth from 1 to 32 starting at the upper right third molar and proceeding clockwise, leading to discrepancies in international communication and documentation.[51][52] Several factors influence the eruption sequence and timing, including genetics, which determine baseline patterns; nutrition, where deficiencies such as in calcium or vitamins can delay emergence; and pathologies like endocrine disorders or systemic conditions that may postpone or alter the process.[53][54][55]

Comparative Dentition

Mammalian Variations

Mammalian dentition exhibits significant variations in tooth number, arrangement, and morphology, reflecting adaptations to diverse diets and lifestyles. The primitive dental formula for placental mammals, representing the ancestral condition, is 3 incisors, 1 canine, 4 premolars, and 3 molars per quadrant in both the upper and lower jaws (3.1.4.3/3.1.4.3), totaling 44 teeth.[56] This formula has undergone reductions in many lineages; for example, carnivores like dogs display a modified formula of 3.1.4.2/3.1.4.3, with fewer upper molars to accommodate shearing carnassials for meat processing.[6] In contrast, humans exhibit further reduction to 2.1.2.3/2.1.2.3 as a reference point for comparative heterodonty.[57] Tooth replacement patterns also vary among mammals, with most species being diphyodont, featuring two successive generations: deciduous teeth replaced by permanent ones, as seen in humans and many other therians.[58] However, monotremes, such as the platypus and echidna, lack functional adult dentition; the platypus has temporary teeth in juveniles that are resorbed before adulthood, while echidnas have no teeth and use grinding pads, adaptations linked to their specialized diets.[59] Some mammals, including certain rodents and lagomorphs, further modify this by having continuously erupting teeth to compensate for heavy wear. Dietary influences drive key morphological adaptations in crown height and structure. Grazing mammals, such as horses, typically have hypsodont (high-crowned) teeth with extended roots and continuous eruption, allowing prolonged use against abrasive forage like grasses.[6] In contrast, browsing species like deer possess brachydont (low-crowned) teeth suited to softer vegetation, with crowns that do not exceed root length and limited eruption.[60] These differences enhance occlusal efficiency and durability tailored to feeding ecology. Specialized dental features further illustrate mammalian diversity. Rodents feature ever-growing incisors driven by persistent stem cells at the cervical loop, enabling gnawing through hard materials without wear-down.[61] Elephants possess elongated tusks as modified upper incisors, composed primarily of dentin and used for foraging, defense, and manipulation, growing continuously throughout life.[62] Among cetaceans, odontocetes (toothed whales) have evolved numerous simple, conical teeth—often peg-like and homodont—for grasping slippery prey like fish and squid, with tooth counts varying widely from dozens to hundreds per jaw.[63]

Non-Mammalian Dentition

Non-mammalian dentition is characterized by polyphyodonty, where teeth are continuously replaced throughout life, and homodonty, in which teeth are generally uniform in shape and function across the jaw, contrasting with the diphyodont replacement and heterodonty typical of mammals.[64][65] This arrangement supports diverse feeding strategies in vertebrates such as fish, amphibians, reptiles, and birds, with teeth often adapted for grasping, piercing, or grinding rather than specialized occlusion.[66] In reptiles, dentition varies by implantation mode and replacement dynamics, with polyphyodonty enabling lifelong tooth renewal to maintain functionality. Acrodont teeth, fused directly to the crest of the jawbone, are prevalent in lizards such as agamids and chameleons, providing a stable anchorage but limiting individual tooth mobility and replacement.[67] Pleurodont teeth, attached to the medial or lateral surface of the jaw, occur in snakes and many lizards, allowing for more flexible eruption and continuous substitution as worn teeth are shed lingually.[68] This side-fused structure facilitates the resorption and regeneration cycles characteristic of reptilian polyphyodonty, where successional teeth develop asynchronously to ensure uninterrupted feeding capability.[69] Fish exhibit highly diverse dentition adapted to aquatic environments, often featuring homodont arrangements of simple, conical teeth distributed across multiple jaw elements, including pharyngeal arches. Pharyngeal teeth, located on the gill arches, process food after initial capture by oral teeth and vary from crushing forms in herbivorous species to pointed types in carnivores.[70] Cardiform teeth, small and comb-like in rows, aid in raking and holding slippery prey, as seen in gars and many predatory teleosts.[71] Villiform teeth, resembling dense brushes of fine points, function similarly for grasping and piercing, enhancing grip on evasive aquatic organisms in species like catfishes and perches.[72] Polyphyodont replacement in fish ensures rapid turnover, with teeth forming in lingual successional rows that migrate occlusally as predecessors are lost.[64] Birds represent a notable exception among non-mammalian vertebrates, having completely lost teeth during their evolution, with the rhamphotheca—a keratinous sheath—replacing dentition as the primary feeding structure.[73] This edentulous condition, achieved by the suppression of odontogenic pathways, allows for lightweight skulls optimized for flight, while the beak's horny covering enables diverse functions from cracking seeds to tearing flesh.[74] Fossil evidence from Mesozoic avialans, such as Archaeopteryx, reveals ancestral toothed dentitions with conical, recurved teeth suited for carnivory, indicating that tooth loss occurred multiple times within bird lineages but was irreversible in modern forms.[75] Amphibians display varied dentition, with frogs featuring pedicellate teeth that consist of a calcified base fused to the jaw and a separate, often bicuspid crown connected by an unmineralized zone, facilitating individual tooth replacement.[76] This two-part structure predominates on the upper jaw bones—premaxillae, maxillae, and vomers—serving to grasp and hold prey during ingestion, while the labile crown design supports polyphyodonty through periodic shedding.[77] In contrast, salamanders retain more uniform, homodont teeth across both jaws, and caecilians possess robust, recurved teeth for burrowing and predation, though tooth loss has evolved independently over 20 times in anuran lineages.[77]

Evolutionary and Applied Aspects

Evolutionary History

The evolutionary origins of dentition trace back to the early vertebrates in the Cambrian period, approximately 500 million years ago, where conodonts represent some of the earliest known dental elements. These microscopic, tooth-like structures, composed of dentine and enamel, are thought to have functioned in feeding or sensory roles within the oral cavity of ancient chordates.[78] The development of true teeth is believed to have evolved from external skin denticles, or odontodes, which were dermal structures providing protection and possibly sensory functions in primitive fish-like vertebrates; over time, these odontodes internalized and specialized within the mouth, marking a key transition from exoskeletal armor to oral dentition.[1] A significant advancement occurred in the archosaur lineage during the late Permian to early Triassic, around 250 million years ago, with the evolution of thecodont implantation, where teeth became deeply socketed in the jawbones for enhanced stability during biting and tearing. This adaptation is characteristic of early archosaurs and their descendants, including crocodilians, which retain it today. However, teeth were subsequently lost in several archosaur groups, notably birds and some reptiles like turtles, likely due to shifts toward beak-like structures for efficient processing of food without the need for replaceable dentition; non-mammalian polyphyodonty, involving continuous tooth replacement, persisted in many reptilian lineages.[79][80] Among extinct archosaurs, dinosaurs exhibited remarkable dental diversity adapted to their ecological niches. Theropod dinosaurs, such as Tyrannosaurus rex, displayed heterodont dentition with conical, recurved teeth featuring serrated edges akin to carnassial blades, enabling them to slice through flesh efficiently. In contrast, herbivorous ornithischians, including hadrosaurs and ceratopsians, evolved complex dental batteries comprising hundreds of tightly packed, self-sharpening teeth that formed grinding surfaces for processing tough plant material, representing a pinnacle of dental specialization in Mesozoic reptiles.[81][82] The post-Triassic radiation of mammals, beginning around 200 million years ago, saw the refinement of heterodonty, with distinct incisors, canines, premolars, and molars enabling specialized functions like cutting, piercing, and grinding to support increasingly varied diets in terrestrial environments. This dental complexity arose from synapsid ancestors and contributed to mammalian diversification by facilitating efficient resource exploitation.[83][84]

Archaeological and Forensic Uses

Dentition analysis plays a crucial role in archaeology by providing insights into the age, diet, health, and population affiliations of ancient human remains. Through examination of tooth eruption, wear patterns, and morphological traits, researchers reconstruct aspects of prehistoric lifeways, such as subsistence strategies and social structures. In forensics, dental evidence facilitates victim identification and crime scene analysis, leveraging unique tooth characteristics and preserved biological material for legal purposes.[85] Age estimation in archaeological contexts often relies on tooth eruption sequences for subadults and wear patterns for adults, with methods like the Gustafson technique assessing regressive changes such as secondary dentin deposition, cementum apposition, root resorption, and dentin translucency to predict age at death. Developed in 1949, Gustafson's method scores these features on a scale to estimate adult ages with reasonable accuracy, particularly when combined with histological analysis, and has been validated in studies of known-age samples from various populations. In forensic applications, these techniques help determine the biological profile of unidentified remains, aiding in narrowing search parameters for missing persons.[86][87][85] Dietary reconstruction from ancient teeth employs dental microwear analysis, which examines microscopic pits and scratches on enamel surfaces to infer food types; for instance, large pits suggest tough, abrasive foods like meat or seeds, while fine scratches indicate grassy or leafy vegetation. This approach has revealed shifts from hunter-gatherer to agricultural diets in Neolithic populations, as seen in European skeletal samples where microwear patterns correlate with increased grain consumption. Complementing microwear, stable isotope analysis of tooth enamel measures ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) to determine trophic levels and plant sources; elevated δ¹⁵N values indicate higher protein intake from animal sources, while δ¹³C distinguishes C₃ (e.g., wheat, trees) from C₄ (e.g., maize, millet) pathways, enabling paleodietary profiling in contexts like ancient Egyptian or Andean remains.[88][89][90][91] Tooth morphology aids in estimating ancestry and population affinity in bioarchaeological studies by analyzing non-metric traits like shovel-shaped incisors or Carabelli's cusp, which vary systematically across groups and reflect genetic heritage. For example, multivariate statistical models applied to dental phenotypes from prehistoric European sites have traced migration patterns and admixture events over millennia. Pathological evidence, such as abscesses from untreated caries or periodontal disease, appears frequently in prehistoric skulls, indicating poor oral hygiene and dietary stressors; a two-million-year-old Paranthropus robustus specimen from South Africa showed maxillary abscesses linked to heavy wear from abrasive foods. Trepanation, an ancient cranial surgery sometimes associated with relieving dental-related headaches or infections, is evidenced in healed skull perforations from Iron Age Iranian remains, where proximity to abscessed teeth suggests therapeutic intent.[92][93][94][95] In forensic odontology, bite mark analysis compares class characteristics (e.g., arch width, tooth alignment) and individual traits (e.g., unique fractures or spacing) from impressions on skin, food, or objects to suspect dentitions, though its reliability is debated due to tissue distortion. Successful applications include linking bites to perpetrators in assault cases, as documented in American Board of Forensic Odontology guidelines. Additionally, DNA extraction from dental pulp provides high-quality genetic material for identification, even in degraded remains; pulp's protected location within dentin and enamel yields sufficient nuclear DNA for STR profiling, as demonstrated in disaster victim identification efforts where teeth survived incineration.[96][97][98][99]

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