Dentition

Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is 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 (that is, the relationship between the shape and form of the tooth in question and its inferred function) 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 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.

Upper Jaw Dentition.jpeg
Cast of a human upper jaw showing incisors, canines, premolars, and 2 of the 3 possible sets of molars.

Overview

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 450mya, 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 shearing the food caught between."[5]

All mammals except the monotremes, the xenarthrans, the pangolins, and the cetaceans have up to four distinct types of teeth, with a maximum number for each. 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. 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.

Dental formula

Because mammal 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.[9]

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.[9][10] 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.[10]

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.[10][11] 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. '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[10]
  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 was 48, with a formula of 3.1.5.33.1.5.3.[9] However, no existing (or extant) placental mammal has this number. In extant placental mammals, the maximum dental formula is: 3.1.4.33.1.4.3. Mammal teeth are usually symmetrical, 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.[10]

Tooth naming discrepancies

Teeth are numbered starting at 1 in each group. Thus the human teeth are I1, I2, C1, P3, P4, M1, M2, and M3.[12] (See next paragraph for premolar naming etymology.) In humans, the third molar is known as the wisdom tooth, whether or not it has erupted.[13]

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

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.[12]

Dental formulae examples

Some examples of mammalian dental formulae[14]
Species Dental formula Comment
Non placental . Non-placental mammals such as marsupials (e.g., opossums) can have more teeth than placentals.
Kangaroo 3.1.2.41.0.2.4[15]
Musky rat-kangaroo 3.1.1.42.0.1.4[16]
Rest of Potoroidae 3.1.1.41.0.1.4[16] 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 [17]
Opossum 5.1.3.44.1.3.4 [18]
Placental . Some examples of dental formulae for placental mammals.
Armadillo 0.0.7.10.0.7.1[19]
Aye-aye 1.0.1.31.0.0.3[20] A prosimian. The aye-aye's deciduous dental formula (dI:dC:dM) is 2.1.22.1.2.[10]
Badger 3.1.3.13.1.3.2[21]
Big brown bat 2.1.1.33.1.2.3[18]
Red bat, hoary bat, Seminole bat, Mexican free-tailed bat 1.1.2.33.1.2.3[18]
Cat (deciduous) di3.dc1.dp3.dm0di3.dc1.dp2.dm0[22]
Cat (permanent) 3.1.3.13.1.2.1[11] 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.
Chimpanzee 2.1.2.32.1.2.3 All apes (excluding 20–23% of humans) and Old World monkeys (excluding Prosimii) share this formula, sometimes known as the cercopithecoid dental formula.[13]
Cow 0.0.3.33.1.3.3[23] 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) di3.dc1.dp3.dm0di3.dc1.dp3.dm0[22]
Dog (permanent) 3.1.4.23.1.4.3[21]
Eulemur 3.1.3.33.1.3.3 Prosimian genus to which the large Malagasy or 'true' lemurs belong.[24] Ruffed lemurs (genus Varecia),[25] dwarf lemurs (genus Mirza),[26] and mouse lemurs (genus Microcebus) also have this dental formula, but the mouse lemurs have a dental comb.[27]
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.[24]
Fox (red) 3.1.4.23.1.4.3[21]
Guinea pig 1.0.1.31.0.1.3[28]
Hedgehog 3.1.3.32.1.2.3[21]
Horse (deciduous) di3.dc0.dp3.dm0di3.dc0.dp3.dm0[29][30]
Horse (permanent) 3.0-1.3-4.33.0-1.3.3 Permanent dentition varies from 36–42, depending on the presence or absence of canines and the number of premolars.[31] The first premolar (wolf tooth) may be absent or rudimentary,[29][30] and is mostly present only in the upper (maxillary) jaw.[30] The canines are small and spade-shaped, and usually present only in males.[31] Canines appear in 20–25% of females and are usually smaller than in males.[30][32]
Human (deciduous teeth) di2.dc1.dp2di2.dc1.dp2
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.[33]
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.[34]
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.[35]
Lion 3.1.3.13.1.2.1[36]
Mole 3.1.4.33.1.4.3[21]
Mouse (House) 1.0.0.31.0.0.3[21] Plains pocket mouse (Perognathus flavescens) have dental formula of 1.0.1.31.0.1.3.[37]
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.[13]
Pig (deciduous) di3.dc1.dp4.dm0di3.dc1.dp4.dm0[22]
Pig (permanent) 3.1.4.33.1.4.3[21]
Rabbit 2.0.3.31.0.2.3[11]
Raccoon 3.1.4.23.1.4.2
Rat 1.0.0.31.0.0.3[21]
Sheep (deciduous) di0.dc0.dp3.dm0di4.dc0.dp3.dm0[22]
Sheep (permanent) 0.0.3.33.1.3.3[18]
Shrew 3.1.3.33.1.3.3[21]
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.[38]
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.[39][40]
Squirrel 1.0.2.31.0.1.3[21]
Tarsiers 2.1.3.31.1.3.3 Prosimians.[41]
Vole (field) 1.0.0.31.0.0.3[21]
Weasel 3.1.3.13.1.3.2[21]

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.[42][43][44] 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

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 alveoli. These differ from teeth of other vertebrates, which are directly fused to the bones of the jaw. 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 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.[45]

See also

Dentition discussions in other articles

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

Notes

  1. ^ Angus Stevenson, ed. (2007), "Dentition definition", Shorter Oxford English Dictionary, 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.
  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. ^ a b c Weiss & Mann (1985), p. 134
  10. ^ a b c d e f Mai, Young Owl & Kersting (2005), p. 139
  11. ^ a b c Martin (1983), p. 102
  12. ^ a b Mai, Young Owl & Kersting (2005), p. 139. See section on dental eruption sequence, where numbering used is per this text.
  13. ^ 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
  14. ^ Unless otherwise stated, the formulae can be assumed to be for adult, or permanent dentition.
  15. ^ "Kangaroo". www.1902encyclopedia.com. Archived from the original on 4 July 2017. Retrieved 28 March 2018.
  16. ^ 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
  17. ^ University Of Edinburgh Natural History Collection, archived from the original on 2012-03-01
  18. ^ a b c d Dental formulae of mammal skulls of North America, Wildwood Tracking, archived from the original on 2011-04-14
  19. ^ 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
  20. ^ Mai, Young Owl & Kersting (2005), pp. 134,139
  21. ^ 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.
  22. ^ a b c d "Dental formulae". www.provet.co.uk. Retrieved 28 March 2018.
  23. ^ "Using Dentition to Age Cattle". fsis.usda.gov. Archived from the original on 2008-09-16. Retrieved 2008-09-06.
  24. ^ a b Mai, Young Owl & Kersting (2005), p. 177
  25. ^ Mai, Young Owl & Kersting (2005), p. 550
  26. ^ Mai, Young Owl & Kersting (2005), p. 340
  27. ^ Mai, Young Owl & Kersting (2005), p. 335
  28. ^ Noonan, Denise. "The Guinea Pig (Cavia porcellus)" (PDF). ANZCCART. Archived (PDF) from the original on 2016-08-04.
  29. ^ a b Pence (2002), p. 7
  30. ^ a b c d Cirelli
  31. ^ a b Ultimate Ungulates
  32. ^ 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.
  33. ^ 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.
  34. ^ Mai, Young Owl & Kersting (2005), p. 267
  35. ^ Mai, Young Owl & Kersting (2005), p. 300
  36. ^ "Dental Formula". www.geocities.ws. Archived from the original on 28 February 2017. Retrieved 28 March 2018.
  37. ^ "Plains Pocket Mouse (Perognathus flavescens)". www.nsrl.ttu.edu. Archived from the original on 7 October 2017. Retrieved 28 March 2018.
  38. ^ Mai, Young Owl & Kersting (2005), p. 438
  39. ^ Mai, Young Owl & Kersting (2005), p. 309
  40. ^ Mai, Young Owl & Kersting (2005), p. 371
  41. ^ Mai, Young Owl & Kersting (2005), p. 520
  42. ^ Towle, Ian; Irish, Joel D.; Groote, Isabelle De (2017). "Behavioral inferences from the high levels of dental chipping in Homo naledi". American Journal of Physical Anthropology. 164 (1): 184–192. doi:10.1002/ajpa.23250. ISSN 1096-8644.
  43. ^ Weiss & Mann (1985), pp. 130–135
  44. ^ 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.
  45. ^ Martin, A. J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. ISBN 1-4051-3413-5.

References

  • Adovasio, J. M.; Pedler, David (2005), "The peopling of North America", in Pauketat, Timothy R.; Loren, Diana DiPaolo, North American Archaeology, Blackwell Publishing, pp. 35–36, ISBN 978-0-631-23184-4
  • Cirelli, Al, Equine Dentition (PDF), Nevada: University of Nevada, retrieved 7 June 2010
  • Mai, Larry L.; Young Owl, Marcus; Kersting, M. Patricia (2005), The Cambridge Dictionary of Human Biology and Evolution, Cambridge & New York: Cambridge University Press, ISBN 978-0-521-66486-8
  • Martin, E. A. (1983), Macmillan Dictionary of Life Sciences (2nd revised ed.), London: Macmillan Press, ISBN 978-0-333-34867-3
  • Pence, Patricia (2002), Equine Dentistry: A Practical Guide, Baltimore: Lippincott Williams & Wilkins, ISBN 978-0-683-30403-9
  • Swindler, Daris R. (2002), Primate Dentition: An Introduction to the Teeth of Non-human Primates (PDF), Cambridge: Cambridge University Press, ISBN 978-0-521-65289-6
  • Ultimate Ungulates, Family Equidae: Horses, asses, and zebras, Ultimate Unqulate.com, retrieved 7 June 2010
  • Weiss, M. L.; Mann, A. E. (1985), Human Biology and Behaviour: An Anthropological Perspective (4th ed.), Boston: Little Brown, ISBN 978-0-673-39013-4

Further reading

External links

Barodontalgia

Barodontalgia, commonly known as tooth squeeze, is a pain in tooth caused by a change in ambient pressure. The pain usually ceases at ground level. Dental barotrauma is a condition in which such changes in barometric pressure changes cause damage to the dentition.

The most common victims are underwater divers because in deep dives pressures can increase by several atmospheres, and military pilots because of rapid changes.

In pilots, barodontalgia may be severe enough to cause premature cessation of flights.Most of the available data regarding barodontalgia is derived from high-altitude chamber simulations rather than actual flights. Barodontalgia prevalence was between 0.7% and 2% in the 1940s, and 0.3% in the 1960s.Similarly, cases of barodontalgia were reported in 0.3% of high altitude-chamber simulations in the Luftwaffe.The rate of barodontalgia was about 1 case per 100 flight-years in the Israeli Air Force. During World War II, about one-tenth of American aircrews had one or more episodes of barodontalgia. In a recent study, 8.2% of 331 Israeli Air Force aircrews, reported at least one episode of barodontalgia.Barodontalgia is a symptom of dental disease, for example inflammatory cyst in the mandible.

Indeed, most of the common oral pathologies have been reported as possible sources of barodontalgia: dental caries, defective tooth restoration, pulpitis, pulp necrosis, apical periodontitis, periodontal pockets, impacted teeth, and mucous retention cysts. One exception is barodontalgia manifested as referred pain from barosinusitis or barotitis-media. The latter two conditions are generated from pressure changes rather than pressure-related flare-up of pre-existing conditions. A meta-analysis of studies conducted between 2001 and 2010 revealed a rate of 5 episodes/1,000 flight-years. Maxillary and mandibular dentitions were affected equally in flight, but in diving, maxillary dentition was affected more than the mandibular dentition, which can indicate a greater role for maxillary sinus pathology in diving barodontalgia. Surprisingly, despite cabin pressurization, the current in-flight barodontalgia incidence is similar to the incidence in the first half of the 20th century. Also, despite the greater fluctuation in divers' pressures, the weighted incidence of barodontalgia among aircrews is similar to the weighted incidence among divers. Furthermore, contrary to common belief, and in contrast to diving conditions, the role of facial barotrauma in the cause of in-flight barodontalgia is only minor (about one-tenth of cases).

Deciduous teeth

Deciduous teeth, commonly known as milk teeth, baby teeth and temporary teeth, are the first set of teeth in the growth development of humans and other diphyodont 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 teeth, but in the absence of permanent replacements, they can remain functional for many years.

Dentition analysis

Dentition analyses are systems of tooth and jaw measurement used in orthodontics to understand arch space and predict any malocclusion (mal-alignment of the teeth and the bite). Example systems of dentition analysis are listed below.

Heterodont

In anatomy, a heterodont (from Greek, meaning "different teeth") is an animal which possesses more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines ("eyeteeth"), premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding and or hunting specialization in a species. In contrast, homodont dentition refers to a set of teeth that possess the same tooth morphology.

In invertebrates, the term heterodont refers to a condition where teeth of differing sizes occur in the hinge plate, a part of the Bivalvia. In vertebrates, however, heterodont pertains to animals where teeth are differentiated into different forms such as incisors, canines, premolars, and molars.

Human skeleton

The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

The human skeleton performs six major functions; support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation.

The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology of the skull, dentition, long bones, and pelvis exist. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The human female pelvis is also different from that of males in order to facilitate childbirth. Unlike most primates, human males do not have penile bones.

Hypodontia

Hypodontia is defined as the developmental absence of one or more teeth (excluding the third molars) which can affect both the primary and permanent dentition. It is the most common developmental dental anomaly and can be challenging to manage clinically. The term hypodontia is used to describe the whole range of the disorder from one missing tooth to the complete absence of all teeth, anodontia.

Terminology in use varies. One text has proposed the following descriptive terms:

Hypodontia: A developmental or congenital condition characterised by fewer than normal teeth.

Severe hypodontia: A developmental or congenital condition characterised by absence of 6 or more teeth.

Oligodontia: A developmental or congenital condition characterised by fewer than normal teeth in the presence of systemic manifestations.

Anodontia: a developmental or congenital condition characterised by absence of all teeth.The descriptive terms agenesis or multiple dental agenesis are often used in the US.Individuals with hypodontia often exhibit other dental anomalies such as microdontia, impaction of permanent canines and transposition,Supernumerary teeth are teeth present in addition to the normal complement. This can occur in both dentitions.

Hypsodont

Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritty, fibrous material. The opposite condition is called brachydont.

Lepidosauromorpha

Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs (which include crocodiles and birds). The only living sub-group is the Lepidosauria: extant lizards, snakes, amphisbaenians and tuataras.

Lepidosauromorpha are distinguishable from Archosauromorphs (archosaurs) by their primitive sprawling gait, which allows for the same sinusoidal trunk and tail movement seen in fish, the sliding "joint" between the coracoids and the sternum (for a longer stride), and their pleurodont dentition. In contrast, Archosauromorphs possess a parasagittal gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, and a more thecodont dentition.

Lepidosauromorpha have retained cold blood because of their low-energy sprawling stance.

Mitridae

Mitridae, known as mitre shells, are a taxonomic family of sea snails, widely distributed marine gastropod molluscs in the clade Mitroidea.Both the Latin name and the common name are taken from the item of ecclesiastical headgear, the mitre or miter, used in reference to the shape of the shells.

The dentition of radula in the Mitroidea is rachiglossate, with well-developed central and lateral teeth, both comb-like.

Möbius syndrome

Möbius syndrome (also spelled Moebius) is an extremely rare congenital neurological disorder which is characterized by facial paralysis and the inability to move the eyes from side to side. Most people with Möbius syndrome are born with complete facial paralysis and cannot close their eyes or form facial expressions. Limb and chest wall abnormalities sometimes occur with the syndrome. People with Möbius syndrome have normal intelligence, although their lack of facial expression is sometimes incorrectly taken to be due to dullness or unfriendliness. It is named for Paul Julius Möbius, a German neurologist who first described the syndrome in 1888.

Neonatal teeth

Natal teeth are teeth that are present above the gumline (have already erupted) at birth, and neonatal teeth are teeth that emerge through the gingiva during the first month of life (the neonatal period).The incidence of neonatal teeth varies considerably, between 1:700 and 1:30,000 depending on the type of study; the highest prevalence is found in the only study that relies on personal examination of patients.Natal teeth, and neonatal teeth, can be the baby's normal deciduous teeth, sprouting prematurely. These should be preserved, if possible. Alternately, they could be supernumary teeth, extra teeth, not part of the normal allotment of teeth.

Open bite malocclusion

Open bite is a type of orthodontic malocclusion which has been estimated to occur in 0.6% of the people in the United States. This type of malocclusion has no vertical overlap or contact between the anterior incisors. The prevalence varies between different populations, for instance, occurring with 16% in black people and 4% in white people. The term "open bite" was coined by Carevelli in 1842.

Overbite

Overbite medically refers to the extent of vertical (superior-inferior) overlap of the maxillary central incisors over the mandibular central incisors, measured relative to the incisal ridges.The term overbite does not refer to a specific condition, nor is it a form of malocclusion. Rather an absent or excess overbite would be a malocclusion. Normal overbite is not measured in exact terms, but as a proportion (approximately 30–50% of the height of the mandibular incisors) and is commonly expressed as a percentage.

Paraenhydrocyon

Paraenhydrocyon ("beside Enhydrocyon") is an extinct genus of bone crushing omnivorous mammal similar to a dog of the family Canidae which inhabited North America during the Oligocene living from 33.3—20.6 Ma and existed for approximately 12.7 million years.

Though a carnivore, dentition suggests this animal was a hypercarnivore or mesocarnivore.

Permanent teeth

Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.

Snake skeleton

A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.

Tooth eruption

Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligament plays an important role in tooth eruption. The first human teeth to appear, the deciduous (primary) teeth (also known as baby or milk teeth), erupt into the mouth from around 6 months until 2 years of age, in a process known as "teething". These teeth are the only ones in the mouth until a person is about 6 years old creating the primary dentition stage. At that time, the first permanent tooth erupts and begins a time in which there is a combination of primary and permanent teeth, known as the mixed dentition stage, which lasts until the last primary tooth is lost. Then, the remaining permanent teeth erupt into the mouth during the permanent dentition stage.

Tooth gemination

Tooth gemination is a dental phenomenon that appears to be two teeth developed from one. There is one main crown with a cleft in it that, within the incisal third of the crown, looks like two teeth, though it is not two teeth. The number of the teeth in the arch will be normal.

Tooth resorption

Root resorption is the progressive loss of dentine and cementum by the action of osteoclasts. This is a physiological process in the exfoliation of the primary dentition, caused by osteoclast differentiation due to pressure exerted by the erupting permanent tooth. However, in the secondary dentition the process is pathological.

Precursor cells
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Pulp occlusion

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