thumb|335px|Cast of a human upper jaw showing [[incisors, canines, premolars, and two of the three possible pairs 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, 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). 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."

Dental formula

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. ||<br />

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| Kangaroo || ||<br />

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| Musky rat-kangaroo || ||<br />

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| Rest of Potoroidae || ||<br />

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| Opossum || ||<br />

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!colspan="2" scope="row"| Placental||Some examples of dental formulae for placental mammals.

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|Apes || || All apes (excluding 20–23% of humans) and Old World monkeys share this formula, sometimes known as the cercopithecoid dental formula. ||<br />

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|Big brown bat||||<br />

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|Cat (deciduous)|||| 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.<br />

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|Dog (deciduous)||||<br />

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|Dog (permanent)||||<br />

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|Eulemur|| ||Prosimian genus to which the large Malagasy or 'true' lemurs belong.||<br />

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|Hedgehog||

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|Indri||See comment||A prosimian. Dental formula disputed. Either or . Proponents of both formulae agree there are 30 teeth and that there are only four teeth in the dental comb. ||<br />

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|Mole||

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|New World monkeys ||See comment||All New World monkeys have a dentition formula of or .

|Extinct suborder of early eutherians.

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|Pig (deciduous)|| 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.

See also

  • Deciduous teeth
  • Dental notation
  • Dentistry
  • Dentition analysis
  • Odontometrics
  • Permanent teeth
  • Phalangeal formula
  • Teething
  • Tooth eruption

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

  • African bush elephant
  • Canidae
  • Red fox
  • Lemur
  • Manatee
  • Ungulate

Citations

General references

Further reading

  • See also preview pages in Google books
  • (link provided to title page to give reader choice of scrolling straight to relevant chapter or perusing other material).
  • Colorado State's Dental Anatomy Page
  • For image of skulls and more information on dental formula of mammals.

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