AskDefine | Define molars

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Noun

molars
  1. Plural of molar

Extensive Definition

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone".

Human molars

Adult humans have twelve molars, in four groups of three at the back of the mouth. The third (rearmost) molar in each group is called a wisdom tooth. It is the last tooth to appear, breaking through the surface of the gum at about the age of twenty, although this varies from individual to individual. Ethnicity can also have an impact on the age at which this occurs, with statistical variations between groups.

Molars among species

Molars differ considerably from one species to another, so there are many terms describing them:
  • Tribosphenic: This kind is found in insectivores and young platypuses (adults have no teeth). Upper molars look like three-pointed mountain ranges; lowers look like two peaks and a third off to the side.
  • Quadrate: This kind is found in humans and various other species. Four cusps are arranged in a rectangle; there may be a fifth.
  • Bunodont: The cusps, instead of being sharp peaks, are rounded hills. The entire tooth is covered in enamel, and is most common among omnivores such as the pig, the bear and humans.
  • Hypsodont: There is a lot of enamel and dentine above the gumline and the top of the pulp. This kind of molar is found in mammals that wear their teeth a lot, such as the horse.
  • Zalambdodont: The tooth has two ridges that meet at an angle, forming the letter lambda.
  • Dilambdodont: Like zalambdodont, but there are two lambdas on one tooth.
  • Lophodont: The tooth has a few ridges perpendicular to the jaw.
  • Selenodont: The tooth has a crescent-shaped ridge or ridges.
  • Loxodont: The tooth has several parallel oblique ridges on its surface. The elephant Loxodonta is named for this feature.

Tribosphenic molar

The molar design that is considered one of the most important characteristics of mammals is a three-cusped shape called a tribosphenic molar. This design of molar has two important features: the trigonid, or shearing end, and the talonid, or crushing heel. In modern mammals that have tribosphenic molars the trigonid is towards the front and the talonid towards the rear.
The tribosphenic design appears in all groups of mammals. Some paleontologists believe that it developed independently in monotremes, rather than being inherited from an ancestor that they share with with marsupials and placentals; but this idea has critics and the debate is still going on.
Also some Jurassic mammals, such as Shuotherium and Pseudotribos, have "reversed tribosphenic" molars in which the the talonid is towards the front. This variant is regarded as an example of convergent evolution

Additional images

Image:Teeth_molar47_46resection_crown_premolar45.jpg|Molar 47 (left), molar 46 and premolar 45(right) Image:Illu mouth.jpg|Mouth (oral cavity)

References

External links

For pictures of various molars see The Diversity of Cheek Teeth.
molars in Catalan: Queixal
molars in Czech: Stolička
molars in Danish: Kindtand
molars in German: Molar (Zahn)
molars in Spanish: Molar
molars in Esperanto: Vangodento#Molaro
molars in French: Molaire (dent)
molars in Indonesian: Gigi geraham
molars in Italian: Molare
molars in Hebrew: שן טוחנת
molars in Dutch: Molaar
molars in Dutch Low Saxon: Koeze
molars in Japanese: 大臼歯
molars in Norwegian: Jeksler
molars in Polish: Ząb trzonowy
molars in Portuguese: Molar
molars in Simple English: Molar
molars in Serbian: Кутњаци
molars in Finnish: Poskihammas
molars in Swedish: Molarer
molars in Telugu: చర్వణకాలు
molars in Chinese: 大臼齿
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