Molar (tooth)


Molar (tooth)
Molars
Lower wisdom tooth.jpg
A lower wisdom tooth after extraction.
Gray997.png
Permanent teeth of right half of lower dental arch, seen from above.
Latin dentes molares
Gray's subject #242 1118
Artery posterior superior alveolar artery
Dorlands/Elsevier Molar teeth

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".

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.

The human mouth contains upper (maxillary) and lower (mandibular) molars. They are: maxillary first molar, maxillary second molar, maxillary third molar, mandibular first molar, mandibular second molar, and mandibular third molar.

Contents

Molars among species

  • 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 molar design 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 marsupials and placentals; but this idea has critics and the debate is still going on.[1]

Also some Jurassic mammals, such as Shuotherium and Pseudotribos, have "reversed tribosphenic" molars in which the talonid is towards the front. This variant is regarded as an example of convergent evolution.[2]

Pathology


Additional images

See also

References

External links

For pictures of various molars see The Diversity of Cheek Teeth.


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Look at other dictionaries:

  • molar tooth — noun see molar I, 1 …   Useful english dictionary

  • molar tooth — wide tooth on the side of the mouth whose job it is to break apart the food …   English contemporary dictionary

  • molar tooth third — the tooth most distal to the medial line on either side in each jaw, so called because it is the last of the permanent dentition to erupt, usually at the age of 17 to 21 years. Called also wisdom t., third molar, dens molaris tertius [TA], and… …   Medical dictionary

  • Molar — may refer to: Molar (tooth), the fourth kind of tooth in mammals Molar (grape), another name for the Spanish wine grape Listan Negro Molar concentration, a unit of concentration, or molarity, of solutions equal to 1 mole per litre Molar volume El …   Wikipedia

  • molar — molar1 [mō′lər] adj. [L molaris, a mill < mola, millstone: see MILL1] 1. used for or capable of grinding 2. designating or of a tooth or teeth adapted for grinding n. a molar tooth: in humans there are usually twelve permanent molars, three on …   English World dictionary

  • Molar Massif — (71°38′S 163°45′E / 71.633°S 163.75°E / 71.633; 163.75) is a large mountain massif immediately east of Lanterman Range in the Bowers Mountains. Mapped by United State …   Wikipedia

  • Tooth development — Radiograph of lower right (from left to right) third, second, and first molars in different stages of development. Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth …   Wikipedia

  • molar — molar1 /moh leuhr/, n. 1. Also called molar tooth. a tooth having a broad biting surface adapted for grinding, being one of twelve in humans, with three on each side of the upper and lower jaws. See illus. under tooth. adj. 2. adapted for… …   Universalium

  • molar — n. Grinder, grinding tooth, molar tooth, double tooth, mill tooth …   New dictionary of synonyms

  • molar — molar1 (also molar tooth) noun a grinding tooth at the back of a mammal s mouth. Origin ME: from L. molaris, from mola millstone . molar2 adjective acting on or by means of large masses or units. Origin C19: from L. moles mass + ar1. molar3… …   English new terms dictionary


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