Molar (tooth)
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{{Infobox Anatomy |
Name = Molar |
Latin = dentes molares |
GraySubject = 242 |
GrayPage = 1118 |
Image = Lower wisdom tooth.jpg |
Caption = A lower [[wisdom tooth]] after extraction. |
Image2 = Gray997.png |
Caption2 = Permanent teeth of right half of lower dental arch, seen from above. |
Precursor = |
System = |
Artery = [[posterior superior alveolar artery]] |
Vein = |
Nerve = |
Lymph = |
MeshName = |
MeshNumber = |
DorlandsPre = d_08 |
DorlandsSuf = 12285848 |
}}
'''Molars''' are the rearmost and most complicated kind of [[tooth]] in most [[mammal]]s. 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 teeth|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 types of molars in the human mouth are:
* [[maxillary first molar]]s, [[maxillary second molar]]s, and [[maxillary third molar]]s
* [[mandibular first molar]]s, [[mandibular second molar]]s, and [[mandibular third molar]]s
==Molars among species==
<!-- Commented out because image was deleted: [[Image:Tribosphenic.jpg|200px|thumb|Schematic representation of a tribosphenic molar. (A) Upper. (B) Lower.]] -->
Molars differ considerably from one species to another, so there are many terms describing them:
*'''Tribosphenic''': This kind is found in [[insectivore]]s and young [[platypus]]es (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 [[human]]s 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 (tooth)|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 [[mammal]]s. Some paleontologists believe that it developed independently in [[monotreme]]s, rather than being inherited from an ancestor that they share with [[marsupial]]s and [[placental]]s; but this idea has critics and the debate is still going on.<ref>{{ cite journal | author=Stokstad, E. | title=Tooth Theory Revises History of Mammals | journal=Science | date=January 2001 | volume=291 | issie=5501 | pages=26 | doi=10.1126/science.10.1126/SCIENCE.291.5501.26 | url=http://www.sciencemag.org/cgi/content/full/291/5501/26?ck=nck | pmid=11191993}}</ref>
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]]<ref>{{ cite journal | authors=Luo, Z-X., Ji, Q. and Yuan, C-X. | title=Convergent dental adaptations in pseudo-tribosphenic and tribosphenic mammals | journal=Nature | issue=450 | pages=93–97 | date=November 2007 | doi=10.1038/nature06221 | url=http://www.nature.com/nature/journal/v450/n7166/full/nature06221.html | author=Luo, Zhe-Xi | volume=450}}</ref>
==Additional images==
<gallery>
Image:Teeth_molar47_46resection_crown_premolar45.jpg|Molar 47 (left), molar 46 and premolar 45(right)
Image:Illu mouth.jpg|Mouth (oral cavity)
Image:Gray157.png|Left maxilla. Outer surface.
Image:Gray187.png|Base of skull. Inferior surface.
Image:Gray1003.png|The permanent teeth, viewed from the right.
</gallery>
==See also==
*[[Incisor]]
*[[Canine tooth]]
*[[Premolar]]
==References==
{{reflist}}
==External links==
For pictures of various molars see [http://animaldiversity.ummz.umich.edu/anat/tooth_diversity.html The Diversity of Cheek Teeth].
{{Head and neck general}}
[[Category:Teeth]]
[[ca:Queixal]]
[[cs:Stolička]]
[[da:Kindtand]]
[[de:Molar (Zahn)]]
[[es:Molar]]
[[eo:Vangodento#Molaro]]
[[fr:Molaire (dent)]]
[[id:Gigi geraham]]
[[it:Molare]]
[[he:שן טוחנת]]
[[nl:Molaar]]
[[nds-nl:Koeze]]
[[ja:大臼歯]]
[[no:Jeksler]]
[[pl:Ząb trzonowy]]
[[pt:Molar]]
[[simple:Molar]]
[[sr:Кутњаци]]
[[fi:Poskihammas]]
[[sv:Molarer]]
[[te:చర్వణకాలు]]
[[zh:大臼齿]]