View source for Premolar

{{Short description|Transitional teeth located between the canine and molar teeth}}
{{Infobox anatomy
| Name      = Premolar
| Latin     = [[dentes premolares]]
| Greek     =
| Image     = Gray1003.png
| Caption   = The permanent teeth, viewed from the right
| Width     =
| Image2    = Gray997.png
| Caption2  = Permanent teeth of right half of lower dental arch, seen from above
| Precursor =
| System    =
| Artery    =
| Vein      =
| Nerve     =
| Lymph     =
}}
The '''premolars''', also called '''premolar''' [[Tooth (human)|teeth]], or '''bicuspids''', are transitional teeth located between the [[Canine tooth|canine]] and [[Molar (tooth)|molar]] teeth. In humans, there are two premolars per [[dental terminology#Quadrant|quadrant]] in the [[permanent teeth|permanent]] set of teeth, making eight premolars total in the mouth.<ref name="GraysAnatomy35thBritish" /><ref name="Weiss&Mann1985" /><ref name="MosbysDictionary3rded" />  They have at least two [[Cusp (dentistry)|cusps]].  Premolars can be considered transitional teeth during chewing, or [[mastication]]. They have properties of both the canines, that lie [[anterior]] and molars that lie [[Posterior (anatomy)|posterior]], and so food can be transferred from the canines to the premolars and finally to the molars for grinding, instead of directly from the canines to the molars.<ref name="Weiss&Mann1985pp132-134" />

== Human anatomy ==
The premolars in humans are the [[maxillary first premolar]], [[maxillary second premolar]], [[mandibular first premolar]], and the [[mandibular second premolar]].<ref name="GraysAnatomy35thBritish" /><ref name="MosbysDictionary3rded" /> Premolar teeth by definition are permanent teeth [[Anatomical terms of location#Proximal and distal|distal]] to the canines, preceded by [[deciduous teeth|deciduous]] molars.<ref name="GraysAnatomy35thBritishpp1218-1219" />

=== Morphology ===
There is always one large [[cheek|buccal]] cusp, especially so in the mandibular first premolar. The lower second premolar almost always presents with two [[tongue|lingual]] cusps.<ref name="GraysAnatomy35thBritishp1219" />

The lower premolars and the upper second premolar usually have one root. The upper first usually has two roots, but can have just one root, notably in [[Sinodont]]s, and can sometimes have three roots.<ref name="Grays-ebook">{{cite book|last1=Standring|first1=Susan|title=Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice|date=2015|publisher=Elsevier Health Sciences|isbn=9780702068515|page=518|url=https://books.google.com/books?id=b7FVCgAAQBAJ&pg=PA518|language=en}}</ref><ref name="Kimura">{{Cite journal | doi=10.1016/j.ajhg.2009.09.006| pmid=19804850| pmc=2756549| title=A Common Variation in EDAR is a Genetic Determinant of Shovel-Shaped Incisors| journal=The American Journal of Human Genetics| volume=85| issue=4| pages=528–535| year=2009| last1=Kimura| first1=Ryosuke| last2=Yamaguchi| first2=Tetsutaro| last3=Takeda| first3=Mayako| last4=Kondo| first4=Osamu| last5=Toma| first5=Takashi| last6=Haneji| first6=Kuniaki| last7=Hanihara| first7=Tsunehiko| last8=Matsukusa| first8=Hirotaka| last9=Kawamura| first9=Shoji| last10=Maki| first10=Koutaro| last11=Osawa| first11=Motoki| last12=Ishida| first12=Hajime| last13=Oota| first13=Hiroki}}</ref>

Premolars are unique to the permanent dentition. Premolars are referred to as bicuspid (has two main cusps), a buccal and a palatal/lingual cusp which are separated by a mesiodistal occlusal fissure.

The maxillary premolars are trapezoidal in shape, while the mandibular premolars are rhomboidal in shape.

==== Maxillary first premolar ====
Source:<ref name=":0">{{Cite book|last=Berkovitz|first=B. K. B.|title=Oral anatomy, histology and embryology|date=2009|publisher=Mosby/Elsevier|others=G. R. Holland, B. J. Moxham|isbn=978-0-7234-3583-9|edition=4th|location=Edinburgh|oclc=806280585}}</ref>
* The crown of the tooth appears ovoid, wider buccally than palatally
* From a buccal view, the first premolar is similar to the adjacent canine
* Roots: Two roots buccal and palatal. Sometimes (40%) there is only one root.

==== Maxillary second premolar ====
Source:<ref name=":0" />
* Similar to maxillary first premolar but the mesio-buccal and disto-buccal corners are rounder
* The two cusps are smaller and more equal in size
* Shorter occlusal fissure
* Usually one root

==== Mandibular first premolar ====
Source:<ref name=":0" />
* The smallest premolar out of all four
* Dominant buccal cusp and a very small lingual cusp 
* The buccal cusp is broad and the lingual cusp is less than half the size of the buccal cusp.
* Two-thirds of the buccal surface can be seen from the occlusal aspect
* A single conical root with an oval/round cross section. The root is grooved longitudinally both mesially and distally.

==== Mandibular second premolar ====
Source:<ref name=":0" />
* The crown is larger than the mandibular first premolar
* Lingual cusp is smaller than the buccal cusp but better developed. 
* The lingual and buccal cusp is separated by a well defined mesiodistal occlusal fissure
* The lingual cusp is divided into two; the mesiolingual and distolingual cusps with the mesiolingual cusp being higher and wider than the distolingual. 
* Root: Single conical root, oval/round in cross section.

== Orthodontics ==
The four first premolars are the most commonly removed teeth, in 48.8% of cases, when teeth are removed for orthodontic treatment (which is in 45.8% of orthodontic patients). The removal of only the [[maxilla]]ry first premolars is the second likeliest option, in 14.5% of cases.<ref>{{Cite journal|last1=Capelli Júnior|first1=Jonas|last2=Fernandes|first2=Luciana Q. P.|last3=Dardengo|first3=Camila de S.|last4=Capelli Júnior|first4=Jonas|last5=Fernandes|first5=Luciana Q. P.|last6=Dardengo|first6=Camila de S.|title=Frequency of orthodontic extraction|journal=Dental Press Journal of Orthodontics|language=en|volume=21|issue=1|pages=54–59|doi=10.1590/2177-6709.21.1.054-059.oar|pmid=27007762|issn=2176-9451|date=2016|pmc=4816586}}</ref>  The practice of premolar extraction developed in the 1940s in the United States, and was initially greatly contested in the orthodontic field, due to the changes to the facial structure caused by the retraction of the arches.  Known as "the Great Controversy in Orthodontics," the debate over extractions was revived in the 1990s, following numerous patient reports of health consequences due to extraction/retraction, from TMD to Obstructive Sleep Apnea, and published research on the reduction of the pharyngeal airway due to the retraction.<ref>{{cite journal |last1=Sun |first1=FC |title=Effect of incisor retraction on three-dimensional morphology of upper airway and fluid dynamics in adult class I patients with bimaxillary protrusion |journal=Zhonghua Kou Qiang Yi Xue Za Zhi |year=2018 |volume=53 |issue=6  |pages=398–403 |doi=10.3760/cma.j.issn.1002-0098.2018.06.007 |pmid=29886634 }}</ref>  The debate has to date [https://karinbadt.medium.com/premolar-extractions-for-orthodontic-treatment-2190344bc7bf not been resolved.]{{Dubious|date=August 2023}} Today more and more orthodontists are avoiding the use of what is termed 'extraction therapy,' and in the United States, the official rate is now 25%.

== Other mammals ==
In primitive [[Eutheria|placental mammal]]s there are four premolars per quadrant, but the most [[mesial]] two (closer to the front of the mouth) have been lost in [[catarrhines]] ([[Cercopithecoidea|Old World monkeys]] and [[Hominoidea|apes]], including humans). Paleontologists therefore refer to human premolars as Pm3 and Pm4.<ref name="encylopediahumanevolution" /><ref>{{cite book|last1=[[Gentry Steele]] and [[Claud Bramblett]]|title=The Anatomy and Biology of the Human Skeleton|publisher=Texas A&M University Press|date=1988|isbn=9780890963265|page=[https://archive.org/details/anatomybiologyo00stee/page/82 82]|url=https://archive.org/details/anatomybiologyo00stee|url-access=registration}}</ref>

== Additional images ==
{{Gallery
|File: 3D Medical Animation Still Showing Types of Teeth.jpg|Medical animation showing Premolar teeth and its arrangement in the mouth of an adult human being
|File:Illu mouth.jpg|Mouth (oral cavity)|File:Gray157.png|Left maxilla, outer surface
|File:Gray187.png|Base of skull, interior surface
}}

== See also ==
{{Portal|Medicine}}
* [[Incisor]]

== References ==
{{Reflist|refs=
<ref name="GraysAnatomy35thBritish">{{citation| title=Gray's Anatomy |editor1=Roger Warwick |editor2=Peter L. Williams | edition=35th | publisher= Longman |location=London|year=1973|pages=1218–1220}}</ref>

<ref name="GraysAnatomy35thBritishp1219">Warwick, R., & Williams, P.L. (1973), p.1219.</ref>

<ref name="GraysAnatomy35thBritishpp1218-1219">Warwick, R., & Williams, P.L. (1973), pp.1218-1219.</ref>

<ref name="encylopediahumanevolution">{{cite book | title=The Cambridge Encyclopedia of Human Evolution | author=Christopher Dean | chapter=Jaws and teeth |editor1=[[Steve Jones (biologist)|Steve Jones]] |editor2=Robert Martin |editor3=[[David Pilbeam]] | year=1994 | publisher=Cambridge University Press | location=Cambridge | isbn=978-0-521-32370-3 | pages=[https://archive.org/details/cambridgeencyclo00step/page/56 56–59] | chapter-url=https://archive.org/details/cambridgeencyclo00step/page/56 }} Also {{ISBN|0-521-46786-1}} (paperback)</ref>

<ref name="MosbysDictionary3rded">{{citation| title=Mosby's Medical, Nursing & Allied Health Dictionary |editor1=Glanze, W.D. |editor2=Anderson, K.N. |editor3=Anderson, L.E | edition=3rd | publisher= The C.V. Mosby Co.|location=St. Louis, Missouri |year=1990 |isbn=978-0-8016-3227-3|page=957| title-link=Mosby's Medical, Nursing & Allied Health Dictionary }}</ref>

<ref name="Weiss&Mann1985">{{citation|year=1985 |author1=Weiss, M.L. |author2=Mann, A.E |title=Human Biology and Behaviour: An anthropological perspective |edition=4th |place=Boston |publisher= Little Brown |pages=132–135, 198–199 |isbn=978-0-673-39013-4}}</ref>

<ref name="Weiss&Mann1985pp132-134">Weiss, M.L., & Mann, A.E. (1985), pp.132-134</ref>

}}

{{Tooth anatomy}}
{{Authority control}}

[[Category:Types of teeth]]