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The premolars, also called premolar
teeth A tooth (plural teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth ...
, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per
quadrant Quadrant may refer to: Companies * Quadrant Cycle Company, 1899 manufacturers in Britain of the Quadrant motorcar * Quadrant (motorcycles), one of the earliest British motorcycle manufacturers, established in Birmingham in 1901 * Quadrant Private ...
in the permanent set of teeth, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered transitional teeth during chewing, or
mastication Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, the ...
. They have properties of both the canines, that lay
anterior Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek roots and used to describe something in its standard anatomical position. This position provide ...
and molars that lay
posterior Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to its head ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability, the conditional probability that is assigned when the relevant evidence ...
, 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.


Human anatomy

The premolars in humans are the
maxillary first premolar Maxillary means "related to the maxilla (upper jaw bone)". Terms containing "maxillary" include: *Maxillary artery *Maxillary nerve *Maxillary prominence *Maxillary sinus {{disambig ...
,
maxillary second premolar The maxillary second premolar is one of two teeth located in the upper jaw, laterally (away from the midline of the face) from both the maxillary first premolars of the mouth but mesial (toward the midline of the face) from both maxillary first mola ...
,
mandibular first premolar The mandibular first premolar is the tooth located laterally (away from the midline of the face) from both the mandibular canines of the mouth but mesial (toward the midline of the face) from both mandibular second premolars. The function of this p ...
, and the
mandibular second premolar The mandibular second premolar is the tooth located distally (away from the midline of the face) from both the mandibular first premolars of the mouth but mesial (toward the midline of the face) from both mandibular first molars. The function of th ...
. Premolar teeth by definition are permanent teeth
distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek roots and used to describe something in its standard anatomical position. This position provide ...
to the canines, preceded by
deciduous In the fields of horticulture and botany, the term ''deciduous'' (; ) means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, afte ...
molars.


Morphology

There is always one large buccal cusp, especially so in the mandibular first premolar. The lower second premolar almost always presents with two cusps. 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 In anthropology, Sinodonty and Sundadonty are two patterns of features widely found in the dentitions of different populations in East Asia and Southeast Asia. These two patterns were identified by anthropologist Christy G. Turner II as being with ...
s, and can sometimes have three roots. 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. Whilst the mandibular premolars are rhomboidal in shape.


Maxillary first premolar

* 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

* 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

* 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

* 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 The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two ...
ry first premolars is the second likeliest option, in 14.5% of cases.


Other mammals

In primitive
placental mammal Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mot ...
s there are four premolars per quadrant, but the most
mesial This is a list of definitions of commonly used terms of location and direction in dentistry. This set of terms provides orientation within the oral cavity, much as anatomical terms of location provide orientation throughout the body. Terms ...
two (closer to the front of the mouth) have been lost in
catarrhines The parvorder Catarrhini , catarrhine monkeys or Old World anthropoids are the sister group to the New World monkeys, the Platyrrhini. The Platyrrhini emerged within "monkeys" by migration to South America from Afro-Arabia (the Old World), likely ...
(
Old World monkeys Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae . Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (g ...
and
apes Apes (Hominoidea ) are a branch of Old World tailless simians native to Africa and Southeast Asia. They are the sister group of the Old World monkeys, together forming the catarrhine clade. They are distinguished from other primates by a wider ...
, including humans). Paleontologists therefore refer to human premolars as Pm3 and Pm4.


Additional images


See also

*
Incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas ...


References

{{Authority control Types of teeth