Premolar

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Premolar
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The permanent teeth, viewed from the right
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Permanent teeth of right half of lower dental arch, seen from above
Details
Identifiers
Latin dentes premolares
MeSH D001641
TA98 A05.1.03.006
TA2 909
FMA 55637
Anatomical terminology

The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth. [1] [2] [3] They have at least two 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, 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. [4]

Contents

Human anatomy

The premolars in humans are the maxillary first premolar, maxillary second premolar, mandibular first premolar, and the mandibular second premolar. [1] [3] Premolar teeth by definition are permanent teeth distal to the canines, preceded by deciduous molars. [5]

Morphology

There is always one large buccal cusp, especially so in the mandibular first premolar. The lower second premolar almost always presents with two lingual cusps. [6]

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 Sinodonts, and can sometimes have three roots. [7] [8]

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 [9]

  • 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 [9]

  • 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 [9]

  • 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 [9]

  • 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 maxillary first premolars is the second likeliest option, in 14.5% of cases. [10] 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. [11] The debate has to date not been resolved. [ dubious ] 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 placental mammals there are four premolars per quadrant, but the most mesial two (closer to the front of the mouth) have been lost in catarrhines (Old World monkeys and apes, including humans). Paleontologists therefore refer to human premolars as Pm3 and Pm4. [12] [13]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Canine tooth</span> Long pointed tooth in mammals

In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as fangs. They can appear more flattened however, causing them to resemble incisors and leading them to be called incisiform. They developed and are used primarily for firmly holding food in order to tear it apart, and occasionally as weapons. They are often the largest teeth in a mammal's mouth. Individuals of most species that develop them normally have four, two in the upper jaw and two in the lower, separated within each jaw by incisors; humans and dogs are examples. In most species, canines are the anterior-most teeth in the maxillary bone. The four canines in humans are the two upper maxillary canines and the two lower mandibular canines. They are specially prominent in dogs (canidae), hence the name.

<span class="mw-page-title-main">Maxillary central incisor</span> Tooth

The maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication (chewing). There is typically a single cusp on each tooth, called an incisal ridge or incisal edge. Formation of these teeth begins at 14 weeks in utero for the deciduous (baby) set and 3–4 months of age for the permanent set.

<span class="mw-page-title-main">Maxillary first molar</span>

The maxillary first molar is the human tooth located laterally from both the maxillary second premolars of the mouth but mesial from both maxillary second molars.

<span class="mw-page-title-main">Mandibular canine</span>

The mandibular canine is the tooth located distally from both mandibular lateral incisors of the mouth but mesially from both mandibular first premolars. Both the maxillary and mandibular canines are called the "cornerstone" of the mouth because they are all located three teeth away from the midline, and separate the premolars from the incisors. The location of the canines reflect their dual function as they complement both the premolars and incisors during mastication, commonly known as chewing. Nonetheless, the most common action of the canines is tearing of food. The canine teeth are able to withstand the tremendous lateral pressures from chewing. There is a single cusp on canines, and they resemble the prehensile teeth found in carnivorous animals. Though relatively the same, there are some minor differences between the deciduous (baby) mandibular canine and that of the permanent mandibular canine.

<span class="mw-page-title-main">Mandibular first premolar</span>

The mandibular first premolar is the tooth located laterally from both the mandibular canines of the mouth but mesial from both mandibular second premolars. The function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication, commonly known as chewing. Mandibular first premolars have two cusps. The one large and sharp is located on the buccal side of the tooth. Since the lingual cusp is small and nonfunctional, the mandibular first premolar resembles a small canine. There are no deciduous (baby) mandibular premolars. Instead, the teeth that precede the permanent mandibular premolars are the deciduous mandibular molars.

<span class="mw-page-title-main">Mandibular second premolar</span>

The mandibular second premolar is the tooth located distally from both the mandibular first premolars of the mouth but mesial from both mandibular first molars. The function of this premolar is assist the mandibular first molar during mastication, commonly known as chewing. Mandibular second premolars have three cusps. There is one large cusp on the buccal side of the tooth. The lingual cusps are well developed and functional. Therefore, whereas the mandibular first premolar resembles a small canine, the mandibular second premolar is more alike to the first molar. There are no deciduous (baby) mandibular premolars. Instead, the teeth that precede the permanent mandibular premolars are the deciduous mandibular molars.

<span class="mw-page-title-main">Mandibular first molar</span>

The mandibular first molar or six-year molar is the tooth located distally from both the mandibular second premolars of the mouth but mesial from both mandibular second molars. It is located on the mandibular (lower) arch of the mouth, and generally opposes the maxillary (upper) first molars and the maxillary 2nd premolar in normal class I occlusion. The function of this molar is similar to that of all molars in regard to grinding being the principal action during mastication, commonly known as chewing. There are usually five well-developed cusps on mandibular first molars: two on the buccal, two lingual, and one distal. The shape of the developmental and supplementary grooves, on the occlusal surface, are described as being 'M' shaped. There are great differences between the deciduous (baby) mandibular molars and those of the permanent mandibular molars, even though their function are similar. The permanent mandibular molars are not considered to have any teeth that precede it. Despite being named molars, the deciduous molars are followed by permanent premolars.

Dens evaginatus is a rare odontogenic developmental anomaly that is found in teeth where the outer surface appears to form an extra bump or cusp.

Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development, appearance, and classification of teeth fall within its purview. Tooth formation begins before birth, and the teeth's eventual morphology is dictated during this time. Dental anatomy is also a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment.

Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest.

<span class="mw-page-title-main">Cusp (anatomy)</span> Pointed, projecting, or elevated anatomical feature

A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth. The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has two cusps, is also known as the bicuspid valve, and the tricuspid valve has three cusps.

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.

<span class="mw-page-title-main">Crossbite</span> Medical condition

Crossbite is a form of malocclusion where a tooth has a more buccal or lingual position than its corresponding antagonist tooth in the upper or lower dental arch. In other words, crossbite is a lateral misalignment of the dental arches.

Dental pertains to the teeth, including dentistry. Topics related to the dentistry, the human mouth and teeth include:

<span class="mw-page-title-main">Lingual arch</span>

A lingual arch is an orthodontic device which connects two molars in the upper or lower dental arch. The lower lingual arch (LLA) has an archwire adapted to the lingual side of the lower teeth. In the upper arch the archwire is usually connecting the two molars passing through the palatal vault, and is commonly referred as "Transpalatal Arch" (TPA). The TPA was originally described by Robert Goshgarian in 1972. TPAs could possibly be used for maintaining transverse arch widths, anchorage in extraction case, prevent buccal tipping of molars during Burstonian segmented arch mechanics, transverse anchorage and space maintenance.

<span class="mw-page-title-main">Lewis offset</span>

The Lewis offset is a term for the portion of the central groove on a permanent mandibular first molar which lies between the two central pits. It was named for long time dental anatomy instructor Dr. Christopher S. Lewis, a Mercer Island, WA dentist.

Serial extraction is the planned extraction of certain deciduous teeth and specific permanent teeth in an orderly sequence and predetermined pattern to guide the erupting permanent teeth into a more favorable position.

Intrusion is a movement in the field of orthodontics where a tooth is moved partially into the bone. Intrusion is done in orthodontics to correct an anterior deep bite or in some cases intrusion of the over-erupted posterior teeth with no opposing tooth. Intrusion can be done in many ways and consists of many different types. Intrusion, in orthodontic history, was initially defined as problematic in early 1900s and was known to cause periodontal effects such as root resorption and recession. However, in mid 1950s successful intrusion with light continuous forces was demonstrated. Charles J. Burstone defined intrusion to be "the apical movement of the geometric center of the root (centroid) in respect to the occlusal plane or plane based on the long axis of tooth".

An ectopic maxillary canine is a canine which is following abnormal path of eruption in the maxilla. An impacted tooth is one which is blocked from erupting by a physical barrier in the path of eruption. Ectopic eruption may lead to impaction. Previously, it was assumed that 85% of ectopic canines are displaced palatally, however a recent study suggests the true occurrence is closer to 50%. While maxillary canines can also be displaced buccally, it is thought this arises as a result of a lack of space. Most of these cases resolve themselves with the permanent canine erupting without intervention.

Orthodontic indices are one of the tools that are available for orthodontists to grade and assess malocclusion. Orthodontic indices can be useful for an epidemiologist to analyse prevalence and severity of malocclusion in any population.

References

  1. 1 2 Roger Warwick; Peter L. Williams, eds. (1973), Gray's Anatomy (35th ed.), London: Longman, pp. 1218–1220
  2. Weiss, M.L.; Mann, A.E (1985), Human Biology and Behaviour: An anthropological perspective (4th ed.), Boston: Little Brown, pp. 132–135, 198–199, ISBN   978-0-673-39013-4
  3. 1 2 Glanze, W.D.; Anderson, K.N.; Anderson, L.E, eds. (1990), Mosby's Medical, Nursing & Allied Health Dictionary (3rd ed.), St. Louis, Missouri: The C.V. Mosby Co., p. 957, ISBN   978-0-8016-3227-3
  4. Weiss, M.L., & Mann, A.E. (1985), pp.132-134
  5. Warwick, R., & Williams, P.L. (1973), pp.1218-1219.
  6. Warwick, R., & Williams, P.L. (1973), p.1219.
  7. Standring, Susan (2015). Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences. p. 518. ISBN   9780702068515.
  8. Kimura, Ryosuke; Yamaguchi, Tetsutaro; Takeda, Mayako; Kondo, Osamu; Toma, Takashi; Haneji, Kuniaki; Hanihara, Tsunehiko; Matsukusa, Hirotaka; Kawamura, Shoji; Maki, Koutaro; Osawa, Motoki; Ishida, Hajime; Oota, Hiroki (2009). "A Common Variation in EDAR is a Genetic Determinant of Shovel-Shaped Incisors". The American Journal of Human Genetics. 85 (4): 528–535. doi:10.1016/j.ajhg.2009.09.006. PMC   2756549 . PMID   19804850.
  9. 1 2 3 4 Berkovitz, B. K. B. (2009). Oral anatomy, histology and embryology. G. R. Holland, B. J. Moxham (4th ed.). Edinburgh: Mosby/Elsevier. ISBN   978-0-7234-3583-9. OCLC   806280585.
  10. Capelli Júnior, Jonas; Fernandes, Luciana Q. P.; Dardengo, Camila de S.; Capelli Júnior, Jonas; Fernandes, Luciana Q. P.; Dardengo, Camila de S. (2016). "Frequency of orthodontic extraction". Dental Press Journal of Orthodontics. 21 (1): 54–59. doi:10.1590/2177-6709.21.1.054-059.oar. ISSN   2176-9451. PMC   4816586 . PMID   27007762.
  11. Sun, FC (2018). "Effect of incisor retraction on three-dimensional morphology of upper airway and fluid dynamics in adult class I patients with bimaxillary protrusion". Zhonghua Kou Qiang Yi Xue Za Zhi. 53 (6): 398–403. doi:10.3760/cma.j.issn.1002-0098.2018.06.007. PMID   29886634 . Retrieved 2 May 2022.
  12. Christopher Dean (1994). "Jaws and teeth". In Steve Jones; Robert Martin; David Pilbeam (eds.). The Cambridge Encyclopedia of Human Evolution. Cambridge: Cambridge University Press. pp.  56–59. ISBN   978-0-521-32370-3. Also ISBN   0-521-46786-1 (paperback)
  13. Gentry Steele and Claud Bramblett (1988). The Anatomy and Biology of the Human Skeleton . Texas A&M University Press. p.  82. ISBN   9780890963265.