Thepremolars, also calledpremolarteeth, orbicuspids, are transitional teeth located between thecanine andmolar teeth. In humans, there are two premolars perquadrant in thepermanent set of teeth, making eight premolars total in the mouth.[1][2][3] They have at least twocusps. Premolars can be considered transitional teeth during chewing, ormastication. They have properties of both the canines, that lieanterior and molars that lieposterior, 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]
There is always one largebuccal cusp, especially so in the mandibular first premolar. The lower second premolar almost always presents with twolingual 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 inSinodonts, 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.
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 themaxillary 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 datenot been resolved.[dubious –discuss] 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%.
In primitiveplacental mammals there are four premolars per quadrant, but the mostmesial two (closer to the front of the mouth) have been lost incatarrhines (Old World monkeys andapes, including humans). Paleontologists therefore refer to human premolars as Pm3 and Pm4.[12][13]
^abRoger Warwick; Peter L. Williams, eds. (1973),Gray's Anatomy (35th ed.), London: Longman, pp. 1218–1220
^Weiss, M.L.; Mann, A.E (1985),Human Biology and Behaviour: An anthropological perspective (4th ed.), Boston: Little Brown, pp. 132–135,198–199,ISBN978-0-673-39013-4
