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.
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:
- 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: 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. The debate has to date not been resolved. 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.
Additional images
See also
- Incisor