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Chapters

0:00 Introduction
0:35 Causes of Wisdom teeth
2:01 Symptoms of Wisdom teeth
2:31 Treatment for Wisdom teeth



A third molar, commonly called a wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through (erupt) is variable,[1] but this generally occurs between late teens and early twenties.[2] Most adults have four wisdom teeth, one in each of the four quadrants, but it is possible to have none, one to three, or more than four, in which case the extras are called supernumerary teeth.

Wisdom teeth may get stuck (impacted) against other teeth if there is not enough space for them to come through normally,[3] from the jaw being too small, probably because of insufficient chewing of hard and crunchy foods, such as fruits and vegetables, in the years when the bones are still growing.[4] Impacted wisdom teeth are still sometimes removed for orthodontic treatment, believing that they move the other teeth and cause crowding, though this is not held anymore as true.[5] Impacted wisdom teeth may suffer from tooth decay if oral hygiene becomes more difficult. Wisdom teeth which are partially erupted through the gum may also cause inflammation[3] and infection in the surrounding gum tissues, termed pericoronitis. Some more conservative treatments, such as operculectomies, may be fitting for some cases, yet impacted wisdom teeth are commonly extracted as treatment for these problems, many times before these problems even occur. Some institutions and researchers oppose this preventive removal of disease-free impacted wisdom teeth, among them the United Kingdom's National Health Service and National Institute for Health and Care Excellence.[5][6][7] Tooth morphology

Morphology of wisdom teeth can be variable.

Maxillary (upper) third molars commonly have a triangular crown with a deep central fossa from which multiple irregular fissures originate. Their roots are commonly fused together and can be irregular in shape.

Mandibular third molars are the smallest molar teeth in the permanent dentition. The crown usually takes on a rounded rectangular shape that features four or five cusps with an irregular fissure pattern. Roots are greatly reduced in size and can be fused together.[8]
Dental notation

There are several notation systems used in dentistry to identify teeth, including the Palmer/Zsigmondy System. Under the Palmer/Zsigmondy system, the right and left maxillary wisdom teeth are represented by 8┘ and └8, whereas 8┐and ┌8 symbols are used to represent the right and left mandibular wisdom teeth. Another commonly used method of dental notation is the FDI notational system. Under this system, the right and left maxillary third molars are represented by 18 and 28 respectively and the right and left mandibular third molars are numbered as 48 and 38. According to the Universal Numbering System the right and left upper wisdom teeth are labelled 1 and 16 and the right and left lower wisdom teeth are assigned 17 and 32 respectively.
Variation

Agenesis of wisdom teeth differs by population, ranging from practically zero in Aboriginal Tasmanians to nearly 100% in indigenous Mexicans.[9][10] The difference is related to the PAX9, and MSX1 gene (and perhaps other genes).[11][12][13][14]
Age of eruption

There is significant variation between the reported age of eruption of wisdom teeth between different populations.[15] For example, wisdom teeth tend to erupt earlier in people with African heritage compared to Asian and European heritage.[15]

Generally wisdom teeth erupt most commonly between age 17 and 21.[1] Eruption may start as early as age 13 in some groups[15] and typically occurs before the age of 25.[16] If they have not erupted by age 25, oral surgeons generally consider that the tooth will not erupt spontaneously.[2]

Root development can continue for up to three years after eruption occurs.[17]
Clinical significance

Wisdom teeth (often notated clinically as M3 for third molar) are the most commonly impacted teeth in the human mouth.[18] Impacted wisdom teeth lead to pathology in 12% of cases.[19]
Some problems which may or may not occur with third molars: A Mesio-impacted, partially erupted mandibular third molar, B Dental caries and periodontal defects associated with both the third and second molars, caused by food packing and poor access to oral hygiene methods, C Inflamed operculum covering partially erupted lower third molar, with accumulation of food debris and bacteria underneath, D The upper third molar has over-erupted due to lack of opposing tooth contact, and may start to traumatically occlude into the operculum over the lower third molar. Unopposed teeth are usually sharp because they have not been blunted by another tooth.
Dental x-ray of impacted lower left wisdom tooth with a horizontal orientation