Wisdom tooth

A wisdom tooth or third molar 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, but generally occurs between late teens and early twenties. Most adults have four wisdom teeth, one in each of the four quadrants, but it is possible to have none, fewer, or more, 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. While this does not cause movement of other teeth, it can cause tooth decay if the impaction makes oral hygiene difficult. Wisdom teeth which are partially erupted through the gum may also cause inflammation and infection in the surrounding gum tissues, termed pericoronitis. Wisdom teeth are often extracted when or even before these problems occur. However, some, including the National Institute for Health and Care Excellence in the UK, recommend against the prophylactic extraction of disease-free impacted wisdom teeth. Agenesis of wisdom teeth differs by population, ranging from practically zero in Aboriginal Tasmanians to nearly 100% in indigenous Mexicans (see research paper with world map showing prevalence). The difference is related to the PAX9, and MSX1 gene (and perhaps other genes). There is significant variation between the reported age of eruption of wisdom teeth between different populations. For example, wisdom teeth tend to erupt earlier in black people compared to Asian and white people. Generally wisdom teeth are stated as erupting most commonly between age 17 and 21. Eruption may start as early as age 13 in some groups. Sometimes they can erupt up to age 25. If they have not erupted by age 25, oral surgeons generally consider that the tooth will not erupt spontaneously by itself. Wisdom teeth are vestigial third molars that helped human ancestors to grind plant tissue. It is thought that the skulls of human ancestors had larger jaws with more teeth, which possibly helped to chew foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. After the advent of agriculture over 10,000 years ago, soft human diets became the norm, including carbohydrate and high energy foods. Such diets typically result in jaws growing with less forward growth than our paleolithic ancestors and not enough room for the wisdom teeth. Wisdom teeth (often notated clinically as M3 for third molar) have long been identified as a source of problems and continue to be the most commonly impacted teeth in the human mouth. The oldest known impacted wisdom tooth belonged to a European woman of the Magdalenian period (18,000–10,000 BCE). A lack of room to allow the teeth to erupt results in a risk of periodontal disease and dental cavities that increases with age. Less than 2% of adults age 65 years or older maintain the teeth without cavities or periodontal disease and 13% maintain unimpacted wisdom teeth without cavities or periodontal disease. Impacted wisdom teeth are classified by the direction and depth of impaction, the amount of available space for tooth eruption and the amount soft tissue or bone that covers them. The classification structure allows clinicians to estimate the probabilities of impaction, infections and complications associated with wisdom teeth removal. Wisdom teeth are also classified by the presence of symptoms and disease. Treatment of an erupted wisdom tooth is the same as any other tooth in the mouth. If impacted, treatment can be restoration, local treatment to the infected tissue overlying the impaction,:440–441 extraction or coronectomy.