wisdom tooth wisdom tooth a third molar, commonly called 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, but this 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. 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. this article is about the anatomy of wisdom teeth. for wisdom teeth removal surgery, see impacted wisdom teeth. for the 2021 hong kong film, see wisdom tooth (film). wisdom toothwisdom teeth in the human mouth for permanent teeth. there are none in deciduous (children's) teeth.wisdom teethidentifiersmeshd008964ta98a05.1.03.008ta2911fma321612anatomical terminology 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 and infection in the surrounding gum tissues, termed pericoronitis. some more conservative treatments, such as operculectomies, may be appropriate for some cases. yet, impacted wisdom teeth are commonly extracted to treat or prevent these problems. some oppose the prophylactic removal of disease-free impacted wisdom teeth, including the national institute for health and care excellence in the uk. structure main article: human tooth 3d ct of an impacted wisdom tooth near the inferior alveolar nerve 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 (lower) 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. dental notation there are several notation systems used in dentistry to identify teeth. under the palmer/zsigmondy system, the right and left maxillary wisdom teeth are represented by 8┘ and └8, while 8┐and ┌8 represent the right and left mandibular wisdom teeth. under the fdi notational system, the right and left maxillary third molars are numbered 18 and 28, respectively, and the right and left mandibular third molars are numbered 48 and 38. according to the universal numbering system the right and left upper wisdom teeth are numbered 1 and 16 and the right and left lower wisdom teeth are 17 and 32. variation 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). age of eruption 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 people with african heritage compared to people of asian and european heritage. generally wisdom teeth erupt most commonly between age 17 and 21. eruption may start as early as age 13 in some groups and typically occurs before the age of 25. if they have not erupted by age 25, oral surgeons generally consider that the tooth will not erupt spontaneously. root development can continue for up to three years after eruption occurs. function