Wisdom tooth

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This article deals with the anatomy of wisdom teeth. For wisdom teeth removal surgery see: Impacted wisdom teeth
Wisdom tooth
Weisheitszähne-1.jpg
Wisdom teeth
3D CT impacted wisdom tooth.Gif
Identifiers
TA A05.1.03.008
Anatomical terminology

A wisdom tooth or third molar is one of the three molars per quadrant of the human dentition. It is the most posterior (most distal) of the three. Wisdom teeth generally appear between the ages of 17 and 25.[1] Most adults have four wisdom teeth (a third molar in each of the four quadrants), but it is possible to have fewer or more, in which case the extras are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or "coming in sideways." They are often extracted when this occurs.

Anatomy[edit]

Main article: Human tooth

Variation[edit]

Agenesis of wisdom teeth differs by population, ranging from practically zero in Tasmanian Aborigines to nearly 100% in indigenous Mexicans.[2] The difference is related to the PAX9 gene (and perhaps other genes).[3]

Function[edit]

Wisdom teeth are vestigial third molars that used to help human ancestors in grinding down plant tissue. The common postulation is that the skulls of human ancestors had larger jaws with more teeth, which were possibly used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. As human diets changed, smaller jaws gradually evolved, yet the third molars, or "wisdom teeth", still commonly develop in human mouths.[4]

Wisdom teeth may have another function that has been researched in recent years, to be used as stem cells. The stem cells inside of a wisdom tooth recently removed from a patients mouth can be extracted and saved for a later use in brain cells, nerve cells, or to even grow another tooth.[5]

Clinical significance[edit]

A wisdom tooth protrudes outwards from the gumline with inflamed tissue at the back (pericoronitis; green arrow)

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 BC).[6] A lack of room to allow the teeth to erupt results in a risk of periodontal disease and caries that increases with age.[7] Only a small minority (less than 2%) of adults age 65 years or older maintain the teeth without caries or periodontal disease and 13% maintain unimpacted wisdom teeth without caries or periodontal disease.[8]

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 (attrition).

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 (or both) that covers them. The classification structure allows clinicians to estimate the probabilities of impaction, infections and complications associated with wisdom teeth removal.[7] Wisdom teeth are also classified by the presence (or absence) of symptoms and disease.[9]

Treatment of an erupted wisdom tooth is the same as any other tooth in the mouth. If impacted, treatment can be localized to the infected tissue overlying the impaction,[10]:440–441 extraction[11] or coronectomy.[12]

The upper left (picture right) and upper right (picture left) wisdom teeth are distoangularly impacted. The lower left wisdom tooth is horizontally impacted. The lower right wisdom tooth is vertically impacted (unidentifiable in orthopantomogram).

History[edit]

Although formally known as third molars, the common name is wisdom teeth because they appear so late – much later than the other teeth, at an age where people are presumably "wiser" than as a child, when the other teeth erupt.[13] The term probably came as a translation of the Latin: dens sapientiae.

Wisdom Teeth and Stem Cells[edit]

Although it seems that wisdom teeth serve no purpose to modern day Homo sapiens, they could actually be the root of a new scientific revolution. Lately, there has been a lot of interest in stem cells because they can act as blank slates and help cure diseases or simply grow into which ever cells are needed.[14] In 2006 scientists revealed that the cells in wisdom teeth can be used as stem cells and even kept frozen for later use in life.[15] Since stem cells are a controversial topic due to the ways they need to obtain them this would be a great finding for the medical community. Considering almost every present day Homo sapiens get their wisdom teeth removed in their lifetime, they each have access to stem cells if they ever need them. This means that if a person contracts cancer or something happens to an organ they could have a supply of stem cells to their disposal. Though, third molars used to aid the ancestors of Homo sapiens as a necessity in terms of every day survival, they now have the power to aid modern day Homo sapiens in a different way. The stem cells can be another way to attempt and fight off an otherwise terminal disease or illness. Though they did not originally evolve for this purpose and had a different underlying advantage they can actually be very beneficial to their present day host. Even though wisdom teeth are no longer a necessity to the survival of Homo sapiens they have not been selected against. One reason that they may not be readily selected against is because modern Homo sapiens’ access to removal eliminates the selective pressures that are acting on the wisdom teeth.

See also[edit]

This article uses anatomical terminology; for an overview, see anatomical terminology.

References[edit]

  1. ^ "Wisdom Teeth". American Association of Oral and Maxillofacial Surgeons. Retrieved 2010-09-28. "This generally occurs between the ages of 17 and 25" 
  2. ^ Rozkovcová, E; Marková, M; Dolejsí, J (1999). "Studies on agenesis of third molars amongst populations of different origin". Sbornik lekarsky 100 (2): 71–84. PMID 11220165. 
  3. ^ Pereira, Tiago V.; Salzano, Francisco M.; Mostowska, Adrianna; Trzeciak, Wieslaw H.; Ruiz-Linares, Andrés; Chies, José A. B.; Saavedra, Carmen; Nagamachi, Cleusa et al. (2006). "Natural selection and molecular evolution in primate PAX9 gene, a major determinant of tooth development". Proceedings of the National Academy of Sciences 103 (15): 5676–81. Bibcode:2006PNAS..103.5676P. doi:10.1073/pnas.0509562103. JSTOR 30050159. PMC 1458632. PMID 16585527. 
  4. ^ Johnson, Dr. George B. "Evidence for Evolution". (Page 12) Txtwriter Inc. 8 Jun 2006.[self-published source?]
  5. ^ University of Adelaide. "Stem cells from teeth can make brain-like cells." ScienceDaily. ScienceDaily, 30 April 2014. <www.sciencedaily.com/releases/2014/04/140430192527.htm>.
  6. ^ "Magdalenian Girl is a woman and therefore has oldest recorded case of impacted wisdom teeth" (Press release). Field Museum of Natural History. March 7, 2006. Retrieved February 15, 2013. 
  7. ^ a b Juodzbalys, Gintaras; Daugela, Povilas (Apr–Jun 2013). "Mandibular Third Molar Impaction: Review of Literature and a Proposal of a Classification (review)". J Oral Maxillofac Res 4 (2): e1. doi:10.5037/jomr.2013.4201. PMC 3886113. PMID 24422029.  Missing |last1= in Authors list (help)
  8. ^ Marciani RD (2012). "Is there pathology associated with asymptomatic third molars (review)". J Oral Maxillofac Surg 70 (Suppl 1): 15–19. doi:10.1016/j.joms.2012.04.025. 
  9. ^ Dodson TB (Sep 2012). "The management of the asymptomatic, disease-free wisdom tooth: removal versus retention. (review)". Atlas Oral Maxillofac Surg clin North Am 20 (2): 169–76. doi:10.1016/j.cxom.2012.06.005. PMID 23021394. 
  10. ^ Newman MG, Takei HH, Klokkevold PR, Carranza FA (2012). Carranza's Clinical Periodontology. Elsevier Saunders. ISBN 978-1-4377-0416-7. 
  11. ^ Pogrel MA (2012). "What are the Risks of Operative Intervention (review)". J Oral Maxillofac Surg 70 (Suppl 1): 33–36. 
  12. ^ Ghaeminia H (2013). "Coronectomy may be a way of managing impacted third molars (systematic review)". Evid Based Dent 14 (2): 57–8. doi:10.1038/sj.ebd.6400939. PMID 23792405. 
  13. ^ "Wisdom tooth". Oxford English Dictionary. Oxford: Oxford University Press. 1989. ISBN 0-19-861186-2. 
  14. ^ (Dybas, 2007)
  15. ^ (Shere, 2010)

External links[edit]