Wisdom teeth and genetics: Why some people do not have wisdom teeth

Did you know that wisdom teeth are actually an evolutionary leftover from our ancient ancestors that no longer serve their original purpose? These molars were once necessary to grind up tough, uncooked foods like roots, nuts, and raw meats, but as humans evolved and developed a softer diet, our jaws became smaller and no longer needed or had room for these extra teeth. However, some people still have them.

Maybe you have a third set of molars, called third molars and otherwise known as wisdom teeth, or maybe you don’t. Perhaps you have had your wisdom teeth removed or you know someone who has, but have you ever wondered why not everyone needs to go through this, or why not everyone has wisdom teeth? It may not surprise you to hear that the presence or absence of wisdom teeth is influenced by your genetics.

Why are third molars called wisdom teeth?

Wisdom teeth usually come through in the late teens or early adulthood. In comparison to the age when other teeth come through, someone at this stage of life is generally considered “older and wiser”, hence the name: wisdom teeth.

Not everyone has wisdom teeth and some people may not have all four. It is also possible that they will not come through in everyone who has them, and these people may only become aware of their presence after a dental x-ray.

Why do we have wisdom teeth? Do we need them?

It is thought that extra molars were necessary for our ancient ancestors due to a diet that included tough, raw meat and plants and their lack of dental hygiene. However, as humans evolved and our diets changed, the human jaw became smaller and no longer had sufficient space for all the teeth. In modern terms, this lack of space means that wisdom teeth often need removing. Removal is also necessary if the teeth are impacted, meaning their eruption is prevented by the angle of the tooth or the location of other teeth [1].

Luckily, we do not need wisdom teeth for eating, so those people who have them removed or simply do not have them are not at a disadvantage.

Geographical differences in wisdom teeth prevalence

The prevalence of third molar agenesis (the absence of wisdom teeth) appears to show geographical differences; however, interpreting the data is complicated as agenesis includes the absence of one or more of the wisdom teeth. One study of third molar agenesis in Bangladeshi patients that included a review summary of other populations, showed that the prevalence of third molar agenesis in the Bangladeshi population was relatively high (38.4%) in comparison to other countries (e.g., India 11.5%) but not as high as among Koreans (41%). However, sample size differences must be noted [2]. Elsewhere, it has been reported that 100% of indigenous Mexicans have third molar agenesis [3].  A more recent review study reported that the worldwide rate of third molar agenesis is 22.63%, with estimates in the analysis ranging from 5.32% to 56.0%. They noted geographical differences and reported that women were more likely to have at least one missing wisdom tooth than men were [4].

The variations are perhaps most clearly illustrated by prevalence data for North America. It has been estimated that 10-25% of Americans with European ancestry, 11% of African Americans and 40% of Asian Americans are missing at least one wisdom tooth. While 45% of Inuit, indigenous people who live in the arctic regions of Canada, Alaska and Greenland, have at least one missing wisdom tooth [5].

Why do not all people have wisdom teeth?

Scientists know that both genetics and environmental factors affect the development of wisdom teeth.

Genetics and wisdom teeth

As mentioned above, evolution has encouraged the absence of wisdom teeth. Human brain evolution resulted in a larger skull and smaller jaw with less space for all the teeth, cooking methods also evolved so that overall there was less biological need for third molars. It has also been suggested that the pain felt by our ancestors with impacted wisdom teeth (due to smaller jaws) meant they were less likely to reproduce. As a result, natural selection favored those without wisdom teeth [5]. 

Researchers have discovered that changes in genes affecting teeth development occur independently of brain evolution; nevertheless, there were mutations (genetic variants) that occurred thousands of years ago that prevented the formation of wisdom teeth. These variants were favorable due to man’s smaller jaw and positive selection meant they became more widespread [5].

Furthermore, research suggests that the absence of wisdom teeth is heritable. A study of 284 same‑sex twins investigating third molar agenesis, found that monozygotic (identical) twins had a slightly higher prevalence of third molar agenesis than dizygotic twins did. The authors reported that agenesis of third molars was associated with additive genetic factors that accounted for approximately 60-80% of the variation seen in the study, with the environment accounting for the remainder of the variation [6].

It is thought that around 80% of non-syndromic tooth agenesis is caused by changes in genes involved in facial and tooth development, including the genes AXIN2, MSX1 and PAX9 [7]. However, studies of dental agenesis often exclude the third molars; therefore, the exact genetic cause of wisdom teeth agenesis is unclear. Despite this, polymorphisms in the PAX9 gene have been linked to third molar agenesis in a small number of cases [8, 9], although not all studies have found an association [10]. A study in Japanese and Korean subjects reported an association between third molar agenesis and a single nucleotide polymorphism in the gene THSD7B [11].

The relationship between third molar agenesis and agenesis of other teeth is also interesting; one study of European subjects reported that third molar agenesis was more common where there was agenesis of other teeth. The authors concluded that third molars might be vulnerable to genetic factors that affect the overall number of teeth and suggested this indicates continued human evolution towards fewer teeth [12].

Genetic factors also account for variations in the rate of root mineralization of wisdom teeth [13].

What other factors influence the development of wisdom teeth?

Exposure to chemotherapy, certain viruses and various medications at a young age can affect the development of permanent teeth [7]. In fact, researchers have found that children receiving local anesthesia injections in the gums between the ages of 2 and 6 years were more likely not to develop wisdom teeth than other children [14].

There are patterns of wisdom tooth prevalence in certain ethnic populations, and it is possible that specific ethnic differences are caused by local environmental factors or lifestyles.

The future of wisdom teeth

It has been suggested that the positive selection of genetic variants for third molar agenesis is reduced in developed nations due to modern dental practices [15]; however, it is still possible that eventually, third molar agenesis will be even more common and wisdom teeth will no longer exist.

Conclusion

Wisdom teeth, also known as third molars, usually come through in the late teenage years or in early adulthood. Their diet meant these teeth were necessary for our ancient ancestors, but today they are no longer necessary for eating and many people are missing one or more third molar. The trend towards fewer or absent wisdom teeth has been driven by human evolution, with genetics and environmental factors affecting wisdom tooth prevalence.

References

[1] Healthline. Wisdom Teeth. Retrieved 8 February 2023 from https://www.healthline.com/health/why-do-we-have-wisdom-teeth#when-do-wisdom-teeth-come-in

[2] Sujon MK et al. Prevalence of Third Molar Agenesis: Associated Dental Anomalies in Non-Syndromic 5923 Patients. PLOS ONE 2016;11(8): e0162070. https://doi.org/10.1371/journal.pone.0162070

[3] Rozkovcová E et al. Studies on agenesis of third molars amongst populations of different origin. Sb Lek 1999;100(2):71-84. PMID: 11220165. https://pubmed.ncbi.nlm.nih.gov/11220165/

[4] Carter K, Worthington S. Morphologic and Demographic Predictors of Third Molar Agenesis: A Systematic Review and Meta-analysis. J Dent Res 2015;94(7):886-94. doi: 10.1177/0022034515581644. Epub 2015 Apr 16. PMID: 25883107. https://pubmed.ncbi.nlm.nih.gov/25883107/

[5] Main D. 13 March 2013. Ancient Mutation Explains Missing Wisdom Teeth. Live Science. Retrieved 8 February 2023 from https://www.livescience.com/27529-missing-wisdom-teeth.html

[6] Trakinienė G et al. Impact of genetics on third molar agenesis. Sci Rep 2018;8:8307. https://doi.org/10.1038/s41598-018-26740-7 https://www.nature.com/articles/s41598-018-26740-7.pdf

[7] Letra A et al. Nonsyndromic Tooth Agenesis Overview. 2021 Jul 22. In: Adam MP, Everman DB, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572295/

[8] Bianch FJ et al. Association between polymorphism in the promoter region (G/C-915) of PAX9 gene and third molar agenesis. J Appl Oral Sci 2007;15(5):382-6. doi: 10.1590/s1678-77572007000500002. PMID: 19089165; PMCID: PMC4327256. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4327256/pdf/1678-7757-jaos-15-05-0382.pdf

[9] Intarak N et al. Patterns of molar agenesis associated with p.P20L and p.R77Q variants in PAX9. Eur J Oral Sci 2022;130(2):e12855. doi: 10.1111/eos.12855. Epub 2022 Feb 19. PMID: 35182440. https://onlinelibrary.wiley.com/doi/10.1111/eos.12855

[10] Lee, WC et al. Association of common PAX9 variants with permanent tooth size variation in non-syndromic East Asian populations. J Hum Genet 2012;57:654–659. https://doi.org/10.1038/jhg.2012.90 https://www.nature.com/articles/jhg201290.pdf?pdf=button%20sticky

[11] Haga, S et al. A genome-wide association study of third molar agenesis in Japanese and Korean populations. J Hum Genet 2013;58:799–803. https://doi.org/10.1038/jhg.2013.106 https://www.nature.com/articles/jhg2013106.pdf

[12] Scheiwiller M et al. Third molar agenesis in modern humans with and without agenesis of other teeth. PeerJ 2020;8:e10367 https://doi.org/10.7717/peerj.10367

[13] Trakinienė G et al. Genetic and environmental influences on third molar root mineralization. Arch Oral Biol 2019;98:220-225. doi.org/10.1016/j.archoralbio.2018.11.026. https://www.sciencedirect.com/science/article/pii/S000399691830832X

[14] Weiss J. 3 April 2013. Missing Wisdom Teeth in Children: Are Anesthesia Injections to Blame? Medical Daily Retrieved 8 February 2023 from https://www.medicaldaily.com/missing-wisdom-teeth-children-are-anesthesia-injections-blame-244886

[15] Mann A. February 2013 Conference Paper: American Association for the Advancement of Science 2013 Annual Meeting. Wisdom Can Be Painful: The Evolutionary Origins of Third Molar Impaction in Humans. https://aaas.confex.com/aaas/2013/webprogram/Paper8686.html