Why Are So Many Teeth Crooked? What Ancient Skulls Suggest
Crooked teeth are a modern phenomenon and a telltale sign of an underlying epidemic.
Crowded and crooked teeth are much more common in people today than in skulls from earlier centuries. The main explanation is that soft, processed modern food gives the jaws less chewing work while children are growing, so jaws end up slightly smaller than the teeth they need to hold. Genes still matter, and diet is not the whole story, but the evidence for a dietary influence is consistent.
What do old skulls show?
A study from the University of Oslo compared 146 skulls from abandoned medieval graveyards in Oslo, Norway, with a modern Norwegian sample assessed with the same orthodontic index.
About 36 percent of the medieval skulls showed an objective need for orthodontic treatment.
In the modern sample, the figure was 65 percent.
Severe cases were also more common today: 20 percent of the modern sample showed great need, compared with 7 percent of the medieval skulls.
The authors concluded that both how often malocclusion occurs and how severe it is have increased over the last several hundred years in that population.
Why would diet change jaw size?
Bone responds to the forces placed on it. Chewing tough, raw or lightly processed food puts more strain on the jaws and face than chewing soft, cooked food, and that strain helps drive growth.
In 1984, anthropologist Robert Corruccini reviewed populations around the world and described a rapid rise in crooked teeth and bite problems as groups moved to urban, industrialized diets. He argued the speed of the change pointed to environmental causes rather than genetic ones.
In 2004, a team led by Harvard's Daniel Lieberman raised rock hyraxes, small animals with a short face somewhat like ours, on either raw and dried food or cooked food. The animals fed cooked food had about 10 percent less growth in the lower and back parts of the face, where chewing strain was highest.
Lieberman later described this pattern for a general audience in his 2013 book The Story of the Human Body, as one example of a mismatch between modern life and the bodies we inherited.
What are the limits of this evidence?
Skull studies compare populations, not individual people. They cannot tell you why your own teeth are crowded.
Genes influence tooth size, jaw shape and bite. Habits such as thumb sucking and mouth breathing may also play a part.
The animal research shows a plausible way diet affects jaw growth. It does not show that a tougher diet today would straighten an adult's teeth.
What does this mean for you?
Crowding is common, and having it does not mean anyone did something wrong. Crooked teeth can be harder to clean, which raises the risk of decay and gum disease, and a poor bite can wear teeth unevenly. Whether treatment makes sense depends on your teeth, your bite and your goals.
If you are weighing options, you can read about clear aligners, how smile design compares with orthodontics, and why wisdom teeth sometimes have too little room. In Jacksonville, a dental examination is the place to start.
Sources
Evensen JP, Øgaard B. Are malocclusions more prevalent and severe now? A comparative study of medieval skulls from Norway. Am J Orthod Dentofacial Orthop. 2007;131(6):710-716. doi:10.1016/j.ajodo.2005.08.037. Retrieved via PubMed.
Corruccini RS. An epidemiologic transition in dental occlusion in world populations. Am J Orthod. 1984;86(5):419-426. doi:10.1016/s0002-9416(84)90035-6. Retrieved via PubMed.
Lieberman DE, Krovitz GE, Yates FW, Devlin M, St Claire M. Effects of food processing on masticatory strain and craniofacial growth in a retrognathic face. J Hum Evol. 2004;46(6):655-677. doi:10.1016/j.jhevol.2004.03.005. Retrieved via PubMed.
Lieberman DE. The Story of the Human Body: Evolution, Health, and Disease. New York: Pantheon; 2013.
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.
A Greenland Fossil Jaw and the Origin of Molars: Summary
Scientists have described the earliest known example of dentary bone with two rows of cusps on molars and double-rooted teeth. The new findings offer insight into mammal tooth evolution, particularly the development of double-rooted teeth.
In 2020, researchers described a fossil jaw from eastern Greenland, about 215 million years old, that has the oldest known molar-like teeth with two roots and two rows of cusps. It belonged to Kalaallitkigun jenkinsi, a mouse-sized close relative of the first mammals.
The study, published in the Proceedings of the National Academy of Sciences, also used engineering models to show that teeth with two roots withstand the forces of biting better than teeth with one root. That may help explain why broad chewing teeth and divided roots evolved together, a design human molars still carry.
For the full explanation, including what the researchers found, the study's limits and what it means for your own molars, read What a Tiny Jaw From Greenland Shows About the Origin of Molars.
Sources
Sulej T, Krzesiński G, Tałanda M, et al. The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals. Proc Natl Acad Sci U S A. 2020;117(43):26861-26867. doi:10.1073/pnas.2012437117. Retrieved via PubMed.
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.