Researchers from the University of Arizona in the US think they may have solved the mystery of wisdom teeth, which may play a crucial role in tracking shifts in our evolution.
“One of the mysteries of human biological evolution is how the exact synchronization between the emergence of molars (or molars) and the history of life and how they were organized,” says lead author and anthropologist Halska Glowaka.
With the help of Gary Schwartz, a paleoanthropologist at the University of Arizona’s Institute of Human Origins, Gluaka collected examples of different skulls to compare their evolution.
By converting the bones and teeth of 21 species of primates into 3D models, the researchers were able to learn that the timing of our adult molars has a lot to do with the delicate balance of biomechanics in our growing skulls.
The adult tooth forms that we use to grind our food into paste, usually emerge from our gums in three stages – at around 6, 12 and 18 years old.
Other primates get their adult molars early. Despite all our similarities in developmental stages, chimpanzees (Pan troglodytes) get their molars at 3, 6 and 12 years. Yellow baboons (Papio cynocephalus) erupt their last adult molars by age seven, and macaques (Macaca mulatta) at age six.
An important factor limiting the timing of tooth eruption is the space. If the jaw is not big enough for an adult denture, there is no point in applying pressure on it.
And humans don’t exactly have as much mouth space as they do, with impacted wisdom teeth being a huge problem for our species. But that doesn’t explain why it appears so late in our lives.
However, having an empty space for a growing tooth does not make one appearing there as a good idea. And there’s plenty of muscle and bone supporting the teeth, ensuring that enough pressure can safely tear and grind our food. And it seems that “safety” is behind the development of our late teeth.
“It turns out that our jaws grow very slowly, likely due to our generally slow life history and, in combination with our short faces, delayed when there is a mechanically safe space, which leads to a delayed eruption of molars,” Schwartz says.
In primates, the posterior molars are located in front of the temporomandibular joints, which together form the joint between the jaw and the skull. And unlike other joints in our body, the two axes must work in perfect synchrony with each other. You also need to transfer a reasonable degree of force to one or more points to make you bite and chew.
In biomechanics, this three-point process is governed by principles within the so-called constrained plane model. Put the tooth in the wrong place, and the forces generated under this model may be bad for a jaw that is not large enough to handle.
For species with longer jaws, the time it takes for the skull to develop a proper structure for the teeth closest to the muscles near the joint is relatively short.
Humans, with our significantly flat faces, have no such luck, and need to wait for our skulls to develop to the point that the forces you place on each set of adult molars won’t harm our growing jaw.
Not only does this give us a new way to assess dental conditions, such as impacted molars, but it may help paleontologists better understand the evolution of our unique jaws among our ancestors.
“This study provides a powerful new lens through which to view the known links between tooth development, skull growth and maturation profiles,” said Gluwaka.