Is not it true that evolution completely failed us when it came to our teeth? Not only do the little biters begin to rot out of our heads as soon as we stop adding specific minerals to our water, but we do not even receive a full set until we are nearly old. The last of our molars takes an entire 18 years to develop, and they’re often the worst of the bunch, forcing themselves into our mouths at such absurd angles that you’d be forgiven for believing the phrase “wisdom teeth” was merely humorous. Our molars come in late compared to other great apes; the only other primate that comes close is the chimpanzee, which grows its final pair of molars at the age of 12.
However, why humans have to put up with this situation is a question that scientists have been debating for a long time. Two researchers believe they may have figured it out, according to a paper published in the journal Science Advances.
The study concludes, “Our findings support the hypothesis that the biomechanical limitation on masticatory shape in adult monkeys operates throughout the period of craniofacial maturation.” “When seen within the mechanical framework of overall orofacial growth, this limitation restricts where molars can emerge safely into functional occlusion, modulating the timing of when molars emerge.”
In other words, we will not be able to grow wisdom teeth until our jaws are large enough to accommodate them comfortably. Not that correct. However, the problem is that humans are strange creatures. We have large brains and small, receding snouts; it takes decades for us to achieve full adulthood, yet we will procreate several times before our firstborn is mature enough consistently avoid predators. When you try to translate the normal primate molar emergence times onto a species like that, things are sure to get a little wonky.
In a statement, study co-author Gary Schwartz noted, “It turns out that human jaws grow relatively slowly, possibly due to our overall slow life histories.” “[This] delays when a mechanically safe space — or a sweet spot,’ if you will — becomes available, resulting in our very late ages at molar emergence,” says the author. The size of our jaws, as well as the mechanics of our chewing muscles, determines the “mechanically safe” sweet spot. Molars that erupt too early, the researchers discovered, wind up in space and masticatory system that is not ready for them, and attempting to employ them results in a broken jaw joint.
The researchers discovered this delicate balance in nearly two dozen species of primates, ranging from little lemurs to gorillas. The researchers developed 3D biomechanical models of each species’ skull and chewing muscle development, which they integrated with data on each animal’s jaw growth rates. Humans’ late-onset wisdom began to make a lot more sense in this setting.
“Our data show that in H. sapiens, delayed molar emergence is the result of significant facial retraction combined with a slowing in orofacial growth and an extended length of orofacial growth,” the study concludes. “A delayed development of alveolar space in which molars can safely emerge is caused by the combination of orthognathic [the moving jaw] faces with protracted jaw growth.”
The implications for clinical dentistry are the finest part of the study — at least for anyone who has experienced the anguish of impacted wisdom teeth. Lead author Halszka Glowacka indicated that delving into some of the model’s deeper elements could help explain the painful event. “How the precise synchronicity between molar emergence and life history came about and how it is regulated is one of the mysteries of human biological development,” Glowacka added. “The long-known links between dental development, skull growth, and maturational characteristics can now be examined through a strong new lens,” says the researcher.