The masseter muscle, on the side of your cheek, is the most prominent of the jaw muscles. Anatomy textbooks traditionally describe the masseter as a muscle formed by two layers: one superficial and one deep.
But a group of researchers in Switzerland claim to have discovered a section of the jaw muscles that has so far gone unnoticed: they described an even deeper third layer of the masseter.
“Although it is generally assumed that the anatomy of the last hundred years has found everything that could be found in the human body, our finding is equivalent to the discovery of a new vertebrate species by zoologists,” said study co-author Jens Christoph Türp in a statement. , professor at the University Center for Dental Medicine in Basel, Switzerland.
The researchers studied the structure of jaw muscles, CT scans, tissue sections from dead people who donated their bodies to science, and MRI data from living people.
They identified this deep third layer, associated with processes (bulges on the surface of a bone) of the mandible.
This process is called “coronoid”, which is why the authors of the research propose that this new layer be called the Musculus masseter pars coronidea.
​Szilvia Mezey, co-author of the study, explains that although the three-layered masseter muscle has been described previously, the existing literature is unclear about it and is sometimes contradictory.
The masseter is sometimes described as a single layer, sometimes as two, and when described as three layers, it was seen as a particular variation of some individuals, says the expert, who works in the Department of Biomedicine at the University of Basel.
“We wanted the reason for this inconsistency,” Mezey tells BBC News Mundo. “With our research, we realized that it wasn’t just a variation, it was consistent, the muscle was constantly there.”
According to Mezey, this newly discovered layer has a clearly different function than the other two layers of the masseter.
The first layer is responsible for elevating the jaw, the second helps to prevent it from going backwards or forwards; and the third helps to retract the jaw, stabilize and close it.
For the specialist, this finding is important for dentists and surgeons, as it indicates that the masseter behaves differently than previously thought.
In addition, says the expert, their research shows that we do not have the human body fully mapped and that we still have a lot to discover.
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