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The University of Basel, Switzerland, has found a new muscle layer in the masseter and described it in detail. The masseter is an essential muscle in the jaw which scientists have described as having a deep and superficial component. However, the team has found a third deeper layer.

The researchers now want scientists to name this muscle layer Musculus masseter pars coronidea, which means the masseter’s coronoid section. This name comes from the muscle layer’s attachment to the coronoid process of the mandible.

How researchers concluded the study

The researchers used MRI information from living people, computer tomographic scans, and the analysis of jaw muscles fixed by formalin. They also used stain tissues from dead bodies.

According to the lead study author  Dr. Silvia Mezey, University of Basel’s Department of Bioscience, the third layer serves a different function and course than the others. Moreover, its muscle fibers are arranged to suggest it plays a role in jaw stability. This layer is also the only one that can move the jaw towards the ear.

Other studies have suggested a third layer

This is not the first time scientists have suggested a third layer of the masseter. A 1995 edition of Gray’s Anatomy stated that the masseter has three layers. However, the book cited contradictory studies, some of which had examined the jaws of other animals.

Additionally, other studies from the 2000s described the masseter as having three layers. However, these studies detail one deep layer and divide the superficial into two.

Professor Jens Christoph Türp from the University of Basel’s center of Dental Medicine, the team decided to carry out their research because of the contradictory information on the masseter. The finding is monumental as many scientists assume that antagonists from the last 100 years have made every discovery necessary.

While most studies focussed on the muscle structure from the anatomist’s point of view, this study also looked at the opinion of dentists that focus on orofacial pain. As a result, they discovered the third layer, which many researchers have overlooked. 

The team has deduced the layer’s function by its build. Fortunately, they will conduct more tests to confirm their theory.