"The arrangement of the muscle fibers, she says, suggests that this layer is involved in the stabilization of the lower jaw. It also appears to be the only part of the masseter that can pull the lower jaw backwards – that is, toward the ear."
What is lost in translation or reinterpretation in the quote you've posted is that retracting the mandible is either the function of the deep layer of masseter or instead the function of this newly discovered third 'coronoid' layer (or quite possibly, both); it is not as though anatomists thought 'how the jaw retracts' to be unanswered before today, but rather it seems they have been using an incorrect or perhaps incomplete picture.
Interestingly I can see the stark difference in depiction between Netter's diagram illustrating deep masseter [1] and this other one.[2]
I also note the description from Netters, which states that part of Masseter inserts on "the lateral surface of the coronoid process", describes pretty well the muscle being announced in this paper, as per their photographs.
[1] https://ranzcrpart1.fandom.com/wiki/Temporal_fossa:Masseter_...
[2] https://www.medspine.es/wp-content/uploads/2017/02/Sin-t%C3%...
My dentist told me I was grinding my teeth and prescribed a bite guard and within two weeks the pain got better but became very definitely focalized in the jaw and I noticed ‘popping’ as a symptom.
It has been about 1.5 years since the diagnosis. last summer I went through a phase of throwing a lot of random food into a pot and hitting it with an immersion blender, getting shakes from Burger King whenever I felt like it, etc. I lost almost 20 kg.
I have been eating more normally since, it doesn’t bother me very often.
It covers all the teeth on the top, but not the bottom.
My dentist said he could make one if that didn’t work out, but it did.
I’ve seen sketchy looking web sites by dentists who claim they can make something uniquely effective but it doesn’t look any different from the one I use so I don’t believe it.
https://www.byrdie.com/botox-for-teeth-grinding
and scientific review paper:
For the record, I am also blown away by how incompetent the medical and dental professions are at treating this. Tap your teeth on a piece of paper? Puh-leeze, that does nothing when your joints or muscles shift at different times of the day, and maybe 1 in 5 dentists actually know how to properly account for that based on my experience dealing with them over the years. And swear to god, if I hear another licensed and credentialed dentist describe my joint hypermobility as "your jaw is weird", I'm going to shit a brick.
So I'm not sure which of those (or both?) were the cause, but since removing my wisdom teeth I have worn a teeth guard every night, and I don't have that pain anymore.