Now for the first study: 
Relationship_between_masseter muscle size and maxillary morphology

From what I understood, the cross-sectional area of the masseter is positively correlated with a the height of the anterior maxilla and negatively correlated with the height of the posterior maxilla, which is confusing and counterintuitive because that would essentially mean a higher bite force correlates with a clockwise rotation. Unless, of course, I misunderstood the terminology. But thats what this thread is for.. to clarify. 

Does somebody have the link to the study where the masseter muscles of monkeys got severed, which resulted in a downward growth of the maxilla? 

Posted by: @fiver

Now for the first study: 
Relationship_between_masseter muscle size and maxillary morphology

From what I understood, the cross-sectional area of the masseter is positively correlated with a the height of the anterior maxilla and negatively correlated with the height of the posterior maxilla, which is confusing and counterintuitive because that would essentially mean a higher bite force correlates with a clockwise rotation. Unless, of course, I misunderstood the terminology. But thats what this thread is for.. to clarify. 

Does somebody have the link to the study where the masseter muscles of monkeys got severed, which resulted in a downward growth of the maxilla? 

Higher bite forces usually result in Class 2 Div 2 cases if I remember correctly. Yes, the maxilla is up and forward, and the face shortens. Usually it creates a vertically short and square face with a weak lower third. Usually accompanied by a strong chin and obtuse nasolabial angle. 

Just because a Class 2, Div 2 maxilla is not downward grown, doesn't mean that this is a favorable outcome. Besides, human skulls in adulthood DO have maxillae that grows downward AND forward.

Posted by: @eddiemoney

Higher bite forces usually result in Class 2 Div 2 cases if I remember correctly. Yes, the maxilla is up and forward, and the face shortens. Usually it creates a vertically short and square face with a weak lower third. Usually accompanied by a strong chin and obtuse nasolabial angle. 

This is what I was expecting as a result, therefore my confusion:

(Quote from the Study)

As the masseter became larger, the anterior maxillary
region tended to shift downwards relative to the cranial
base, whereas the posterior region tended to shift upwards

Which sounds like chewing / jaw exercise results in exactly the opposite, of what we want. 

Posted by: @fiver

Posted by: @eddiemoney

 

Higher bite forces usually result in Class 2 Div 2 cases if I remember correctly. Yes, the maxilla is up and forward, and the face shortens. Usually it creates a vertically short and square face with a weak lower third. Usually accompanied by a strong chin and obtuse nasolabial angle. 

This is what I was expecting as a result, therefore my confusion:

(Quote from the Study)

As the masseter became larger, the anterior maxillary
region tended to shift downwards relative to the cranial
base, whereas the posterior region tended to shift upwards

Which sounds like chewing / jaw exercise results in exactly the opposite, of what we want. 

I mean at the end of the day, it delivers what it promises. A maxilla that is forward relative to the mandible, and facial shortening. Advantages are the face is vertically shorter. The chin gets stronger.

Disadvantages are a mandibular retrognathic profile, possible pug/anvil face syndrome, and weak soft tissue support. Basically the traits of a bad overbite. This comes with a brachyfacial structure that keeps the Mew line short (teeth close to the nose), but the overly clockwise rotated maxilla can make for a gummy smile at times, but not guaranteed unless tooth wear is extended. 

I think the fact that the maxilla ends up forward and upward draws people in as a great benefit. But then the mandible is too far up and back as a result, weakening the front view of the skull even more. Retroclined incisors (maxillary clockwise motion) create 0 overjet and weaken the smile.

One of the bad parts of this effect is that it in no way affects the midface ratio. The philtrum in many cases stays long (due to the retroclined incisors), and the eyes are unaffected. So if someone has a long midface ratio, they can still have it even if their face gets vertically shorter, since the vertical height of the lower third decreases, and the midface is untouched. As a result, short faced people with long midface ratios still occur. 

On the subject of phenotype, this seems to be a common trait in British people, to the point pug faces/overbites became very stereotypical.