Chin behind upper lip is genetic. It isn't CFD necessarily. It is actually very common especially in Caucasians. If you move your maxilla forward the relationship between the mandible won't change much. 

What is more likely to change is how far your chin goes in front of your nasion in the Frankfurt plane. 

And maybe 2-4mm if the stars align is my guess. That doesn't mean other aesthetic changes won't happen. But palate widening precedes maxillary upswing. What is your current Mew indicator score and palate width?

My palate has widened like 6mm and moved forward 1mm maybe. My incisors are retroclined though so it will be harder for me. I know if that changes my chin could advance in front of my upper lip .

Are your incisors retroclined ?

I havn't measured my mew indicator score, my pallate is narrow as i mouthbreathed when i got braces at age 15, prior to that my chin was relatively inline with my lower lip. My goal out of mewing/chewing is forward facial growth as braces have given me a decent allignment of the teeth though have also given me the expected craniofacial dystrophy symptoms, I remember the first 2 weeks i had them i could barley eat anything so i would assume a mouth breathing posture overnight due to sheer pain of closing the bite is what done most of the damage. And all my family members have inline/prominent chins so I dont think its a genetic cause. 

So you're saying that even after 6mm of paletal expansion you have only gained an estimated 1mm of forward maxilla growth? how long did this take you to achieve? and were you just mewing/chewing during this time?

I think EddieMoney said 1 mm per month expansion in 6 months or so in another thread. That is great in barely half a year, especially 1 mm forward.

Others have experienced mandible upswing within a year or so, which improved and stabilized within the following years. This probably comes from teeth realignment through expansion plus the minor forward gains, which realign the jaws. Maxilla movement and other facial changes such as cheeks & other upper facial features seem to take longer tho. Think in terms of 5 years if you are an adult.

EDIT: almost forgot. Depending on your inter-canine distance now studies have shown ppl gain about 3.2 mm distance within 8 months and lip change of 5.2 mm... so your lips may look very different in a year as well.

Posted by: Mewer000

I havn't measured my mew indicator score, my pallate is narrow as i mouthbreathed when i got braces at age 15, prior to that my chin was relatively inline with my lower lip. My goal out of mewing/chewing is forward facial growth as braces have given me a decent allignment of the teeth though have also given me the expected craniofacial dystrophy symptoms, I remember the first 2 weeks i had them i could barley eat anything so i would assume a mouth breathing posture overnight due to sheer pain of closing the bite is what done most of the damage. And all my family members have inline/prominent chins so I dont think its a genetic cause. 

So you're saying that even after 6mm of paletal expansion you have only gained an estimated 1mm of forward maxilla growth? how long did this take you to achieve? and were you just mewing/chewing during this time?

Mewing and slight chewing was what I did as well as posterior chain training in the gym.

That 1 mm increase took like 6 months, yes. But again, ortho retroclined my incisors so it will be harder for me I imagine to move forward more than laterally.