I think if someone's teeth are overbite he needs an open embouchure. Pls. give me more information on open embou. On how to use the lips on ascending and descending notes. Where to place the tounge and placement when tonguing more and same notes... and others.
If the lips opening is not big and the muscles tends to move to center a little but also feels to smile a little (to make the mouth corners firmer) does he needs to feel a little buzzing to make a sound??
It's a list of different embouchures you can try using. It's a great resource. Personally, you need your teeth apart but enough to get sound. For pedal notes you would open your teeth even more. For high register notes, you would close your teeth half of a millimeter but still their open. For pedal notes, a Maggio embouchure is ideal. For high register, use a Farkas or a Steven's embouchure. But with Farkas you would have to work harder for the high notes and the mouthpiece is the only resistance there is, which is not healty.