QUOTE(SueHM @ Mar 13 2009, 01:52 PM)
On the other hand, I was told by a brass teacher that the mouthpiece actually rests on the jaw/gums rather than the teeth and hence has no effect on tooth development.[...]
My front teeth take some of the load when I play the horn with a mouthpiece slightly larger than a cornet one. Was your informant specifically referring to trumpet, cornet or orchestral horn mouthpieces? I would expect trombone mouthpieces to rest on the gum of the upper jaw, but for the lower teeth to be somewhat involved, with a fairly light load.