As for the position Master Lin says to have the tongue touch the roof of the mouth. Is some material it is fine to have just the tip touching, but I recall (but not where) I heard that as you progress Master Lin would like you to have greater contact.
Now is it the position of the tongue or the contact that is important? For this one I consider the self-demonstration of using sword fingers to draw circles on our own hand. Then doing the same thing through the table. Then I think of how one can use qigong to do distance healing. Then finally that qi healing is energy - information - signal - prayer - love healing.
I would think that as a total novice you can direct qi through a table and across several inches of open air, then the denture will pose no great barrier to the movement of qi.
You are perfection.
Iam2 
