Well, it is not a personal experience, but I know of a glider that has lost all of its teeth except for 8 or so (gliders have 40 teeth, so that means he lost around 32 of his). And his tongue hangs out all of the time, much like yours in this picture.
This glider is in the care of my breeders (they run a rescue as well). He was still a joey when this happened. This glider came to my breeders with multiple health issues (abscesses, infections, parasites, giardia, anxiety problems, you name it, he probably has suffered from it at some point in his life). When they took him to the vet, even they didn't think the glider would make. He had been pulled from a very young age, had been given a really bad diet (cat food and what not, if memory serves well), had lived in more than deplorable conditions, besides having being mistreated.
The people that rescue him, is a family that as mentioned breed gliders but also rescue animals (not only gliders). The wife has told me how she practically didn't sleep at all the first 2 weeks they had him. She would have to be giving medications around the clock (because of all the types of medications, they could only give him some at some point, and others at a different time), had to hand feed him (he couldn't feed himself), clean him (he would just go on himself), and just constant monitoring.
Even though, they miraculously managed to save him at that time (the vets couldn't believe it), the glider still suffers from a lot of health problems. He is very prompt to develop abscesses, suffers from sever anxiety, can only eat puree things, and so on. It is because of this that he became a permanent resident at their house, since nobody could care (financially, mentally and physically) for him.
Sorry for the long story, just wanted to share, and your post reminded me of the story of this little critter.
I am glad your glider is doing better now, and that he doesn't seem to affected from the lost of his tooth