a story of hope
One of my chinchillas, Emma, came to me from the local shelter. She was in bad shape, and it turned out (after visiting several vets, the last one being the local university veterinary hospital and their exotics specialist, who took several x-rays) that she had overgrown teeth roots (and the topsides of her teeth were not good either). Her teeth were ground down, and I was told much of the information in this thread, including what to look for to signal that it was time to euthanize her. She was given pain meds for the duration, and wasn't expected to survive beyond a year. The exotics vet also, however, put her on a strict diet of nearly exclusively hay (NOT pellets) supplemented with greens like dandelion leaves and wild lettuce (and for a while, dried nettles - boy these were SUPER fun to try to collect, but they were appreciated by both of my chins) - no mention, specifically, of vitamin C or calcium supplementation. Actually, if I recall correctly (and I may not be, admittedly) he (or perhaps another of the vets) suggested that I LIMIT calcium intaKe (which, mostly took the form of alfalfa hay).
Well, I nursed her through this initial period, and the pain meds helped. Finally she was eating on her own and acting like a chinchilla, but I monitored her very closely for a long time (and kept her on the pain meds for a long time, too), and did have her teeth ground down a few times (obviously we couldn't do anything about her roots).
Well, as amazing as this might sound, it is over 6 years later (she is 9+ years old), and her teeth roots, in subsequent x-rays, actually appeared to RECEDE, and her overall dental health has improved - she has not needed her teeth ground down for a while now.
I can't explain this, nor can the vet, really (except to say that the almost exclusively all-fiber diet and lots and lots of chewing is healthy and sometimes has surprising effects), but everyone is thrilled.
I'm SO sorry to hear of the fate of so many other chinnies with this issue (I thought Emma's would be the same), and I'm not sure why or how I got so lucky (although I'll admit, her nickname became my "million dollar" chinchilla), but this story is true. There IS hope.