I use the Petzlife gel a couple times a week, Xena loves it and gets all excited when I pull it out. Izzy on the other hand, runs and I have to catch her to put it in her mouth.
I have finger toothbrushes but they still seem too big for their mouths, it's really hard to get their back teeth, I think I might try the gauze idea. I also buy regular toothbrushes and play with them with it and let them chew on it, I figure it's something and that's better than nothing.