I recently got a cat/dog toothpaste from my vets called Pet Dent. Cost about £5, and you use it with either a pet toothbrush or a baby's tothbrush. It has a taste that my cat absolutely loves, and he'll even lick the tube to try to get some more, but unfortunately it's been quite difficult to actually brush his teeth! I do manage it a little, so I would say it's worth trying.