When we started fostering Tibbles, his mouth looked disgusting. After a few solid months of brushing every two days, not only has his plaque been reduced (scrapped off after a bit broke), a nasty tooth fell out and his gums and breath are a million times better. Please enjoy the following slightly graphic but happy pictures!
Teeth brushing; sometimes, you gotta scruff em, tuck their back paws in your arm pit and just do it.

ps: The phase two is just after brushing, which used to be a bit bloody because his gums were so irritated. He now no longer bleeds at all on most brushings.