How to brush a Great Danes teeth?

I have a Great Dane, She is about 9 months old and is starting to get plaque at the base of her teeth, she is very sweet and lets me mess with her mouth and lips, but I don't know how to expose her teeth with one hand and brush with the other, since she has large jowls. Any techniques anyone has mastered? I also give her chew toys, so it should be easy to prevent it from getting any worse by brushing right?