For a super-tiny toothbrush, buy one for a cat.
I second Missy's advice. I took about a month to build up to actual brushing. Every night I would just brush one tooth and stop the second he wanted to, etc.
Thor still doesn't love it. He tries to turn his head away, especially when I do the front. Overall, he's pretty relaxed, though. He stays in my lap and falls asleep after tooth brushing. Nail clipping, he's gone the second I finish.