When brushing HB's teeth, we would have her open up and say "Aaah". That worked great for the back teeth, but we were still having a hard time getting her front teeth. Then, the idea hit me! I asked her to say "Eeeee". Eureka! Easy to reach front teeth.
She would also get bored of saying "Aaah" well before I was finished brushing her teeth. So, we play a game where I say it with different pitches. First a normal pitch, then a low pitch, then a high pitch. I mix it up and she has fun copying my pitch long enough to finish brushing.