C.D.
My daughters were not happy about teeth brushing either, but are fine with it now. Here's what helped:
* They use their toothbrushes to do it themselves and when I brush I use a finger toothbrush.
* They choose the position to brush in - standing, on my lap etc.
* The toothbrush talks to them every night and asks them what is on their teeth and they say penguins, elephants etc. I ask how many and they tell me. Then as I brush I count the number of animals toothbrush has gotten and the animals make noises as they are running away and assorted silliness. I sometimes sing:
"I'm gonna brush those penguins off of your teeth
I'm gonna brush those penguins off of your teeth
I'm gonna brush those penguins off of your teeth
And send them off to play"
To the tune of "I'm gonna wash that man right out of my hair"
Totally silly but it works - and if they laugh their mouth is wide open, so all the better.