DS used to fight it a bit too. We sing the play school 'you brush your teeth' song and sometimes have to brush 4 or 5 other toy's teeth before it's DS's turn!

We also used to let him play with a toothbrush in the bath and giving him his own time and space with it seemed to be desensitising.

I think our biggest facilitator is DD though. He'll do pretty much anything she does. Have you got a cousin, neighbour or older friend who can play the cool big kid who just happens to need to brush their teeth?!