dd, 19 mo, and I stuggled for a while with this too. All of a sudden it became a power issue, I believe. Well, I lose sleep if she doesn't brush so I sort of forced her to do it, all the while thinking how I was going to traumatize her for life. I didn't hit her or anything but I pretty much forced the brush in there, which was the hard part. Once in she would relax, but still cry. Well, one day she just started to open her mouth when I showed her the brush and allowed me to brush. It's been like that for a week now, and I hope it continues.