Teeth Brushing

Evan is usually really good about brushing his teeth. He does a really great job but we like to make sure the back ones get done so we always finish up for him. He is usually pretty co operative about this but lately he's been more challenging. We have been doing the sticker chart. Every time he brushes he gets a sticker, and he is super excited to get a sticker. However, on the days he doesn't do a good job, or wont let us help him, he doesn't get a sticker. The problem is, he doesn't care if we don't give him a sticker. I don't get it. . . he's excited when he does a good job and gets a sticker but when we tell him he wont get one it doesn't seem to faze him. This morning I had to fight with him to let me brush and it resulted in tears. . . for both of us :( I have heard other moms say that their rule is "We do it the easy way or the hard way" The hard way meaning they usually have to hold their child down to brush. I did that this morning and I felt TERRIBLE!!!    I don't want teeth brushing to be a negative experience but how do we make him understand that it's non-negotiable? I read this article and we do most of these suggestions but it's like he has to be in the mood for it and when he's not in the mood he is super stubborn about it. Are our expectations too high? A part of me feels like he's still so young and to be more easy going but on the other hand I feel like since he's almost 3 that we should be more firm. What do you think?