My 17 mo will not let me near her mouth with a toothbrush. She used to be fine with it until her back teeth cut now she pushes it out with her tounge , shuts her mouth, smacks the brush out my hand etc. I don't want to make it worse or an ordeal by basically holding her down to do it. But I can't let this one slide. She will take the toothbrush herself but only seems to suck the toothpaste off and chew the brush... Any tips or advice?