Hello,
I was lucky my son took right to brushing his teeth. I would sit him on the counter beside me and give him his toothbrush so he could try and I would keep one for me. It usually worked that I would brush his teeth and he would play with his toothbrush in a little bit a water that I would leave in the sink. We made a game in pronounsing the AAAaa sounds and such to get him to open his mouth. Now that he is 2 we have gone down to one toothbrush. Sometimes we have some troubles with him not wanting to keep him mouth open for me but for the most part he lissens well because he gets his turn after I am done.