At the beginning, BB was ok with 手指套. But after several weeks, he refused to open his month at all.
My friend gave me an advice and I find it works very well:
Buy a 細牙刷仔 and brush together with him. I used to bring him to the toilet, wet his 牙刷仔 (with water, no toothpaste) and put it just on the basin in front of him. Then I start to brush my own teeth. He will look at me first, then pick up the 牙刷仔 by himself and put into his mouth. I will let him do it by himself for a while (in fact he just 咬吓咬吓!) then I will help him 再補刷一兩下.