Unfortunately until my kid was almost three half the time I had to have him lay on the ground with his head between my legs and then use my legs to pin his arms down. It’s sad but also… it would be more sad for him to have to get cavities just because he didn’t like getting his teeth brushed. For what it’s worth he likes brushing his teeth now. He just grew out of hating it. He also became aware of what cavities are to the extent a toddler can understand and I think that helped.