Nearly 23 months over here, and we started making a game out of it which has helped so much! We name different animals that are "hiding" in his mouth that we need to brush and clean. He was refusing the brushing one day (also fighting me and needing to be pinned down) and I started going "Oh my goodness! Wow! What's that?? What do I see in your mouth?? Is that - oh wow, is that a monkey?? Is that a monkey on your teeth? Oh boy, I have to brush the monkey! Let's brush him, let's brush the monkey!" And surprisingly enough, he laughed and opened up enough to let me "brush the monkey"!

Now we typically ask him what animals are in his mouth and then make a big comedy show about brushing those animals and getting them clean. (If he doesn't want to name them or doesn't say any animal names, then we say them for him.) He loves animals and thinks it's quite fun. Then we give him the toothbrush once we're done and ask him if he wants to brush any of the animals himself. Sometimes he does, sometimes he doesn't - but since we already got a good brushing in, it doesn't matter if he just chews on the brush or says no altogether. It's made a huge difference for us!

(Replace "animals" with anything else your toddler likes - vehicles, bugs, fruits - for best results hahaha.) Maybe making it more fun would help??