My Alzheimer's mom bites on the toothbrush while I brush her teeth. I am afraid that she will crack teeth. What can I do?

You can try the following techniques. We had similar issues with my grandpa.

We use to play music for our grandpa or sing a song with him. If that didn't work, we would all brush our teeth at a set time and tell him that he's not allowed to brush his teeth. That worked really well. You may miss a night but it's better than struggling with her.