Seeking advice on teeth brushing / oral hygiene—how to accomplish?

What do you do when your loved one will NOT brush their teeth? He has very few left, and the bottom ones are covered in tartar. Nothing I do can make him brush his teeth.

Our dentist suggest he could chew on carrots, celery, even cheddar cheese to keep the mouth bacteria under some control. I read that the cheddar cheese is great for your teeth. Not only does it have high levels of phosphate and calcium, which naturally strengthen teeth and bones, but it also helps balance the pH level in your mouth, which means less harmful acid, more cleansing saliva and fewer cavities

This is just a wild guess, but I wonder if your dentist could recommend mouthwashes that are safe to swallow.  Most I've seen have chemicals in them, but there may be some natural ones that don't.

Thanks very much.

There are sponges that have toothpaste in them. They look like lollipops.

https://www.amazon.com/Disposable-Unflavored-Sponge-Cleaning-Toothbrushes/dp/B072MCFTFG