I try to brush Boop's teeth. I manage at least 5 days out of 7 using Petrodex brand toothpaste. I think that's the name or something much like it. She loves the flavor. At first I tried the small end of a two-ended doggie tooth brush, but it was really too large. Then I tried a soft plastic thimble with bristles molded in, but it was still too large. Now I'm using 4" - 5" lengths of a gauze roll, from the bandage section in the drug store, dampened and rolled around my finger tip with a dab of toothpaste. It's a bit of a nuisance and doesn't scrub all that well, so if anyone has a better idea I'd love to hear it.
I also give her chews that are ground-up rawhide compressed back into a strip and also made by Petrodex. They are supposed to have some of the same enzymes the toothpaste contains. I think. I tossed the packaging. She's so small she only gets a half, and she loves them.
I have high hopes for the toothpaste and the chews because she refuses kibble, cookies, any baked treats.