I used to be able to brush my cat Ollie’s (R.I.P.) teeth. He was a strange animal though, he behaved much more like a dog than a cat, and did stuff on command. He was hesitant of course to let me brush his teeth but it worked. I wrapped him in a towel so he didn’t flail and used a small, SOFT toothbrush and brushed each section gently, stopped and pet him telling him how he’s a good cat etc… then the next section. He didn’t howl or anything he was just uncomfortable. Most cats will scratch, bite and completely freak if you try doing this, and its pretty pointless to be honest. Feed the cat some hard kibble or dental treats for the abrasiveness and it should be good enough.
The obvious way is to catch or purchase a mouse.
Cover mouse with generous coating of toothpaste.
Let nature take its course.
My cats’ teeth are routinely brushed, but it is a two person operation. In a closed bathroom one person holds the cat (burrito-wrapped in a towel w/ only head exposed) over their shoulder so it’s in an upright position. Cats don’t like the water trickling down from their teeth being brushed and there’s no benefit to holding them belly up. W/ one hand above their nose, keep their cheeks lifted; w/ the other hand brush the teeth w/ a fingertip brush and warm water rather than toothpaste; if the cat tries to chew the brush, let them. Then start again. Be gentle, stay calm, talk quietly to the cat; after several of these sessions it won’t be nearly as stressful for anyone involved, I promise. You can do it, OP!
I paid for one cat’s dental cleaning and not only was it hundreds of dollars, it was VERY stressful for her and she wound up w/ a bladder infection shortly after.