>Memes are inherited. You brush your teeth because your parents do. Memes are subject to selection via biological fitness. The people who didn't brush their teeth died sooner of tooth disease, so those who brushed their teeth had more children. Memes mutate. You don't brush your teeth identically to your parents.

That's parenting and the passing of tradition. I wouldn't call it a meme. Also I can't tell if you're joking with people dying due to teeth disease.

You explained the idea perfectly, which is a great way to see how flawed it is. To say the least, the main driver behind toothpaste adoption was not mass fatalities!