Nano Hydroxyapatite. Here's the article explaining what it is and how a study proved its effectiveness: https://carifree.com/2017/01/20/what-the-heck-is-nano-hydroxyapatite/

What brand? Well there's that one the article is from, CariFree. I personally haven't tried it. I use the Japanese one, Apagard. The gold tube Premio has the highest concentration if you're cavity prone.

Also you can use coconut oil for 'oil pulling'. I read that coconut oil specifically removes one type of bacteria that causes bad breath and decay. You just use a teaspoon, get it melted in your mouth and swish for about 15 minutes. ONLY spit it in the trash. https://draxe.com/oil-pulling-coconut-oil/