I think you're right about genetics. I'm 55 now and I've only had two cavities in my life (both in my wisdom teeth because I am one of those unusual people who has all 32 teeth and didn't need braces which means, according to my kids, that I have a big mouth :)). Anyway, I get super frustrated because I do brush twice a day, don't drink sugary drinks, chew sugar free gum and floss every day and still, tartar and plaque. My dentist says it's just my chemistry (and apparently handed down to my kids too).