I feel your pain on this one. I have a very similar problem.
My parents enforced our dental care and we went to the dentist regularly when I was young. Always once a year checkup and twice a year cleaning and still I had regular dental issues.
In the second grade I can recall being brought out of class to a tooth-care specialist the school brings in to teach kids who seem uncared-for to brush their teeth. I brushed twice a day.
When I was fifteen I remember being yelled at by my dentist about how I don't look after my teeth because I had "16" cavities (the dentist, mind you, in my later years I realized was actually a bit of a hack -- all of his work fell out of my mouth and left me in terrible pain).
Around this time the dentist put me on regular fluoride mouth washes -- I went home with a bottle of some god-awful "cherry" flavoured stuff. I _still_ had repeated problems.
Fast forward to the present -- I've had one infected wisdom tooth, one infected molar -- both had to be removed. I have one half-decayed wisdom tooth that will be extracted soon. This fall I've had to have 4 fillings (some of them were put off for a while mind you).
The next year I am pending a root canal and a crown, and my dentist also has informed me that (at age 30) I require jaw surgery or I face the possibility of regular migraines due to molar wear.
I floss, brush, and use mouth wash daily. I don't eat much sugar. My parents actually raised us on a lot of raw vegetables (my mother grew, and I was raised in rural southern Ontario in Canada -- something of a agriculture belt).
The only neglect would be that my parents could not afford braces when I was young.
There has got to be some genetic aspect. Or does Hacker News as a consensus believe in shit luck?