I used to get a small cavity every 2 or 3 years. My dentist recommended I switch over to a stannous-fluoride base toothpaste about 10 years ago and not a cavity since and my cleanings got much easier for the dentist. There is definitely some genetics to it too. I had a gf who was religious about her teeth routine, still had a small cavity almost every time and eventually a couple of crowns. She wouldn't lay off the sweets though. Never saw anyone who liked sweets as much as her.