Can a doctor smoke and thus prove it?

Hello,

I'm 15 and have a dentist appointment tomorrow because I'm getting braces soon. My problem is that I've smoked weed twice in the last two months, taken half a pack of snus, and a little less than a pack of cigarettes. I know it's unhealthy; no one needs to tell me otherwise. My question now is whether the doctors will see this, and whether they're allowed to tell my parents because of confidentiality and all that.