Would my dentist know i smoke and can he tell my parents?

Are you really 42 ?: That's what your profile says. If you are 42, your dentist cannot tell your parents without your permission. And yes, your dentist will be able to tell that you smoke.

Dentist can tell: Your dentist can tell that you are a smoker. There are many signs that are evident in you teeth and mouth. Your dentist will not disclose any information unless you give permission.