Can the orthidontist tell

Question

when i patient has been smoking

Answer 1

they would know it, by smell & staining, but he won't be able to discuss this with your parents cuz of his privacy issues.  

Answer 2

Mine never brings it up and I'm 16.  On Final Destination 2 the dentists asks that kid if his parents knows he smokes while looking at his teeth.  If they can, it's unlikely they'd say anything about it.  Staining is caused by other things other than cigarettes, like coffee!