to answer your questions, no, and no.
there is no possible way that a dentist could know FOR SURE if your dental problems were a result of methamphetamine usage unless the dentist ran a drug test on you (which is extremely unlikely, not only that but dental procedures aren't usually covered as much as "regular" doctor visits/exams/procedures would be by insurance - they should be (pretty sure they have to) ask you before they preform any type of exam or procedure that you aren't already aware of, and especially those not covered by insurance. I don't know many dentists who would pay for a drug test out of their own pocket just because curiosity killed the cat. Even if somebody walked into the dentist looking like an etch-a-sketchy, three-toothed bum, the dentist still couldn't be for sure if they were a drug user, or more specifically a meth user, unless the patient him/herself confirmed it as so, or a drug test (which won't be ran) is preformed. There's no little signs in your mouth that say "meth was here" or little white crystals dancing around on your bicuspids...
Secondly, no - it would be a breach of patient/doctor trust to divulge your information to anyone else other than his nursing staff or the insurance company, unless you told the doctor you were involved in serious crimes or were endangering the welfare of somebody else.
calm down, man...no reason to be so damn nervous. Hell - if anything, just be proud you're keeping up on your oral hygiene.