Does methadone rot your teeth?

No. There is no specific correlation between Methadone and mouth hygiene. The only cause that comes to mind is a substance abuse behaviors in which taking drugs is more important than tooth hygiene. That stated, there is a clear association between methamphetamine and tooth decay. This is due to direct drug effect (poor salivation, teeth grinding) as well as poor hygiene.
No. Just maintain good oral hygiene and go to a dental professional for periodic checkups and cleaning.
N0. All the other drugs you have put into your system may have rotten your teeth, and you may have been so stoned you forgot to brush them.