My son-in-law has been on Methadone for over 4 years now. His teeth are beginning to break off. Could it be caused from Methadone use. Also can a person be on Methadone the rest of their life or is there a time limit to be on Methadone. It seems that he has traded one drug for another. Oxycontin was his drug of choice and now he insist that he can not survive without Methadone.