My former employer/dentist gave out my private information to several people. Can/Should I sue him?

Ok, here's the story short: I am 22. I was a patient at a certain small dental office and later was hired by the same dentist while still working there. On several occasions I came to the workplace stoned (not OK, I know, but never once due while I worked there, he confronted me with it; in fact, he brought up several of the classic "stoner" movies as his favorites, and told a couple of half-hinted stories which made me believe he was/is a stoner himself). Anyways, I guess I was not doing my job properly (mostly, because there was nothing to do all day except to wait for someone call, and I would literally read books and play on my phone all the time, and he was OK with it. But I am digressing. A couple times while being his employer, I was also seen by him as a patient, and he filled a couple cavities and fixed a loose crown. He never mentioned anything to me about my "caries problem". Then, yesterday, my mother, who is also a patient of his, came for a regular check-up and asked him why I was fired. He named several reasons, among which mentioned his speculations about my weed use (and that once he found a bud at the workplace, but again, I was never confronted about that); but then also that I had a "root caries problem typical in people with a long-term history of drug abuse). Now, first of all, I do not use any prescription or street drugs except marijuana, and I certainly was not abusing anything of what he suspected me. That, however, made my mom freak out and begin thinking that I'm a heroin-shooting junkie or what-not. But what perplexed me the most is that he used my personal PATIENT information (not employee information!) to spread rumors about me and to speculate something that is not true. That should be illegal! I am over 18, so he cannot disclose such information to anyone, including my parents, without my consent! MOREOVER, apparently (according to what my mother said), he also disclosed the same or similar information with some other patients who happened to know me (at least they had a discussion of my drug use, which stemmed from "them seeing me at some party being stoned"). (I never figured out who it was, as I do not go to any parties. Ever.) Now, that is gossiping and spreading rumors behind my back by my dentist/employer. What I am afraid of is that now I will have trouble finding a new job because of the previous employer badmouthing me, and I am sure that he will use his "extensive dental knowledge" of my "Root caries" to justify his fears/speculations of my "methamphetamine/whetevercausestoothdeca… use and try to warn other potential employers. In addition to what is described above, he also did a lot of illegal stuff like not entering some patients' names into the computer database in order to charge them whatever special price he wanted while avoiding reporting that income and, therefore, taxes; or putting me, without any license or previous experience, to assist with the patient (i.e. to hold the suction tip in the patient mouth, etc). So, law-knowing people, what can I do to get him back (or at least to stop him from spreading nasty rumors to everyone who's willing to listen)? Please reply ASAP! Many thanks for SERIOUS answers!