Maybe I'm missing something ...but your profile indicates that your son has been diagnosed with multiple issues. You are also a board member for the Autism Society San Diego. Why does it surprise you that he has been having problems? Your expectation that he is just going to tow the line and follow direction seems unrealistic, given his diagnosis. As far as cavaties, there are multiple reasons; some kids have a genetic pre disposition to them, sometimes the water is not flourinated, and sometimes their diet increases the likely hood of dental problems etc. It's not always just poor brushing and flossing. It sounds like your frustration has increased to the point that you are personalizing everything he does as a direct attack on you. Maybe he is...but chances are, with his diagnosis, you are just seeing who your child is. My stepson has aspergers (and possibly ODD-though never concretely diagnosed) and we would (and still at 18) go round and round because he would not follow specific direction. From cleaning the bathroom to completing homework to washing his hands. I used to tell his therapist that I wasn't sure if he was aspergers or a**hole! I know it is a lesson in frustration and it feels like you're being disrespected. That is a hard thing to accept. I finally saw some improvement when I lowered my expectations, and stopped being so critical of everything he did, or did not do. That helped him relax a bit.
I think getting any teenager to correctly complete chores all the time is near impossible, unless you're living in a Brady Bunch sitcom...and even they had a full time maid! Obvioulsy, you've got lots of stuff happening, but maybe you need to start to change some of your reactions to his behavior, in an effort to get him to change . Just a thought. Good luck.