I agree with the mom that suggested that you need to figure out why this is happening. She gave a lot of good suggestions. My curiosity is how is his communication?
Kids need a way to communicate if words are not working for them they will find other ways. Biting was one of the big ways for my oldest son. It took us a while to get him off of the biting, but it was after he learned a new form of communication sign language and then English. Some will tell you that sign language will prevent verbal language, that is not true. It has been proven to support it and when a child is having difficulties with verbalization, having another form of communication is important.
Don't assume just bcse he can say words that he knows how to communicate. My oldest daughter had tons of words and I thought she was just being difficult, but in reality she did not know how to communicate but had tons of words (she has autism). So is he able to communicate verbally to get his needs met, or is it possible that he is telling people, "Leave me alone, or that is mine", via his teeth?
Good luck, I know it is difficult with a child that bites.
One other thought, I have always found better success with telling my kids what behavior they should have used. "We use teeth for eating" or "When you want my attention touch my leg with your hand".
KP