Can you sue an orthodontist if on the initial visit did not tell you how bad your previous orthodontist's work was and then later used the previous orthodontist as an excuse for lowering expectations?

it seems that you're trying to use negligence to sue your orthodontist. I'm no expert in law but based on the business law course that I've taken, i'd say you'd have to prove that your new orthodontist did not warn you of all risks/performed worse than average/deliberately w/held information to mislead you, etc.

how poor a job your former orthodontist did has no bearing here.