Can True Polymorph be used to recover from diseases or curses?

Question

Say a level 20 human wizard named Dumbledore is tired of his hand hurting. Said appendage was damaged magically and cannot be cured by any known means (short of deity magic or a Wish spell, which apparently Dumbledore cannot cast). Will a permanent transformation of True Polymorph rid Dumbledore of the problem? Specifically, can a permanent True Polymorph:

1. Cure injuries, including amputations (I'm guessing yes)
2. Cure poisons, regardless of source (mundane, magical, etc)
3. Cure disease, regardless of source (mundane, magical, etc)
4. End curses, hexes, and similar effects

Answer 1

In order:

1. Yes with a but. Polymorphing into a fixed version of yourself is an easy application of the spell. This could also be achieved by polymorphing into a different race version of yourself, and then polymorphing back if people are really being literal about the "different" creature portion. Technically, you are different than the you from a second ago, but that's really just splitting hairs. The but to this comes with the persistence of the magical effect. If the injury was caused by magical means that are no longer present, but the wound lingers with magical damage preventing it from healing, then it's up to your DM to rule whether or not they'll permit polymorph to fix the damage. I personally would retain that kind of persistent effect through a polymorph and impose the significant wound on whatever form they took. Example: A wizard with a crippled arm polymorphs into an adult red dragon to fix his crippled arm. Upon completing the spell and making it permanent, the new dragon discovers that one of his wings is crippled in a manner very similar to the wizard's arm. You can see where that is going.
2. Yes, but only if you change into something that's immune to the poison that's affecting you. So ensure the thing you change into gets to keep your caster levels otherwise you're stuck. Like if you polymorphed into a vampire version of yourself, you wouldn't be poisoned anymore due to your immunity to constitution based effects.
3. Same as 2.
4. I would rule this no. If what you're looking at is ending a magical effect or becoming spell proof, this becomes a paradox. If what you're trying to change into is effectively spell proof, how are you casting a spell to change into it? However this is entirely dependent on the hex/curse.