I'm recently diagnosed with mild internal derangement of tmj. can anyone tell me if this condition is curable or not?

Yes!: It is curable, but many things need to be kept in mind: is it simple( like a night guard) or complex( like complete crown and bridgework). These two items can be addressed by you dentist. Remember, almost anything can be cured in the short term, but can it be maintained in the long term. Good luck

Depends: Depends on your symptoms. Mild "internal derangement" which is usually a displaced disc, requires no treatment if your symptoms do not trouble you. Once a disc is displaced, it is out of position period. If it bothers you, see a TMJ expert.