If the patient is suffering from lock jaw, what kind of orthodontic appliance should be given?

searching for the cause,begin with muscle relaxants the adjustment the bite with the deprogrammer.

must follow any complication in the  TMJ.

splint therapy to be started and followed by muscle examination and exercises

Deprogramming splint followed by myofunctional exercise.

Having oral surgery performed is another leading cause of this disorder. It is more common in people who have their wisdom teeth removed, however over the tenure of 1-2 weeks the problem typically and progressively resolves itself. Treating this disorder first starts with identifying the cause of it. With infection, immediate medical attention is required and medication. For the more common and less severe causes, a warm wash cloth may help relax the muscles and allow the mouth to open more fully. 

Absolutely agree with my colleagues above. I would start off with a night guard and jaw physiotherapy. Sometimes anti-inflammatory medication (Nurofen or any NSAID preparation) in combination with above can give a pretty decent outcome.