Can't you get a doctor, nurse or dentist to teach you how to unlock your jaw by manipulating it with your forefinger?
I know my father could do it, both on himself and on patients, but I do not know how, not being a doctor-
You should also be able to avoid the problem to a very great extent by doing excercises that singers and actors do daily to relax the jaw.
These consist of relaxing your facial muscles with you mouth closed and your lips only lightly touching each other.
Open your nostrils wide and raise your soft palate as if you were about to sneeze, or yawn.
Then you drop your jaw, and open your mouth, taking care to do so slowly and keeping you tongue touching the backs of your lower front teeth.
Then gently close your mouth again, by moving your jaw upwards, still with your tongue in place along your lower front teeth.
Repeat five times.
NEVER use force and keep all your facial muscles as relaxed as possible.
Stop immediately, if you jaw, or its hinges hurt.
Take care when you yawn or laugh not to open your mouth too wide! And never repress a sneeze or try to disguise a yawn by keeping your mouth shut.