I'm with Snoops and Barb on the Klonopin.
Mine helps my burning mouth, but has some very other nice side effects - my sensory symptoms (buzzing, tingling etc) decreased immensely, I was able to quit smoking cold turkey on it (from a very unhealthy 2 pack a day habit), it lowered my anxiety levels tremendously, and ultimately my stress levels... I can't say enough good things about the drug for what it's done for me.
I only take .25 mg 3 times daily. Very low dose.
For spasms, I upped my bedtime dose to .5 mg instead of my regular .25mg during a leg spam incident lasting a few nights, and it helped tremendously then too.

Was able to get through that and back to my lower dose.
The problems with Klonopin are that it's very habit forming, and tough to taper off (I've never fully stopped since I started taking it, but I know from missing a dose, the body reminds me!).