Burning Mouth & Loss of Taste

I have been wearing an "appliance" for nearly six months every night for my severe TMJ.  Was sent to a particular dentist who specializes in this treatment to re-seat the joint and ostensibly get rid of some of the migraines.  Was referred by the neurologist.  I might add I have had a nightguard for years but this is, of course, different.  It's taking quite a long time--longer than most people, I'm told--to see any positive effect with this.  All was going along until about six weeks ago when my mouth starting burning upon eating or drinking almost anything though there are no visible signs of this.  I thought it might be due to some highly spiced food I had had but that was months ago.  Now, I have lost my sense of taste also and have almost no saliva.  I asked the dentist if this could be an allergy to this appliance and he insists "no" --that it's made of some acrylic or something similar.  I might add I have a slight B12 deficiency and I understand burning and lack of taste might be symptoms of that but mine isn't that severe and I am taking supplements.  It's not getting any better.  Initially they tried to blame my toothpaste but I've tried several kinds and I doubt this is it. Any ideas?  Could it be the appliance?

[Regalhank]

Thank you.  Upon researching further on the net, many neuromuscular dentists advertise a neuromuscular "treatment" to relieve TMJ problems.  What might this "treatment" involve?  How would it be different than this appliance that I wear every night to re-seat the joint? How can I un-impinge the nerve?