I looked this up on Google and found this dental site:

http://www.dentistry.com/conditions/...mouth-syndrome

I have seen many places on the net that low B12 levels can cause this too.

If you have not had B12 testing, I'd get that ASAP. Your level should be 400 or above. Many doctors call lower levels "normal" because the labs used haven't caught up with the new standards. This is terribly out of date... as the link in my thread below is for DOCTORS to learn new things and is dated 2003!

I have a B12 thread here:
http://neurotalk.psychcentral.com/thread85103.html

It is suggested today that people 50 and over take B12 supplements because of the common incidence in older patients. B12 can be lost from taking acid blocking drugs every day for a long time, or use of metformin for type II diabetes.
People with autoimmune disease or gluten intolerance/celiac may also be low in B12 due to poor absorption.

There are also some studies showing triclosan in some dental pastes or other products may irritate the mouth as well. So check your labels.