My 89 Year-old Mother Wears Full Dentures. For Several Days,

My 89 year-old mother wears full dentures. For several days, she has burning sensation on her gums. I took her to a dentist yesterday; he examined both her dentures and her gums, and said both looked good. He did not know why her gums "burn". Today, she said she is really "suffering". I don't know how to help.
My internet search informed me about a condition called burning gum syndrome. What I read leaves me unclear still as not only how to help her with pain, but I don't even know what kind of doctor to take her to. She is 89, suffers a bit of dementia, and has a low tolerance for pain. Any suggestions?