My mother has been experincing gritty food particles in her mouth on her tongue especially in between her teeth.  It started about 2 years ago shortly after she had a partial made for a couple teeth.  Her dentist can't seem to diagnois the problem and they can't see any build up of food particles when examining her, even though she feels the food particles with her tongue.  It is constant, never goes away, even after brushing, flossing with oral pic, and using the many mouth washes prescribed by her dentist.

Does anyone have an idea what this is and how it can be treated?