Thanks for using Health Care Magic. Read your query. The symptoms you have mentioned suggests the condition called Bald tongue which is caused by a many etiological causes including anemia ,vitamin deficiency,infections,poor hydration having low saliva and also allergic reactions to tooth paste ,retainers and many others. I would advice you consult your doctor and start with multivitamis .If you take alcohol ,spicy food avoid this . The doctor will prescribe you a topical gel containing prednisone which will help in the healing. Consult the dentist before reusing the retainer.Maintain a good oral hygiene with proper brushing and flossing .Keep your oral cavity hydrated with having lots of fluids. Hope this was useful. Thanks and regards.