Hi.. Thanks for the query.. Soreness at the bottom of mouth can be secondary to infection while as your mother is wearing false teeth soreness can be due to any sharp edge over the denture plate causing injury to soft tissues under the tongue causing inflammation and pain.. You should consult an Oral Physician and evaluated and a thorough clinical evaluation can help in diagnosis.. In case if the inflammation is secondary to infection in sinuses then treatment of sinusitis will relieve the inflammation under tongue also.. While if t is due to sharp edges on denture it can be relieved by smoothening the sharpness over the denture.. As of now you can take symptomatic treatment like application of numbing gel containing Lignocaine or analgesic gel containing Choline Salicylate.. You can take Ibuprofen for pain and inflammation relief.. Take a soft diet and maintain a good oral hygiene.. You can also do cold compresses and rinse with cold water.. Till the healing occurs limit the wearing of the denture to prevent further irritation.. Hope this helps.. Regards. Dr. Honey Arora.