Denture irritation can be caused by more than one reason. Typically, a new set of false teeth will cause pain in the gums and mouth as you adjust to wearing false teeth. This pain should subside over the course of a few days or weeks as your gums heal. Loose-fitting dentures can slip and slide in the mouth rubbing gums and creating sore spots. Also, changes over time in our bone structure can alter the gumline to where dentures will not fit correctly causing irritation. Warped or damaged false teeth can cause sores in the mouth as well.