Use a saline rinse. Rinsing your mouth with a saltwater solution can help disinfect your mouth ulcer, keeping it clean from the bacteria that naturally occurs in your mouth and preventing aggravation.1  Mix a teaspoon or two of salt with a warm glass of water.se a saline rinse. Rinsing your mouth with a saltwater solution can help disinfect your mouth ulcer, keeping it clean from the bacteria that naturally occurs in your mouth and preventing aggravation.