It is also possible to use arnica as a mouthwash for sore gums, or infections inside the mouth or tongue. A few milliliters/teaspoon of arnica oil in a gallon of water can make a perfect mouth wash. Arnica is also prescribed in low doses to chemotherapy patients who develop mouth ulcers, since it is known to help heal the wounds that form along the roof of the mouth and farther in the throat. Research conducted on dental patients showed that Arnica helped control pain and bleeding after treatment.