This will numb inflamed nerve endings. Use a new pencil to avoid infecting the sore with bacteria. This is an old remedy, but it still works. Stress and allergies are probably the most common cause of open sores in the mouth. Learn to relax and minimize stress from your life.
Some doctors prescribe mouthwashes that contain tetracycline, an antibiotic, for canker sores.
Do not use the same toothbrush for longer than one month. When brushing, avoid the affected areas with your toothbrush. Otherwise, you might scrape off the protective membrane that forms over a canker sore during healing.