I have painful canker sores from time to time. I switched toothpaste brands to one for sensitive teeth and changed my toothbrush to a soft one. This seems to have reduced the number of occurrences. The last canker sore I had was the result of biting my lip. I used Colgate's Peroxyl antiseptic oral cleanser and within two days my canker sore was healed. It's the best thing I've found for curing a canker sore!