How do you get gum sores?

CANKER SORES: Canker sores are small shallow ulcers that appear in mouth and make eating and talking uncomfortable.The exact cause is not known.Stress or tissue injuryis thought to be cause of simple canker sore.Certain foods like citrus or acidic fruits, vegetables likelemons, tomatoes, orange, pineapple, apples, fig and strawberries can trigger a canker sore.Braces, ill fitting dentures can cause it too.