A dog mouth cyst is like a lump or a bump in the mouth. It can affect the gums, teeth, or lips of the dog. In fact, as dogs get older, they become prone to all sorts of dental issues, such as an oral cyst. Most vets avoid calling a lump in the mouth a tumor except if the mass has been determined to be a type of cancer. Keep reading to learn more about oral cysts in dogs, the symptoms and causes, as well as the possible treatment options.