I have a black spot about the size of a pin-head in my left inner cheek. It has been there for the past twenty years. I always have problem in my left side of the face such as inflammation in inner cheek, slight irritation in my outer cheek, ulcer in my inner cheeks, inflammation of gums. I was a heavy smoker once. Now I smoke two cigarettes daily. I consulted several doctors. They ruled out the possibility of cancer. How to cure this problem