Sorry. I'm having a hard time imagining the exact
spotBirthmarks - pigmented
Liver spots
Measles, koplik spots - close-up
Mongolian blue spots. How are you feeling this hardness? With your tongue or finger? If its hardness and its pretty sturdy, it may be just your jawbone although I don't want to imply you don't know your own jawbone from something else. If it feels loose or moveable, it may be a broken piece of your jaw or tooth remaining in the socket. The gums will normally push out small pieces over a period of time. If it doesn't hurt or your symptoms improve, I would leave it alone and bring it up to your dentist next time. If it worsens, go see your dentist immediately.