How do I heal a sore in the mouth?

I recently went to the dentist and now have a sore on my gums/cheek direcetly underneath the teeth that I had work done on. I'm not sure if this is just coincidence and has something to do with when they worked on me. It's quite painful but I'm not sure if it's a canker sore or like I said something they accidently did. I don't know if I should go back to the dentist's office and ask or go my my medical doctor. Or just leave it. I just want to heal it and be done with it. I've been told to put salt on mouth wounds so I have been and it obviously totally stings when I do. What should I do?