Mouth sores can occur for a variety of reasons.
You may have a gum infection, tooth infection or you may have simply traumatized the tissue. If the sore has been there longer than 2 weeks and is not healing on its own, you should have it looked at by a dentist. The dentist may order an x-ray to help with the diagnosis. Healthy gums are not swollen and do not cause the surrounding teeth to be numb.