What could a small pebble-like lump under the tongue be after a temporary crown?

Hello:Not to worry, in most cases the crown with the post can be recemented without any problem.Best,Dr. Maddahi

Hi:My suggestion is to go back to your dentist to recheck the bite and do a nerve test to make sure nerve is ok.  Sometimes X-ray does not show nerve damage right away.Best,Dr. Maddahi

It is unlikely that decay under the crown of a root canaled tooth would cause the symptom you described. You should have the root canal result evaluated by an Endodontist to determine if all is well with the root canal procedure. Crack tooth syndrome is also a possibility. 

Hi:Depending on the amount of gum recession you have two choices:1.  Crown2.  Soft tissue grafting to cover the root of the tooth again.Best,Dr. Maddahi

The crown will feel big to your tongue and cheek because you haven't had a tooth there for a while. It takes about 2 weeks for your muscles to get adjusted to having a tooth there. If it still bothers you then the dentist can reshape the crown with a bur to make it more...

Hi:This could be part of a normal healing, however, its best to go back to your dentist and have the extraction site reevaluated.Best,Dr. Maddahi