Gap in gums after extraction and graft. Is this normal?

From what you describe it sounds like you had an extraction with a bridge temporary. As  you heal your gum will shrink as the swelling from surgery subsides. Sometimes they shirk more than expected. The space will continue to grow until you're completely healed, and then the space will remain the same. The space isn't anything to worry about, but you will want to get a proper fitting crown. You might need a new temporary made.  I would consult with your dentist and ask him about the space and the idea of another temporary. Also, make sure you have what you need to keep the area clean such as bridge threaders, and a water pic. 
Good luck!

Without seeing what you are referring to it is hard to determine if this is normal. If you have seen your dentist then you might to recheck with him. I would assume you are getting a small gap under the provisional tooth that is temporarily placed until you heal. Please note that gums do shrink as they heal even with a bone graft and as your swollen gums shring a small gap can develop. Usually this is normal and will be corrected in your final bridge. You should wait at least 8 weeks for the gums to heal before placing the final bridge. Good luck and heal well.

Yes, this is normal as the gums are healing after the surgery.  Over time, the gap size may increase as further healing progresses.