Well, I'm reeled in on this one even without Brian's asking, "I hope that one of the real doctors here from dental will post his observations."
My opinion Barb,
I believe from what you describe in your post that seeking the opinion from an ENT may be unnecessary. After reading and posting on this site for almost a year and with my training and experience as an expanded practice general dentist what you are describing is most likely a dental abcess.
Teeth sometimes become necrotic (die) for no apparent reason even in the absence of dental work, grinding and trauma. There is not always pain associated with a dead tooth and there is not always x-ray changes that show a change in the bone around the affected tooth. When a mobile fluctuant fluid filled mass appears on the gum by a tooth that is mobile or between teeth there are usually no radiographic changes associated with the tooth roots. ( ..this is where dentists have to earn their money, pun intended, because they have to climb the ladder of differential diagnosis.)
By your own admission you have undergone extensive dental work, grind your teeth and have had a recent extraction of an adjacent tooth. All of these could be potential contributors to the death of the tooth nearest the swelling.
I would suggest that your next step should be seeing the endodontist. It is obvious that you are not a fan of dentists and that is of no issue. It is obvious that you are in tune with your oral health from your descriptions in your post and I feel you know what you should do but, it is really not appealing to you. I strongly urge you to listen to your dentist, visit the endodontist and take the advice that Brian has already given to you..
There are three ways to determine whether or not you have an abcessed molar; 1, with local anaesthetic open access into the pulp chamber and see if there is pus, brown smelly goo, or blood in the tooth. 2, with local anaesthetic puncture the soft mobile lump and see if pus comes out of it. 3, Get a prescription for an antibiotic, (Amoxil 500mg 3 times a day for 7-10 days or comparable drug) and see if the swelling goes down or disappears completely. After all, an endodontic procedure (root canal) or draining of an abcess should be painless and is far easier on you than the rigors of cancer screening and diagnosis not to mention the increased time and emotional stress of waiting to find out what is going on.
I always remember my oral pathology professor's quote about this type of situation, "When you look in a horse barn look for horses they are obvious, the zebras are easy to spot."

Brian,
In my humble opinion, you provided up to date accurate information. Not your usual use of words but, certainly not flippant or condescending in my read. I have benefitted from your vast knowledge and have learned from you and your posts. You have been of personal and professional benefit to me, my family and my practice. I am a much richer person to be acquainted with you. (Praise deserved and Intended)
I have also benefitted from my local psychiatrists, psychologists and there wonderful chemicals. Many of you who have read a few of my posts know that I am not completely stable.

I hope the above was useful.
Contact me if you have questions.
Cheers,
Mike