I'm a bruxer and I recently had a crown that had fallen off replaced.
Prior to replacing the crown, the dentist had to file down the tooth
as he determined that the tooth had someone 'grown' since the last
crown was fitted. (Hard to believe as the original crown as only off
for a couple of weeks but that was his assessment.)
The nerve was precariously close to the top of the tooth and he did
advise me that there was a good chance that it would be damaged while
grinding down the tooth and I would need root canal.

A temporary crown was placed over the tooth and for the 2 week period
it was on, I did not suffer the symptoms detailedl below. When the
temporary was removed, and the 'regular' crown was being fitted,
repeatedly inserted and removed, I felt no pain at all. Moreover, when
the temp was removed and I flushed with water, I was surprised that
there was absolutely NO sensitivity--either with lukewarm water or
colder water. When the permanent cement was applied and the crown was
fitted, I was in EXCRUCIATING pain. This slowly subsided during the
period I was biting on an object so that the crown would set. I was in
some pain that evening. Since then, the tooth is very sensitive to
cold or hot fluids. In fact, the tooth is even mildly sensitive to
room temperature fluid initially. Moreover, there appears to be some
gum inflammation as well (indicated by flossing). The crown has been
on for a week, and while the pain generally has subsided, the tooth is
extremely sensitive to cold and hot fluids or food and the gum remains
a bit inflammed. Now, the bite inself is fine. I can chew basically
anything with minimal problems (other than those detailed above).

Here are my questions:

1) why did I not experience this extreme temperature sensitivity when
the temporary crown was on or when it was removed and the tooth was
exposed or when the crown was being repeatedly fitted without
adhesive? My dentist would have me believe that it is because the
nerve has been 'damaged' and I need a root canal. However, why weren't
these symptoms present prior to the permanent placement of the crown.

It seems to me that there is an exposed area in the tooth and the
permanent cement is pushing up against it and  needlessly aggravating
it.

2) why is the gum area between this crown and the crown directly in
front of it (that was inserted at the same time and shows none of
these symptoms) inflammed?

While I expect the gum area to get better, I can't really see the
extreme sensitivity improving (assuming that I'm correct in thinking
the permanent cement is aggravating the tooth).

Would removing the crown and  'covering' the exposed area be a
solution? Would temporary adhesive serve this purpose?