Since my last dental cleaning (they said I had no cavities), I started
feeling what seemed to be a cavity (dull ache after eating or drinking) in
one of my upper bicuspids, which has no filling and no visible problems.
About a month ago, it got worse and anytime food or drink touched it, it
hurt and I noticed it was really cold sensitive. To make things worse, my
two molars next to the bicuspid started feeling like they were cracked, and
whenever I chewed on something hard, it would hurt a bit on the molars.

Well I just went back to the dentist, and he did x-rays, spent a lot of time
looking them over closely, tapping my teeth, etc., and could find no signs
of cracks or cavities in any of the teeth. He did the tooth sleuth thing and
5 cusps hurt a bit when he did that, but because they are on the two
adjoining molars, he thought it would be highly unlikely that the two teeth,
right next to each other, would crack at the same time.

He also tested my bite several times and couldn't find anything that needed
to be "ground down" or anything. He said I was experiencing cold sensitivity
on the bicuspid, and that he ws absolutely sure that there was no crack or
cavity of any kind in this tooth, which he said was in great condition.
There was nothing wrong with my gums neither, he said. The only thing he
could come up with was that I was clenching a lot and I did not realize it,
but I've never had a clenching problem and there's no new or major stress in
my life that would cause this, so I doubt that is the case.

Since I've returned from the dentist, I've realized after testing with cold
and warm foods that it is cold sensitivity that's causing the pain in the
bicuspid, not a cavity like I originally thought. Now I'm trying to figure
out what has changed to cause this sensitivity over the last several months.

I'm thinking that, about the time of my last cleaning, when I started
feeling like I had a cavity,  I had switched to a new toothbrush that is
pretty firm. Plus, about a month ago, when the cold sensitivity got really
bad and when I started feeling like my molars next to the bicuspid were
cracked, I had a spot on my upper gums, next to the bicuspid and molars,
that felt like there was a popcorn kernal stuck under my gums. It was a
little sore and swollen in that spot, and I spent several days flossing that
area over and over and brushing that area of my gums harder than normal,
trying to get the trapped food out.

Eventually it must have came out, because the sore spot on my gums went
away.

Now I've switched my toothbrush to a softer one and I make sure I don't
brush hard like I used to. But can a hard brushing of the gums cause major
cold sensitivity, even though when I touch the gums there's no pain on the
gums, and the dentist couldn't find anything wrong with my gums? Likewise,
since all these 3 teeth are next to each other, could a hard brushing of the
gums cause a feeling in the nerves, when I chew on something hard, like they
are cracked?

And most importantly, now that I've switched to a softer brush and am more
gentle in my brushing, will the nerves/gums heal and the cold sensitivity
likely go away?

Thanks in advance for your help!