About a month ago, my dentist put a temporary crown on one of my teeth
using temporary cement.  He told me it might come off, and to call him
if it did.  Three weeks later, it came off while I was eating ice
cream, so the next day I saw him to get the permanent crown put in.

He was going to use permanent cement to put in the permanent crown, but
I told him that I had felt some discomfort whenever I bit down hard on
the temporary crown.  So he said he would just use temporary cement
with the permanent crown, and that if it felt OK for a few weeks, then
he would use permanent cement on it.

One thing of concern is that after he used the temporary cement with
the permanent crown, he tried to floss between my teeth, and the crown
came off when he lifted the floss.  He was very surprised by that, and
didn't think it should happen.  He reapplied the cement, and told me
that I'd have to pull the floss out from the side instead of pulling it
up.  He also said that after I get the permanent cement put in, there's
no way that I could pull off the crown using floss.

That was one week ago.  Yesterday, while eating ice cream again, the
permanent crown came off!  I understand that it was only temporary
cement, but why does it seem so weak?  And why does it always come off
when I eat ice cream??

I called my dentist and will go in this afternoon, presumably to use
the permanent cement this time.  But I wonder if maybe the crown
doesn't fit right?  And could the permanent cement be weakened by ice
cream?  I'm afraid the crown will come off even after he uses permanent
cement.