Are my teeth moving, or are my veneers loose?

It is unlikely that food is wedging underneath your veneers, but it is likely that your grinding issue is affecting your teeth.  I would suggest being re-evaluated for grinding.  Your night guard should be re-examined to determine if you need a replacement.  In the last 10 years of being a cosmetic dentist, I have seen some patients start to wear through their night guards after a few years.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMD

Our teeth have
thousands of tiny ligaments that hold them into place. Sometimes these
ligaments can get bruised or strained, especially in people that grind their teeth.
Are you clenching in the daytime? Did you forget your guard one night? Try
wearing your guard during the day to see what happens, and if they tighten up
in a few days. If not, it may be time for some x-rays.

Teeth
are in continuous movement due to a ligament they have, that works like a
support or as if it was a cushion. That receives and distributes masticatory
forces, and due to habits, or changes on the mouth, the teeth will adjust and change
position; meanwhile the biting is in process, the ligament distends and this
will make your teeth feel like loose, but they should be tightened to your
prepared teeth.

So I think your teeth could be just loose due
to this, but worry not it’s should only be a bite adjustment changing your
night guard should solve this. In any case you should visit your dentist about
this since it's hard for us to know exactly why is this happening without X-Rays and photos of before and now.