Tooth with Veneer Has Hole at the Back of It After Piece Popped Off During Flossing. What's The Cause? I'm Worried. (photo)

The photo does not show the space you are feeling.  I would have the dentist who placed the veneers look to see if you chipped a piece away or if it was excess cement.  Cement is hard to see after the veneers are laced and it is not unusual to miss a small piece which we find at your cleaning appointment.  

I tried to enlarge the photo to see what you are referencing but could not see anything.  If the hole you mentioned is between the two teeth, then it could have been a piece of cement that was pushing the gums back in this area.  If this is the case, sometimes the gum will fill in.

Have your dentist look at your concerns and see whats going on, hopefully, it was residual cement and not broken. However,if it is broken or chipped veneer it can be fixed or replaced.

 

Porcelain veneers are bonded with cement that is clear or white. If a piece popped out a few days after the veneers were cemented, then it is probably just a piece of extra cement that was trapped under the gum or between the teeth.

If this piece popped off more than a month later, it's possible that it's a piece of the porcelain itself. As the veneer meets the tooth edge, the veneer ultimately becomes paper thin. in some circumstances the tooth can flex and actually pop a small piece of porcelain off.

Odds are whether it was cement or even a small bit of porcelain, that it is still a minor issue.

A good cosmetic dentist will want you to have great results, so if you are still concerned about it, call your office, make an appointment and let him take a look at it. Even if it was porcelain, sometimes it can just be smoothed, or if necessary, that small section can be bonded. 

It's too early to panic. Let your cosmetic dentist take a look and you should be fine!