A. There is a huge misconception about grinding. Actually very few people grind thier teeth at night. If you do do then you have something called para function which meand the condition is habitual or you have a neurological disorder.
 In both cases if this was the reason then your teeth probably would have exhibited signs of wear before the veneers were placed and you should have been advised of fracture of veneers before hand.
 Also you would definately see some signs of wear on your back teeth. You may have muscle or joint problems. If you had none of these signs or symptoms then you are not a grinder. Without seeing you it is difficult to tell the cause of the wear but usually the reason for vertical fractures of anterior veneers is increased pressure on the teeth. Studies have shown that this is happens during chewing. The constant knocking of the lower teeth against the top teeth causes the bond to fail and this in turn causes the veneer to fracture because without the bond the veneer is extremely weak. This is all backed up by resaerch and studies. If your dentist places the new veneers in the same position as the old ones then the same thing will happen. It won’t make any difference if you wear a mouth guard or not.
Either your veneers were too long or they were locking your lower jaw back, or the palatal incline on them on them is too steep.
I hope this helps
Kind regards