I Have Problems with Front 2 Veneers Coming off or Loose. Can I Replace Them with Crowns for a Stronger Bite and Stronger Teeth?

When I hear about problems with veneers coming off or getting loose I wonder what might be causing that to happen.  It is not the way it should be.  Since your other veneers are staying in place, I don't believe the problem is in the way they are bonded to your teeth.  The most common cause of this happening is related to the amount of stress or destructive force being put on those teeth.  This is caused either by the way you chew or bite, or by some habit such as clenching or grinding your teeth.  You say that you grind your teeth at night.  Grinding can damage porcelain crowns as well as veneers. 

You have 2 main choices.  1)  Repair the veneers and wear a protective night guard at night. or 2)  Have your "bite" evaluated by a dentist who practices with a neuromuscular approach and have this reconstructed to change the stress and alleviate the damaging forces that are being placed on your front teeth. 

I can feel the frustration in your question, and want you to know that you are not alone. Not only are you frustrated with loose veneers, but so is your dentist.  As you have experienced, veneers require proper equilibration of your occlusion ( balanced bite) and adequate tooth structure to retain them. In your case, it may be a question of one or the other, or both. My suggestion would be 1) to have your occlusion looked at and adjusted if necessary to avoid hitting those veneers harder than the others,  2) have a nightguard made to prevent you from clenching and or grinding at night, then have the loose veneers rebonded. If all else fails, perhaps there was inadequate tooth structure to retain them and then, crowns for those 2 teeth would be indicated. But again, the bite would definitely require adjustments so as not to chip and wear the opposing teeth. 

As most of the other doctors have indicated,  Your problems are either fully or partially related to your bite and in some movement your teeth are hitting to hard and popping off the veneers.  You are lucky none have broken which is common with a heavy bite on porcelain.  You should have the bite checked.  It is possible that they made your veneers longer for cosmetic reasons and they may be hitting now due to that reason.  Crowns are stronger, but if it is the bite, it will still cause problems.  Go in and get an opinion from a dentist or two and see if they agree on the problem and the solution.  Good luck!