Your dentist is correct. If you grind your teeth, you are wearing them down . This will happen to your expensive veneers as well! Until you solve your problem, which is grinding, and find the reason you are doing this, whether it be anxiety, stress, or your bite and you are trying to adjust it by grinding or it has become a habit.....you need to eliminate this problem. Most dentists can diagnosis if your bite is off and correct it with a bite guard, the best bite disculder or an NTI Bite Guard. Some dentists use botox injections to relax masseter muscles and often, with this treatment, it helps retrain the correct facial muscles and your grinding stops. But you MUST take care of your bite, and then have your dentist do the veneers so you will be happy with your smile! Good luck!~