How likely is it that my veneers will come off?

It is not that likely, and your dentist is giving you good advice.  You have to ask yourself some questions. 1. Was the shape and appearance of teeth 7 and 10 affecting your life in a negative way before you got the veneers? (If you had "peg lateral" incisors, this common,congenital,condition is made to look great by conservatively doing just 2 veneers)  2. If you invested in a new set of tires for your car, would you get your car aligned and avoid driving through potholes to protect your investment and prolong the life of them. Your dentist is simply advising you on how to make your investment in your new, improved smile last without any potential problems.  We dentists are obsessed with prevention.  You should be able to bite into most things such as sandwiches, hamburgers normally.  It would be best for you to cut up apples into slices instead biting into a whole one.  Corn on the cob should be cut off of the cob. Bar-b-que ribs may be eaten it they are juicy, but if they are St. Louis style "dry" then you should pull or cut the meat off of the bone first.In the tire analogy above the Nightguard would be equivalent to the alignment of the car and mindfully eating certain foods would be like avoiding the potholes.  I hope this eases your concerns. Enjoy your new smile and share it with others everyday!Douglas Jopling, DDSDallas TX area