Too Much of a Good Thing
Is as we all know it, bad for your health, specially when you consider that thing to be radiation exposure from x-rays. Studies and statistics are showing that many dentists order a lot of unnecessary 3D x-rays without considering the use of traditional 2D x-rays that would have provided the necessary information they needed.
This is true mostly for younger people who tend to get the best of the best even when older technology would suffice. This exposes you to more than the necessary x-ray radiation thus may give rise to more life threatening diseases so do ask your dentist if that is really what you may need.