Can a dentist withhold original images of x-rays and send photocopies instead?

I requested copies of original images of my x-rays from my dentist and he sent me photocopies. I wrote him a letter requesting original images and not photocopies and he sent me another photocopy and a letter saying that I don't need original images since I am not trained to interpret x-rays. What should I do? I need to know if that's legal.