I went to the dentist yesterday for my biannual oral abuse and got an X-ray series as well. While I was being draped with the lead apron, a couple of questions came to mind.
Q1–What is the benefit of shielding my torso and nads? I did after all receive several high-energy bolts right through the head.
Q2–Why lead? What is it about lead that shields X-rays? Its mass? Is it unique among elements in its shielding properties or is it merely the cheapest solution?
Lead is used in medical areas for radiation shielding because it’s cheap and dense enough to be effective without needing a ton (literally) of it. You could get the same shielding for your X-ray with an apron of concrete a couple feet thick. That would probably not be as comfortable as a lead apron. There are some more exotic materials that will shield radiation as well as or better than lead at a fraction of the mass, but they would bankrupt a dentist’s office.
They shield the rest of your body for the reason that Slick said. Anything to minimize your exposure to excess radiation is good. There is also a bit of CYA on the dentist’s part. If you would get cancer some years down the line, you couldn’t come back at them in some way.