Q: What do dentists call their X-rays?
A: Tooth-pics!

Explanation: I have never enjoyed going to the dentist, but it is necessary.  Every few years my dentist takes an X-ray of my teeth using those cardboard bitewings to get a good image of my teeth, and make sure there are no hidden cavities. X-rays use a small amount of radiation to see inside our bodies, and are really good for seeing teeth and bones.

A toothpick is a small piece of wood or plastic that is used to remove small pieces of food from between your teeth.

This joke is funny because it plays with the words tooth-pic (a picture of your teeth, pic is a shortened version of picture) and toothpick.

Take a look here to see how toothpicks are made-