When you visit the dentist to have your teeth checked, the dentist will ask you to lie back in a big, comfortable chair with a strong light overhead. She'll ask you to open your mouth while she uses a small instrument that feels like a metal toothpick. The dentist will go from one tooth to another, making sure that your teeth and gums are healthy. This procedure doesn't hurt at all.
Sometimes, the dentist will tell you that he needs to take "X-rays" of your mouth. This involves putting little pieces of cardboard in your mouth, which you bite down on. The dentist's assistant usually does this while you're waiting for the dentist to come back. While you're biting down on the paper, the assistant goes to another room to push the button for the big camera next to your mouth. The camera takes a picture using very powerful light called "X-rays." This light allows the camera to see inside your mouth as if your cheek wasn't even there.
X-rays allow the dentist to see inside your teeth, where cavities or other problems may occur that you can't normally see.