Fillings are done to remove decay, and replace the affected tooth structure. It is called a filling because a new material fills the hole that decay left. Now days most teeth are treated with bonded tooth colored composite resin fillings. Caught early enough, cavities can be treated easily and painlessly. If not treated decay can lead to tooth pain and/or infection, and the tooth would need root canal treatment or extraction.
This is used to fill in narrow grooves in a tooth that cannot be adequately cleaned by brushing. In some cases, the tooth structure has fine grooves or pits which accumulate plaque, not because the person doesn't brush, but because they're too narrow to allow even one bristle into them. These will develop cavities over time, and you don't want that. So the dentist will brush on a coating that seals the grooves and pits, making it possible to brush off all the plaque and keep your teeth healthy.
This is a focused beam of X-Ray particles through bone which produces an image on special film, showing the structure through which it passed. This gives the familiar black and white images that doctors and dentists use to diagnose problems. X-rays are a necessary part of the diagnostic process, and not to use them could lead to undiagnosed disease. Without an X-ray of the whole tooth, and supporting bone and gum tissues, there is no real way to detect infection or pathology that requires attention.
In our office we use digital radiography which allows us to take X-rays using 50-70% less radiation versus conventional X-rays. Coupled with computer monitorying, digital x-ray technology allows us to enhance the images for better diagnosis of any dental concerns.