X-rays are divided into two main categories: intraoral, which means that the X-ray film is inside the mouth, and extraoral, which means that the film is outside the mouth.
The various types of intraoral X-rays show different aspects of the teeth:
Bite-wing X-rays highlight the crowns of the back teeth. Dentists take one bite-wing X-ray on each side of the mouth. Each X-ray shows the upper and lower molars (back teeth). These X-rays are called “bite-wings” because you bite down on a wing-shaped film holder to keep the film in place while the X-ray is taken. These X-rays help dentists find decay between back teeth.
Periapical X-rays highlight only one or two teeth at a time. A periapical X-ray looks similar to a bite-wing X-ray, but shows the entire length of each tooth, from crown to root.
Periodically, a dentist may recommend a full-mouth radiographic survey, or FMX. This means that every tooth, from crown to root to supporting structures, will be X-rayed using both bitewing and periapical radiographs.
Occlusal X-rays are larger and highlight tooth development and placement. On each radiograph, nearly the full arch of teeth in either the upper or lower jaw is shown.
Extraoral X-rays are made with the film outside the mouth. These can be considered the “big picture” X-rays. They show teeth, but their main focus is on the jaw or skull. Extraoral radiographs are used for monitoring growth and development, looking at the status of impacted teeth, examining the relationships between teeth and jaws, and examining the bones of the face. Extraoral X-rays are less detailed than intraoral X-rays, so they are not used for detecting caries or flaws in individual teeth.
Panoramic radiographs show the entire mouth — all teeth on both upper and lower jaws — on a single X-ray. This type of X-ray requires a special X-ray machine. The tube head that emits the X-rays circles behind your head while the film circles across the front. That way, the full, broad view of the jaws is captured on one film. Because the machine moves in a set path, you have to be positioned carefully, and your head and jaw is held in place using devices that are a part of the X-ray machine. All this may look and feel intimidating, but the process is very safe and often uses less radiation than intraoral radiographs.
Cephalometric projections are X-rays taken of the entire side of the head. They are used to look at the teeth in relation to the jaw and the person’s profile. Orthodontists use cephalometric projections to determine the best type of orthodontic treatment.
Digital radiographs are one of the newest X-ray techniques. Standard X-ray film is replaced with a flat electronic pad or sensor. The image is electronically sent to a computer, where it can be viewed on a screen, stored or printed out. With digital X-rays, images taken at different times can be compared using a process that highlights differences between the images. Tiny changes therefore can be caught earlier.