Whether taking x-rays of your teeth or another area of your body, the denser an area is, the more it is absorbed and hence the less there is passing through to the sensor or film. Metal in general will block the x-ray from passing through and will appear white. Soft tissue such as skin and gums allow most of the energy to pass through, creating dark areas. Teeth and bone fall somewhere in between, enamel absorbing more, the pulp, or nerve, of the tooth less and shows darker. Likewise a cavity, abscess or missing cusp on a tooth will make that area less dense and will also show darker. All of these variations then create the image we see. The interpretation of these X-rays allows the dentist to safely and accurately detect hidden abnormalities.
How often dental X-rays (radiographs) should be taken depends on the patient’s individual health needs. It is important to recognize that just as each patient is different from the next, so should the scheduling of X-ray exams be individualized for each patient. Your medical and dental history will be reviewed and your mouth examined before a decision is made as to what type, how many X-rays are needed. Orthopantograms (pano, or panoramic) are taken by a machine which rotates around your head and show the entire jaw area from joint to joint, all of the teeth including the roots, sinuses nasal cavity and orbits. They give a great overall view but are not useful or clear in looking for cavities in between teeth. Bitewing x-rays are taking intraorally and show part of both maxillary (upper) and mandibular (lower) teeth at the same time and are much better for diagnosing interproximal caries (cavities in between teeth).
The schedule for needing dental x-rays at recare visits varies according to your age, risk for disease and signs and symptoms. Recent films may be needed to detect new cavities, or to determine the status of gum disease or for evaluation of growth and development. Children may need X-rays more often than adults. This is because their teeth and jaws are still developing and because their teeth are more likely to be affected by tooth decay than those of adults.