A Answers (3)
Dental x-rays take pictures of the mouth and teeth which show the densities of the different tissues. Dental cavities can show up in these pictures before the cavities are seen in a visual exam. Dentists take x-rays periodically to keep track of changes in the teeth, usually every one to three years.
American Dental Association answered
Dental X-rays are a useful diagnostic tool when helping your dentist detect damage and disease not visible during a regular dental exam. X-rays show the areas under the gum, such as roots of teeth that cannot be seen otherwise. It is in these areas where tooth root decay can form and lead to cavities.
Jerry Gordon, Dentistry, answeredA dental x-ray can show areas of potential tooth decay because those areas look darker (less opaque) on the x-ray than a healthy tooth. Training and experience allow the dentist to interpret the x-ray and determine the appropriate course of treatment.