How do dental X-rays work?
When X-rays pass through your mouth during a dental exam, more X-rays are absorbed by the denser parts (such as teeth and bone) than by soft tissues (such as cheeks and gums) before striking the film. This creates an image called a radiograph. Teeth appear lighter because fewer X-rays penetrate to reach the film. Tooth decay, infections and signs of gum disease, including changes in the bone and ligaments holding teeth in place, appear darker because of more X-ray penetration. Dental restorations (fillings, crowns) may appear lighter or darker, depending on the type of material used for the restoration. The interpretation of these radiographs allows the dentist to safely and accurately detect hidden abnormalities.
How often should radiographs be taken?
How often 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 form the next, so should the scheduling of X-ray exams be individualized for each patient. Your dentist will review your history, examine your mouth and then decide whether you need radiographs and what type. If you are a new patient , the dentist may recommend radiographs to determine the present status of the hidden areas of your mouth and to help analyze changes that may occur later. If you have had recent radiographs at your previous dentist, your new dentist may ask you to have the radiographs forwarded.
The schedule for needing radiographs at recall 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.
What are the benefits of a dental radiograph examination?
Many diseases of the teeth and surrounding tissues cannot be seen when your dentist examines your mouth. An X-ray examination may reveal:
- small areas of decay between the teeth or below existing restorations (fillings);
- infections in the bone;
- periodontal (gum) disease;
- abscesses or cysts;
- developmental abnormalities;
- some types of tumors.
Finding and treating dental problems at an early stage can save time, money and unnecessary discomfort. It can detect damage to oral structures not visible during a regular exam. If you have a hidden tumor, radiographs may even help save your life.
How do dental X-rays compare to other sources of radiation?
We are exposed to radiation every day from various sources, such as frequent airplane travel and high altitudes, minerals in the soil, and appliances in our homes (like smoke detectors and television screens).
| Source | Estimated Exposure (mSV*) |
| Dental radiographs Bitewings (4 films) Full-mouth series (about 19 films) | 0.038 0.150 |
| Medical radiographs Lower GI series Upper GI series Chest | 4.060 2.440 0.080 |
| Average radiation from outer space In Denver, CO (per year) | 0.510 |
| Average radiation in the U.S. from Natural sources (per year) | 3.000 |
Source: Adapted from Frederiksen NL. X-Rays: What is the Risk? Texas Dental Journal. 1995;112(2):68-72.*A millisievert (mSV) is a unit of measure that allows for some comparison between radiation sources that expose the entire body (such as natural background radiation) and those that only expose a portion of the body (such as radiographs).
What if I’m pregnant and need a dental radiograph examination?
A radiograph may be needed for dental treatment or a dental emergency that can’t wait until after the baby is born. Untreated dental infections can pose a risk to the fetus, and dental treatment may be necessary to maintain the health of the mother and child. Radiation from dental X-rays is extremely low. However, every precaution is taken to minimize radiation exposure. A leaded apron minimizes exposure to the abdomen and should be used when any dental radiograph is taken. A leaded thyroid collar can protect the thyroid from radiation, and should be used whenever possible. The use of a leaded thyroid collar is strongly recommended for women of childbearing age, pregnant women and children. Dental radiographs are not contraindicated if one is trying to become pregnant or is breast feeding.
Some people worry about their exposure to radiation during dental X -ray procedures. This is very understandable in light of the relatively high radiation of some medical X-rays. They may remember a doctor in the emergency room asking them or a female family member if they are pregnant because they need to take a chest X-ray or an upper gastrointestinal (GI) series. Patients who have had cancer may also have a heightened sense of awareness about the radiation that they are receiving at the dental office.
Dentists are very concerned about minimizing the amount of radiation a patient receives at the dental office. That’s why we use special high-speed film, and cover patients with a lead apron during X-ray procedures. You will be happy to know that 18 dental X-rays deliver 56,000 times less radiation to an unborn child than an upper GI series, 800 times less radiation than a chest X-ray, and 40 times less radiation than a typical day of background radiation. Dental X-rays are both safe and effective, and can be used during pregnancy.
One new dental technology involving dental X-rays is digital X-rays. They offer the advantage of an 80 percent reduction in radiation, no need for film or processing chemicals, production of a nearly instantaneously image, and the ability to use color contrast in the image.
With digital radiographs, film is replaced with a flat electronic pad or sensor. The X-rays hit the pad the same way they hit the film. But instead of developing the film in a dark room, the image is electronically sent directly to a com puter where the image appears on the screen. The image can then be stored on the computer or printed out. One of the great advantages of this process is that radiographs can be digitally compared to previous radiographs in a process called subtraction radiography. The computer can digitally compare the two images, subtract out everything that is the same and give a clear image of anything that is different. This means that tiny changes that may not be noticeable with the naked eye can be caught earlier and more clearly with digital-subtraction radiography.
Panoramic radiographsshow the entire mouth area – all teeth on both upper and lower jaws – on a single X-ray. This type of X-ray requires a special panoramic X-ray machine. The tube head that emits the X-rays circles behind the patient’s head, while the film simultaneously 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, the patient has to be positioned very carefully. And, because the beam and the film are both moving, any movement from the patient will blur the image on the screen. That’s why such care is taken to keep the patient’s head absolutely still in exactly the right position. The machines may have chin rests, forehead rests, and side head positioners, plus bite-blocks that patients will be asked to close their teeth around. All this may look and feel intimidating, but the process is very safe and often uses less radiation than intraoral rad iographs.