X-Rays

You may be concerned when your dentist tells you that an X-ray exam is needed. You may wonder whether it is really necessary, how you can benefit from it and whether or not there will be any risk to your health. This page provides brief, direct answers to these and other questions frequently asked about dental X-rays exams.

What are X-rays?

X-rays are a form of radiation that can penetrate many materials, including human bone and soft tissue. Since X-rays can also expose photographic films, they have become very important in both dentistry and medicine. People often use the word "X-ray" to mean the pictures made with X-rays. The proper term for an X-ray film, or "picture," is a radiograph.

How do X-rays work?

When X-rays pass through your mouth during a dental X-ray exam, more X-rays are absorbed by the more dense body parts (such as teeth and bone) than by the soft tissues (such as the cheeks and gums) before striking the film. This creates the image on the radiograph. Structures such as teeth appear lighter because fewer X-rays penetrate to reach the film. Other areas, including cavities and periodontal (gum) disease, appear darker because* more X-rays penetrate to reach the film. There is a whole range of shades of gray depending on the structures between the X-ray machine and the film. The interpretation of these X-ray pictures allows the dentist to detect hidden abnormalities.

What is the benefit of an X-ray examination?

Many diseases of the teeth and surrounding tissues cannot be seen when your dentist examines your mouth clinically. An X-ray exam may reveal the presence of small cavities between the teeth, infections in the bone, abscesses, cysts, developmental abnormalities and some types of tumors. A failure to diagnose and treat these conditions before obvious signs and symptoms have developed can threaten your oral and general health. Finding and treating dental problems at an early stage can save time, money and unnecessary discomfort. If you have a hidden tumor, early diagnostic X-rays may even help save your life.

What is a bitewing radiograph?

A bitewing radiograph shows the crowns of several upper and lower teeth on one small film. Films of this type are especially useful for showing cavities between the teeth and changes in bone caused by gum disease.

What is a periapical radiograph?

A periapical radiograph shows several entire teeth, including the crowns and all of the roots and some of the surrounding tissues on one small film. A periapical film can show many types of disorders, including teeth that are blocked from erupting (impacted teeth) fractures, abscesses, cysts, tumors and the characteristic bone patterns of some systemic diseases (diseases of the whole body).

What is a full mouth series of bitewing and periapical radiographs?

This is a series of bitewing and periapical films that show all of the teeth, roots and related areas of the jaws. The number of films needed depends on many factors, including the size and shape of the mouth and the technique used. Generally, at least 18 films are needed, but a full-mouth series may consist of as few as 14 or as many as 21 films.

The schedule for needing radiographs at recall visits varies according to your age, risk for disease and signs and symptoms. New 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-ray exams 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 dental caries (tooth decay) than those of adults.

What is a panoramic radiograph?

A panoramic radiograph shows all the upper and lower teeth, large portions of the jaws and other structures on one relatively large film. It is often used to find unerupted or impacted teeth, cysts, retained root fragments, fractures and other conditions of the jaws.

How often should I have dental X-ray examinations?

This 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 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.

How is X-radiation measured?

When human tissue or other materials are exposed to X-rays, some of the energy is absorbed and some passes through without effect. The amount of energy absorbed by the tissue is the dose. The dose is often measured in rads. Another unit of measurement, the rem, is used to compare the biological effects of different kinds of radiation. In modern diagnostic dental X-ray procedures, the exposure and dose are usually so small that they are expressed in "milli" units — that is, units that are equal to one-thousandth of a rad, or rem.

Should I have my previous X-ray films sent to my new dentist?

Yes, if possible. These radiographs can reveal your previous disease activity, the progression of disease, and the results of prior treatments, and they may assist in determining the need for a new X-ray exam. Although the dentist who treated you in the past is generally considered the owner of your records, including your X-rays, arrangements can usually be made to have X-rays duplicated and sent to your new dentist. You should contact your former dentist and request that this be done.

What scientific and government agencies advise dentists concerning the use of X-radiation?

The Center for Devices and Radiological Health of the Food and Drug Administration, the American Dental Association, the American Academy of Oral and Maxillofacial Radiology, the National Council on Radiation Protection and Measurements and many other organizations have developed recommendations on the proper, safe and effective use of X-rays in dentistry.

Individual state governments also have regulations regarding the use of X-radiation and X-ray equipment. By following these recommendations and regulations, dentists can obtain the diagnostic information that they need to effectively treat patients (maximum benefit) with the least possible exposure (minimum risk).

Prepared with the cooperation of the American Academy of Oral and Maxillofacial Radiology
© 1993 American Dental Association

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