Kenneth Cheng, D.D.S.
Dental x-rays use electromagnetic radiation to create detailed images of a patient’s teeth and jawbones. Dentists can examine the images generated by an x-ray to detect abnormalities in the teeth or mouth that require treatment.
There are two major types of x-rays:
- Intraoral x-rays. Performed with the x-ray film inside the mouth, they focus on a small area of the teeth and jaw. They are the more common type of x-ray. Examples include bite wing x-rays and periapical x-rays.
- Extraoral x-rays. Performed with the film outside the mouth, they provide an overview of the jaw and skull. Examples include panoramic radiographs, tomograms and cephalometric projections.
X-rays are often used to monitor tooth growth and development in children. X-rays can also be used to reveal dental problems in patients of all ages. X-rays can reveal tiny pits of decay in the teeth that may not be evident during a visual examination.
X-rays can also be used to detect decay under existing fillings or other dental restorations, or abnormalities such as cysts, impacted teeth, extra teeth and tumors. Infections, periodontal (gum) disease, and injuries to the teeth or jaw can also be diagnosed with x-rays.
No special preparation is required prior to a dental x-ray. Typically, the patient sits in a dental chair and is covered from the chest to the thighs with a leaded apron. Depending on the nature of the x-ray, a film holder with a small piece of film may be inserted into the patient’s mouth and the patient may be asked to bite down on it. The camera is moved into place, and the dental hygienist, certified dental assistant or dentist leaves the room to take the x-ray. The entire process takes just minutes.
Patients generally have their teeth x-rayed on a regular schedule as determined by their dentist. The patient’s age and history of dental visits and dental problems help dictate how often a person needs x-rays. In some cases, x-rays may not be advisable. For instance, dentists generally err on the side of caution and do not recommend dental x-rays for women who are pregnant.
X-rays use very low doses of radiation to produce images. In high doses, radiation can have devastating health consequences for people. However, experts contend that the radiation dose used in dental x-rays is so low that it does not pose a health risk. Dentists and other dental professionals also take certain precautions, such as having patients wear a lead apron, to increase the safety of the procedure.
Dental x-rays help dentists to diagnose problems at an early stage, when treatments are less expensive, less painful and less time-consuming. In some cases – such as detecting a hidden tumor – dental x-rays can save a person’s life.
About dental x-rays
Dental x-rays are used to create detailed images of a patient’s teeth and mouth. They are created by a form of electromagnetic radiation in which the energy is high enough to penetrate the body and to create an image on film. Dentists can examine the images generated by an x-ray to detect abnormalities in the teeth or mouth that require treatment.
Objects and tissues in the mouth appear differently on an x-ray image depending on how many of the x-rays are able to penetrate the structure. The more thoroughly rays penetrate a structure, the darker it appears. Teeth and bones are relatively difficult to penetrate and appear in shades of off-white or gray (radiopaque). Because fillings or other metal dental restorations are often denser than teeth or bones, they show up as very bright white areas. However, the type of material used in the restoration dictates how light the image appears.
Parts of the mouth that are less dense or that contain air or fluid (e.g., cysts, tumors, infections) are more easily penetrated and appear either dark gray or black (radiolucent). Cavities show up as dark spots against the lighter-colored tooth. Infections and signs of gum disease also tend to appear darker. X-rays can differentiate particular parts of a tooth like enamel and dentin due to the differences in mineral content, which determines density.
X-rays are often used to monitor tooth growth and development in children. X-rays can reveal whether there is enough room in the mouth for the child’s permanent teeth to emerge and can detect abnormalities such as cavities, extra teeth (supernumerary teeth) and impacted teeth. When detected early on an x-ray, these conditions are often much easier to treat.
X-rays can be used to reveal dental problems in patients of all ages. X-rays reveal tiny pits of decay in the teeth that may not be evident during a visual examination. X-rays can also be used to detect decay under existing fillings or other dental restorations, as well as damage to such restorations and the following:
- Abnormalities such as cysts, infections and both benign and malignant tumors
- Bone abnormalities associated with diseases
- Infection, death of the nerve or other problems associated with the teeth and bones
- Injuries to the teeth or jaw (e.g., fractures)
- Periodontal (gum) disease
- Impacted teeth
- Extra teeth
A dentist may use a dental x-ray to help prepare and place dental restorations such as crowns, fillings, dental implants, and dentures. They are also used to plan orthodontic cases and aid in the diagnosis of traumatic injuries to the teeth and supporting structures.
Patients generally have their teeth x-rayed on a regular schedule as determined by the dentist. The patient’s age and history of dental visits and dental problems help dictate how often a person needs x-rays and the type of x-rays required. Some patients may need to have their teeth x-rayed every six months, whereas others will only require x-rays every two years. People visiting a new dentist are encouraged to ensure that previous dental records are forwarded to the new dentist.
Certain conditions and situations make more frequent x-rays likely. For instance, children are at high risk of developing cavities and need to have their tooth development monitored. As a result, they often need x-rays every six months to one year.
People with a history of extensive dental restoration may also require more frequent x-rays. Patients who have fillings and other dental work will require x-rays to ensure that decay has not formed beneath the restorations or in new spots.
- Tendency to drink sugary sodas, chocolate milk, or coffee or tea with sugar. These beverages create a much higher risk for tooth decay, making more frequent x-rays prudent.
- History of gum disease. More frequent x-rays may be necessary for patients who have a history of periodontal disease that puts them at increased risk of bone loss.
- History of smoking. Smoking increases the risk of periodontal disease.
- Use of medications or history of diseases or treatments that promote dry mouth. Certain medications, diseases and treatments cause a condition in which saliva production is reduced (xerostomia). Saliva keeps pH levels in the mouth stable and helps to cleanse the mouth. When pH levels fall, minerals in the teeth can break down, leaving the teeth vulnerable to cavities. Medications that can cause this condition include antianxiety drugs, anticholinergics, anticonvulsants, antidepressants, antihistamines, antihypertensives, diuretics and narcotic pain relievers. Diseases include Sjögren’s syndrome, and treatments include radiation to the head or neck that damages the salivary glands.
- Other suspected dental diseases.
Dental x-rays help dentists to diagnose problems at an early stage, when treatments are less expensive, less painful and less time-consuming. In some cases – such as detecting a hidden tumor – dental x-rays can save a person’s life. Studies suggest that dental x-rays may have value outside of dentistry, such as by helping diagnose osteoporosis or risk factors for stroke.
Types and differences of dental x-rays
There are two major types of x-rays: intraoral and extraoral. Intraoral x-rays are performed with the x-ray film inside the mouth. These x-rays help reveal cavities, the state of a patient’s tooth roots, the health of the bony area that surrounds the teeth and the status of the patient’s tooth health. Types include:
- Bite wing x-rays. Highlight the crowns of the teeth and provide images from the crown to the level of the jawbone. Each x-ray shows the upper and lower jaw in the back portion of the mouth. Bite wing x-rays can also show areas between the teeth that cannot be seen directly. They can detect cavities on the surfaces of teeth that touch adjacent teeth. These x-rays may be taken from the time a child’s teeth in the back of the mouth begin to contact each other.
- Periapical x-rays. Highlight the entire tooth from the crown down past the end of the root to the portion of the jaw where the tooth is anchored. Each x-ray shows either the upper or lower jaw in one portion of the mouth and typically captures information for two to three adjacent teeth. Periapical x-rays can be used to detect infections and gum disease.
- Occlusal x-rays. Highlight tooth development and placement. Each x-ray shows the full arch of teeth in either the upper or lower jaw. The x-ray machine may be pointed down near the nose or straight up from the chin, depending on whether the upper or lower jaw is being radiographed. Occlusal x-rays of the lower jaw are useful in detecting salivary stones (calcium deposits that clog the ducts carrying saliva). Occlusal x-rays of the upper jaw may reveal impacted or extra teeth.
- Digital radiographs. A new technique in which an electronic pad or sensor is used to record the x-ray instead of film. The recorded image is sent to a computer and displayed on a monitor. The radiographs that are taken can be digitally compared to earlier radiographs (subtraction radiography), offering a precise comparison of any changes. The technique is expensive and is not available in many dental offices. However, it is likely to become the standard process for taking images of teeth in the future.
Extraoral x-rays are made with the film outside the mouth, and provide an overview of the jaw and skull. These images are less detailed than intraoral x-rays, so they are not used to detect abnormalities in individual teeth. Instead, they are used to examine the relationship between the teeth and the jaw and to look at areas of the face (e.g., temporomandibular joint) that may be the source of dental problems. Types include:
- Panoramic radiographs. Highlight the entire mouth, including all the teeth, the temporomandibular joints and the sinuses. A special machine with a tube head circles around the patient’s head to capture these images. The patient must remain very still during the process, and is aided in this task with chin and forehead rests, side head positioners and bite-blocks. It is useful in detecting impacted teeth, jaw cysts and jaw fractures.
- Tomograms. X-rays performed to highlight one layer of anatomy while blurring out other adjacent layers. Tomograms are used to produce images of structures that are difficult to detect through standard x-rays. They are useful in detecting fractures of the facial bones.
- Cephalometric projections. Taken of the entire side of the head, they highlight the teeth in relation to the jaw from a profile view. These x-rays are often used by orthodontists to determine the best way to align teeth.
- Sialography. Highlights the salivary glands, which are not dense enough to show up on most x-rays. During a sialography, a radiopaque contrast material is injected into the salivary glands and appears on film to reveal blockages (e.g., salivary stones) and other conditions such as Sjögren’s syndrome.
- Computed tomography. Highlights the bones of the face and reveals problems such as tumors or fractures. This type of x-ray is usually performed in a hospital but some dental offices are now performing them to analyze bone structure for dental implants. A dentist may refer a patient for such a test if necessary.
Before, during and after the dental x-ray
Generally, no special preparation is required prior to a dental x-ray. However, patients with oral piercings may need to remove them beforehand. Typically, the patient sits back in a dental chair and is covered from the chest to the thighs with a leaded apron. In some cases, a leaded thyroid collar is placed over the patient’s neck.
Depending on the nature of the x-ray, a film holder with a small piece of film may be inserted into the patient’s mouth and the patient may be asked to bite down on it. The camera is moved into place, and the dental hygienist or dentist leaves the room and pushes a button that takes a picture. The entire process takes just minutes.
X-rays generally cause little discomfort. Some patients may find that biting down on the piece of film may cause gagging. Slow, deep breaths through the nose can usually relieve this feeling.
Potential risks with dental x-rays
X-rays use very low doses of radiation to produce images. In high doses, radiation can have devastating health consequences for people. However, experts have determined that the radiation dose used in dental x-rays is so low that it does not pose a health risk. In fact, the radiation associated with a single dental x-ray is much lower than the cumulative radiation people are exposed to every year from sources such as the sun, airplane travel, minerals in the soil and certain home appliances (e.g., smoke detectors, televisions).
Experts generally agree that the risk of leaving a dental condition undiagnosed and untreated is far greater than the risk associated with exposure to radiation from dental x-rays.
However, patients should be aware that even tiny amounts of radiation can damage cells, and that this damage accumulates over time with each additional dose. For this reason, dentists are careful to use the x-ray process judiciously and employ special precautions to protect the patient.
For example, dentists limit the scope of the x-ray beam to the precise area to be photographed. This process, called collimation, limits the amount of radiation that scatters to other areas of the body. Improved technology has also reduced the risk associated with x-rays. The speed of film used in dental x-rays has increased, meaning that less exposure is needed to obtain a good x-ray. Patients may also wear lead shields or lead thyroid collars that block x-rays from penetrating between their chest and knees. However, the lack of radiation scatter associated with today’s x-ray machines makes these shields far less important than they were in the past.
Federal law requires all x-ray machines to be professionally inspected for accuracy and safety every two years, and some states require even more frequent checks.
Eventually, it is anticipated that most x-ray procedures will be performed using digital radiography. This process reduces radiation by as much as 80 percent. Dentists generally err on the side of caution and do not recommend dental x-rays for women who are pregnant. Some studies suggest that pregnant women who are exposed to dental x-rays may have an increased risk of giving birth to low-birth-weight infants. However, dental emergencies may require pregnant women to undergo x-rays, as an infection associated with a dental condition usually poses a greater risk to the fetus than the small amount of radiation used in dental x-rays. Leaded aprons and thyroid collars can significantly reduce the risk of radiation exposure to the fetus.
Questions for your doctor about dental x-rays
Preparing questions in advance can help patients to have more meaningful discussions regarding their conditions. Patients may wish to ask their doctor the following questions related to dental x-rays:
- How often should I have dental x-rays? Why?
- What type of x-rays will you perform? Why?
- I’m concerned about the potential risks of x-rays. Can I have them less frequently?
- When was your x-ray machine last inspected for accuracy and safety?
- Should I wear a leaded thyroid collar for extra protection?
- Is my child at greater risk from x-rays due to his/her age?
- I’m pregnant. Can I put off my x-rays until after my child is born?
- Do you offer digital radiography?
- Will it cost extra to have digital radiography performed?