Ionizing radiation revolutionized medicine and dentistry in the past century. It has well-documented benefits in orthodontics, and these benefits outweigh the risks. Three-dimensional cone-beam computed tomography produces images that contain significantly more information than do traditional radiographs but generally exposes patients to more radiation. A group of pediatric radiologists initiated the Image Gently Campaign to raise awareness of the need to adjust the radiation dose when imaging children. The key principles of this campaign are justification, optimization, and dose limits. Orthodontists should adhere to the directive to keep radiation “as low as reasonably achievable.” Prescribing radiographic imaging is specific to each orthodontic patient and requires judicious clinical judgment to maximize the benefits and minimize the harm.
Ionizing radiation revolutionized orthodontic practice and research in the past century.
CBCT images have more information than conventional images but expose patients to more radiation.
Key principles for radiographic imaging are justification, optimization, and dose limits.
Discovered by Wilhelm Conrad Röntgen (1845-1923) in 1895, ionizing radiation carries sufficient energy to displace electrons from within atoms or molecules. This process of ionization produces electromagnetic waves, commonly called x-rays. X-rays in this context must be differentiated from radiographs, which are the images of the human body used in medical and dental practices for diagnosis and treatment.
Röntgen acquired the first radiograph, which was of his wife’s hand, including her wedding ring. Upon seeing the shadow of her bones in the radiograph, she remarked, “I have seen my death.” Röntgen did not understand that his discovery would revolutionize the practices of medicine and dentistry.
Since Röntgen’s discovery, the evolution of radiography has been marvelous, especially over the past several decades with the advent and rapid development of advanced radiographic imaging, including computed tomography, interventional radiography, and a variety of other radiographic techniques.
However, the first half of the 20th century witnessed a different pace of advancement in radiography, particularly with regard to dental applications. The discovery of ionizing radiation toward the end of the 19th century coincided in an extraordinary manner with the development of organized orthodontics by Edward Angle, the father of modern orthodontics.
Orthodontic practice and research have benefited from ionizing radiation in numerous ways. For example, the advent of cephalometric radiography in 1931 by Birdsall Holly Broadbent (1894-1977) allowed orthodontists to more effectively diagnose and plan treatment for their patients. Additional benefits of this imaging technique, such as the ability to monitor growth and conduct accurate treatment progress assessment, are widely acknowledged. From a historical perspective, cephalometric radiography has the additional value of allowing orthodontic researchers to better understand and document craniofacial growth and development. Without this technique, several clinical questions would have remained unanswered to this day.
Cephalometric and panoramic radiographic imaging is the standard of care in orthodontic practice. Additional selected intraoral radiographs or a full-mouth survey is occasionally required, especially for adult patients or those with periodontal disease. These 2-dimensional radiographs are usually sufficient, especially when dental or other objects in the jaws need to be visualized in 2 dimensions. If visualization in 3 dimensions is desired, the use of cone-beam computed tomography (CBCT) may be more beneficial.
CBCT has a cone-shaped x-ray beam rather than a fan-shaped beam and uses radiation that is less than that for medical computed tomography, but more than that for panoramic and cephalometric radiographs. Recent developments of new CBCT models can use low radiation doses that rival those of panoramic and cephalometric radiographs, particularly for small-volume or quick scans. However, small-volume scans may be insufficient for orthodontic records; more importantly, these scanners do not represent over 40 commercially available CBCT models. CBCT scanners have vastly different fields of view, spatial resolutions, and radiation dosage ranges.
The benefits of CBCT in orthodontic practice cannot be ignored, especially because it provides 3-dimensional (3D) imaging. Evaluation of impacted or ectopic teeth, supernumerary teeth, root resorption, the pharyngeal airway, the temporomandibular joints, and all dentofacial abnormalities is enhanced with 3D imaging. Additionally, CBCT has provided a remarkable opportunity for orthodontic researchers to either confirm or refute the findings of previous research conducted with other radiographic imaging techniques, such as cephalometric radiography. CBCT also has the potential to assist in resolving hitherto unresolved complex cases and questions in orthodontics.
However, because children, who comprise a large portion of orthodontic patients, are particularly sensitive to radiation, it is imperative to adhere strictly to the directive to keep radiation “as low as reasonably achievable.” Ionizing radiation is a known carcinogen. Cancer formation from ionizing radiation is a rare stochastic effect with a latent period of several years or decades after initial exposure. Children have many years yet to live, allowing these risks to have increased probability to manifest later in their lives. Additionally, children have unique physiologic factors that make them particularly vulnerable to the deleterious effects of ionizing radiation. Low-dose radiation exposure during childhood results in a small, yet significant, increase in the lifetime risk of fatal cancer.
To estimate the stochastic health risk of any radiographic technique with ionizing radiation, the effective dose is commonly used. The effective dose is the sum of the equivalent doses to the organs and tissues exposed, multiplied by the tissue-weighting factors. When applied to children exposed to CBCT, this concept becomes problematic for several reasons. The tissue-weighting factors used to calculate the effective doses are averaged across all ages, a practice that ultimately results in neglecting the radiosensitivity of children. Also, children are smaller; this places several radiosensitive organs at higher organ and effective doses. For example, a 10-year-old patient would have a fourfold higher thyroid dose and a 30% higher effective dose than an adolescent patient, even if the exposure factors and the imaging protocols are the same. It is therefore important to fully justify CBCT acquisition in young children and increase the efforts to limit their radiation exposure.
To promote radiation protection in the imaging of children, a group of pediatric radiologists initiated the Image Gently Campaign, a campaign of the Alliance for Radiation Safety in Pediatric Imaging. This alliance is a coalition of health care organizations dedicated to providing safe and high-quality pediatric imaging worldwide. Its primary objective is to raise awareness in the imaging community of the need to adjust radiation doses when imaging children. The Image Gently in Dentistry campaign recommends selecting radiographs for each patient’s needs and using CBCT only when lower-dose imaging techniques cannot answer the clinical question that prompts the imaging.
In addition, the American Academy of Oral and Maxillofacial Radiology has significant concerns regarding the overexposure of children to CBCT. It supports the safe use of CBCT in orthodontics but recommends that its use be justified on an individual basis, according to the clinical presentation. Several, albeit not all, dental organizations share these concerns and recommendations. Moreover, the Food and Drug Administration recommends on its Web page that parents, patients, and health care providers should reduce unnecessary radiation exposure from CBCT.
One way to reduce unnecessary ionizing radiation exposure from CBCT is to follow appropriate selection criteria. For example, if conventional 2-dimensional techniques (eg, panoramic or intraoral radiographs) provide sufficient information for diagnosis and treatment planning, CBCT might not be required. If CBCT is required to visualize an impacted tooth, using a small volume should suffice. Interestingly, when an orthodontist owns a CBCT scanner, 2 concerns arise: the tendency for self-referrals to increase profits, and the tendency to read these images without consulting a radiologist, perhaps eventually leading to misdiagnoses.
Another important and highly ethical way to reduce unnecessary radiation exposure from CBCT is to avoid prescribing CBCT solely for research purposes. It is unethical to routinely prescribe pretreatment and posttreatment CBCT for prospective research subjects to produce data for future research projects. This would increase the collective effective dose for orthodontic patients and might ultimately cause harm to some.
Furthermore, there is a tendency in both practice and academics to compare CBCT dosage to a few days of background radiation. Most CBCT dosages are equivalent in magnitude to a few days of background radiation; however, the effect of short-lived acute exposure to CBCT of only a few seconds is unlike the effect of low and continuous exposure to background radiation, which is a source that humans are adapted to and cannot be controlled or reduced. It is thus better to adhere to the “as low as reasonably achievable” principle in radiation protection, particularly when dealing with young orthodontic patients.
In brief, ionizing radiation has revolutionized medicine and dentistry in the past century. It has well-documented benefits in orthodontics, and these benefits outweigh the risks. Nevertheless, each patient benefits differently from techniques requiring ionizing radiation, just as each patient benefits differently from orthodontic treatment. CBCT is an expensive technology, and 3D imaging does not necessarily improve the outcome of orthodontic treatment. The debate on the use of CBCT imaging in orthodontics will most likely continue. Some believe that it results in better patient care. Others believe that the evidence for its efficacy is lacking. In this 3D era, it is difficult to resist the lure of 3D images.
Nevertheless, cephalometric and panoramic radiographs appear to be sufficient in most circumstances and should not be replaced with CBCT imaging. Also, CBCT should never replace impressions or be used merely to represent a high-tech orthodontic practice. The prescription for radiographic imaging is specific for each orthodontic patient and requires judicious clinical judgment to maximize the benefit and minimize the harm. The key principles of the Image Gently Campaign are justification, optimization, and dose limits. It is imperative always to ensure that any radiograph is justified for the patient. When faced with complex orthodontic cases, we frequently consider the question, “What would I do if it were my child?” This question has proven to be equally helpful at the time of prescription to determine the most appropriate radiographs for each patient.