General guidelines for radiographic acquisition

From a purely risk management perspective, not taking a clinically necessary radiograph is worse than taking an unnecessary one. Beyond risk management, it is widely considered beneath the standard of care to initiate orthodontic care without first acquiring proper diagnostic information. A clinician who begins orthodontic treatment without appropriate radiographs necessary for creating an adequate and appropriate diagnosis and treatment plan may be breaching the standard of care.

Radiographic imaging is justified if there is an expected benefit to the patient. No dental organization or any authority can make clear rules on when and which radiographs to take, because each clinical encounter and each patient are different. A minor finding during a clinical examination could make or break the decision on which radiographs to take, if any.

The American Dental Association and the Food and Drug Administration provide general and broad guidelines for dental radiographic examinations and recommendations for patient selection. For new adolescent and adult patients with permanent dentition, they advise an “individualized radiographic examination consisting of posterior bitewings with panoramic examination or posterior bitewings and selected periapical images; a full-mouth intraoral radiographic examination is preferred when the patient has clinical evidence of generalized dental disease or a history of extensive dental treatment.” These recommendations were made for dentistry overall but not specifically for orthodontics.

The process of prescribing radiographs in orthodontics is based on the practitioner’s clinical judgment for a particular patient’s presentation, and the ALARA directive—keeping radiation as low as reasonably achievable—should be adhered to. Because most orthodontic patients are children, the ALARA directive is heightened in orthodontics.

In general, the justification for taking radiographs is based on each patient’s presentation including considerations of the chief complaint, the medical and dental history, and the requirement to diagnose, monitor, or examine the need, status, or outcome of a procedure or treatment. Radiographs should always be prescribed after (not before) a clinical examination has been performed.

Initial radiographic acquisition in orthodontics

After reviewing the patient’s health history and completing a clinical examination, radiographs should be considered if they are likely to provide confirming or clarifying information that can affect the diagnosis and treatment. Because each patient is different, there is no indication for taking a standard or the same series of radiographs for all orthodontic patients.

To establish a comprehensive diagnosis for most orthodontic patients, case-specific radiographs are necessary for the patient’s benefit. With the ever-increasing quality of radiographic machines and images, the combination of pretreatment panoramic and cephalometric radiographs appears to be appropriate and sufficient in most cases.

For initiating orthodontic therapy, a panoramic radiograph has many advantages and provides much information, including the status of dental development. This single image provides an excellent and broad view of a variety of structures, including maxillary and mandibular dentitions, adjacent structures, and temporomandibular joints, and is quite helpful for patients with asymmetry. The panoramic radiograph is simple to obtain and easy to interpret and explain to patients.

Whereas a panoramic radiograph of good quality can show a significant amount of information, it comes with 3 main limitations. First, it lacks the fine detail required to diagnose and monitor carious lesions and periodontal status, and the objects outside the focal trough will not be shown in detail. Second, the panoramic radiograph is not dimensionally accurate and may include geometric distortion and unequal magnification throughout the image. Third, panoramic radiography requires the patient to be positioned accurately in the focal trough. To do so, it is valuable to follow the manufacturer’s recommendations for patient positioning, including the appropriate use of light beam markers. Staff members should be able to identify patient positioning errors and optimize the quality of patient positioning during panoramic radiography.

The value of the initial cephalometric radiograph, when appropriately acquired, should not be ignored. It can be useful for assessing growth and dental and skeletal relationships. However, it may not be necessary for some patients who have mild crowding or spacing, or when a limited treatment plan will not change the maxillomandibular relationship. For example, an adult with a chief complaint of mild crowding or spacing of the anterior teeth who requests limited treatment is unlikely to benefit from a cephalometric radiograph; taking this image is unlikely to change the treatment plan or the final outcome. Generally, when the incisor relationship does not require a significant change, a cephalometric radiograph is not required. Some studies have inferred that cephalometric radiographs do not significantly influence treatment decisions. In addition, there is no evidence to support the value of the cephalometric radiograph for predicting facial growth. Therefore, for some patients, if treatment decisions can explicitly be made without the cephalometric radiograph, and this image will not influence treatment decisions, the benefit to the patient becomes questionable, in which case cephalometric acquisition may be unnecessary.

Whereas panoramic and cephalometric radiographs in combination are sufficient for most patients, in some circumstances other imaging techniques should be considered: when more accuracy or information is needed, and when an object needs to be visualized in 3 dimensions. These examples support the contention that the same set of pretreatment radiographs should not be routinely prescribed for every patient. In these situations, other radiographic imaging techniques should be considered.

If more accuracy or information is needed, intraoral periapical radiographs should be considered because they are usually more accurate than panoramic radiographs for specific diagnostic tasks such as the evaluation of root resorption, root shape, and status of the alveolar bone. Periapical radiographs are also excellent for periodontal and caries diagnoses. The radiographic evaluation of periodontal status, incipient caries, and calculus deposits is best made from periapical and bitewing radiographs. Periapical radiographs will also show areas of bone loss, root anatomy, possible furcation involvements, apical radiolucencies, and widened periodontal ligaments. Therefore, when the panoramic radiograph is insufficient for evaluation of these findings, it can be supplemented with intraoral periapical radiographs.

Because the diagnosis of caries and periodontal disease is best made by periapical and bitewing radiographs, the orthodontist should not rule out incipient interproximal caries or alveolar bone loss by relying only on the panoramic radiograph, even if a high-quality image is available. It is always prudent to inform the patient or the parent that the checkup for carious lesions (or periodontal status) is best made and managed by the general dentist (or a periodontist) who will take intraoral radiographs as needed.

Initial radiographic acquisition in orthodontics

After reviewing the patient’s health history and completing a clinical examination, radiographs should be considered if they are likely to provide confirming or clarifying information that can affect the diagnosis and treatment. Because each patient is different, there is no indication for taking a standard or the same series of radiographs for all orthodontic patients.

To establish a comprehensive diagnosis for most orthodontic patients, case-specific radiographs are necessary for the patient’s benefit. With the ever-increasing quality of radiographic machines and images, the combination of pretreatment panoramic and cephalometric radiographs appears to be appropriate and sufficient in most cases.

For initiating orthodontic therapy, a panoramic radiograph has many advantages and provides much information, including the status of dental development. This single image provides an excellent and broad view of a variety of structures, including maxillary and mandibular dentitions, adjacent structures, and temporomandibular joints, and is quite helpful for patients with asymmetry. The panoramic radiograph is simple to obtain and easy to interpret and explain to patients.

Whereas a panoramic radiograph of good quality can show a significant amount of information, it comes with 3 main limitations. First, it lacks the fine detail required to diagnose and monitor carious lesions and periodontal status, and the objects outside the focal trough will not be shown in detail. Second, the panoramic radiograph is not dimensionally accurate and may include geometric distortion and unequal magnification throughout the image. Third, panoramic radiography requires the patient to be positioned accurately in the focal trough. To do so, it is valuable to follow the manufacturer’s recommendations for patient positioning, including the appropriate use of light beam markers. Staff members should be able to identify patient positioning errors and optimize the quality of patient positioning during panoramic radiography.

The value of the initial cephalometric radiograph, when appropriately acquired, should not be ignored. It can be useful for assessing growth and dental and skeletal relationships. However, it may not be necessary for some patients who have mild crowding or spacing, or when a limited treatment plan will not change the maxillomandibular relationship. For example, an adult with a chief complaint of mild crowding or spacing of the anterior teeth who requests limited treatment is unlikely to benefit from a cephalometric radiograph; taking this image is unlikely to change the treatment plan or the final outcome. Generally, when the incisor relationship does not require a significant change, a cephalometric radiograph is not required. Some studies have inferred that cephalometric radiographs do not significantly influence treatment decisions. In addition, there is no evidence to support the value of the cephalometric radiograph for predicting facial growth. Therefore, for some patients, if treatment decisions can explicitly be made without the cephalometric radiograph, and this image will not influence treatment decisions, the benefit to the patient becomes questionable, in which case cephalometric acquisition may be unnecessary.

Whereas panoramic and cephalometric radiographs in combination are sufficient for most patients, in some circumstances other imaging techniques should be considered: when more accuracy or information is needed, and when an object needs to be visualized in 3 dimensions. These examples support the contention that the same set of pretreatment radiographs should not be routinely prescribed for every patient. In these situations, other radiographic imaging techniques should be considered.

If more accuracy or information is needed, intraoral periapical radiographs should be considered because they are usually more accurate than panoramic radiographs for specific diagnostic tasks such as the evaluation of root resorption, root shape, and status of the alveolar bone. Periapical radiographs are also excellent for periodontal and caries diagnoses. The radiographic evaluation of periodontal status, incipient caries, and calculus deposits is best made from periapical and bitewing radiographs. Periapical radiographs will also show areas of bone loss, root anatomy, possible furcation involvements, apical radiolucencies, and widened periodontal ligaments. Therefore, when the panoramic radiograph is insufficient for evaluation of these findings, it can be supplemented with intraoral periapical radiographs.

Because the diagnosis of caries and periodontal disease is best made by periapical and bitewing radiographs, the orthodontist should not rule out incipient interproximal caries or alveolar bone loss by relying only on the panoramic radiograph, even if a high-quality image is available. It is always prudent to inform the patient or the parent that the checkup for carious lesions (or periodontal status) is best made and managed by the general dentist (or a periodontist) who will take intraoral radiographs as needed.

CBCT acquisition in orthodontics

If an object needs to be visualized in 3 dimensions or 2-dimensional (2D) imaging is insufficient for gathering necessary diagnostic data, CBCT imaging may be considered to improve diagnosis. It uses a 2D detector and a divergent and cone-shaped source of ionizing radiation; hence, its name. CBCT imaging can provide accurate submillimeter resolution images in 3 dimensions. These images serve a number of diagnostic purposes in orthodontics.

The acquisition of CBCT imaging can improve the diagnosis in selected orthodontic patients, by providing 3-dimensional evaluation of anomalies in dental position (impacted or ectopic teeth), dental structural anomalies, dentofacial deformities, airway insufficiencies, temporomandibular joints, and pathologies. CBCT can also be used to assess craniofacial anatomy, alveolar boundary conditions, maxillary transverse dimensions, vertical malocclusion, and obstructive sleep apnea. Advanced applications of CBCT imaging in craniofacial orthodontics include the evaluation of skeletal and soft tissue asymmetry, effects of expansion, and bone in a cleft site.

Furthermore, CBCT can alter treatment planning decisions, notably for patients with impacted maxillary canines, unerupted teeth with questionable locations or delayed eruption, severe root resorption, or severe skeletal discrepancy. Although the benefits of CBCT in orthodontics cannot be ignored, the orthodontist must be able to justify that CBCT images bring a benefit to the patient over what can be obtained via 2D imaging.

Despite the potential of CBCT to alter treatment planning decisions, some authors believe that CBCT does not necessarily improve the outcome of orthodontic treatment. In other words, although CBCT might improve diagnosis and influence treatment planning, the outcome in general may be similar or comparable if 2D radiographic imaging had been used. It is generally difficult to know the value of CBCT imaging in changing treatment outcomes because most of the evidence on its diagnostic performance and efficacy is based on observational studies or those with variable hierarchies of evidence.

Furthermore, for most CBCT examinations, the effective radiation doses are greater than those for conventional radiographic techniques. To estimate the stochastic health risk of any radiographic technique that uses ionizing radiation, a radiation protection quantity known as the effective dose is used. The effective dose is the sum of the equivalent doses to the organs and tissues exposed, multiplied by the risk-tissue weighting factors. The unit of measurement of the effective dose is the sievert, and it is frequently reported in dentistry as microsieverts (μSv). For reference, the average effective dose in the United States from the ubiquitous naturally occurring background radiation (eg, unavoidable environmental exposures such as radon gas and cosmic rays) is approximately 3000 μSv per year.

Table I presents effective doses of 2D imaging techniques vs those of CBCT. The effective dose of panoramic radiography is estimated to be 6 to 38 μSv ; the effective dose of cephalometric radiography is approximately 2 to 10 μSv, whereas the effective dose of an intraoral full-mouth series is approximately 34 to 388 μSv. On the other hand, the wide range of reported effective doses of CBCT acquisitions is 20 to 1025 μSv, which varies between different machines, fields of view, and certain technique factors. Most CBCT scanners use dosages that are within the lower half of this wide range. The high reported values are mostly for older CBCT units with variable settings. Additionally, these values for CBCT are relatively smaller than the effective doses of medical computed tomography head scans, which can be approximately 1000 to 2000 μSv.

One industry response to the concern about the long-term risks of CBCT in orthodontic patients resulted in offering low-exposure alternative scanning options in newer scanner models. This resulted is the availability of small-volume or quick-scan protocols with low radiation doses that rival those of panoramic and cephalometric radiographs. Some authors believe that this development would make the debate about the CBCT radiation dilemma a historical footnote. However, the recently developed quick scans use 180° rotation and result in lower resolution and reduction in image quality compared with standard or high-resolution protocols that use full 360° rotation. The decreased image quality in quick scans may render the image insufficient for specific diagnostic tasks. In addition, the quick scan or low-dose option features are not consistently available in many commercially available CBCT units, which still vary significantly in their radiation dosage ranges and image quality.

Also, the effective doses are averaged across all ages and for both sexes. At all ages, the stochastic health risks for female patients are slightly higher than those for males. More importantly, the theoretical risk of these doses is age-dependent—highest for children and smallest for elderly patients. Table II presents the age-risk relationship based on a 30-year-old adult. If the relative attributable lifetime risk based on a relative risk of 1 is given for the adult at 30 years of age, a patient at age 10 to 20 would have a 2-fold risk because the younger patient has more radiosensitive organs and a longer lifespan. On the other hand, a patient above 80 years of age has a negligible risk because the latent period between the radiographic exposure and the clinical presentation of a tumor formation will far exceed the patient’s lifespan. In other words, the cancer risk per unit dose of ionizing radiation is generally higher for younger patients than for adults.

The concept of the effective dose becomes more problematic when applied to young orthodontic patients exposed to CBCT, because 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 and their long life expectancy. Furthermore, with CBCT imaging, several radiosensitive organs receive higher organ and effective doses. This is especially true for small children, because the thyroid gland is closer to the field of view when imaged than that of an adult. Effective dose variations also depend on the child’s age. All exposure protocols being equal, a small 10-year-old patient would receive a 30% higher effective dose than an adolescent, because of the 10-year-old’s smaller size.

Due to these dilemmas, the evidence on the use of CBCT is inconsistent, including a wide variety of conflicting opinions. Some authors believe that despite the small increase in radiation dose relative to panoramic and cephalometric radiographs, the advantages of CBCT justify prescribing this image for every orthodontic patient. Others believe that the evidence for its efficacy is lacking, and some have questioned the ethics of prescribing CBCT for all orthodontic patients. Conducting randomized controlled trials has been recommended to provide an evidence-based approach for prescribing CBCT to prove whether it can result in a measurable and meaningful patient outcome.

At present, to aid clinicians in incorporating the strongest evidence into patient care regarding the use of CBCT, it is reasonable and prudent to follow clinical practice guidelines provided by respected dental organizations. These guidelines are defensible and are considered a robust source of evidence. The American Dental Association recommends that CBCT imaging in dentistry should be prescribed only when the diagnostic yield will benefit the patient or improve the clinical outcome significantly. The American Academy of Oral and Maxillofacial Radiology recommends that the use of CBCT imaging in orthodontics should be justified on an individual basis, according to the clinical presentation. Several international organizations have provided similar recommendations. The comprehensive and sensible British Orthodontic Society guidelines suggest that there is no indication for the routine use of CBCT imaging for all orthodontic patients. The Swiss Association of Dentomaxillofacial Radiology recommends that CBCT imaging in orthodontics is justified only if the expected additional information is therapeutically relevant, compared with conventional 2D imaging.

Therefore, if CBCT imaging would benefit the patient or change the outcome of treatment when compared with 2D radiographs (eg, panoramic and cephalometric), then its acquisition is justified. The converse is also true. Furthermore, taking a large field of view CBCT scan merely to synthesize a cephalometric image is not indicated, because a 2D cephalometric radiograph could have been prescribed without exposing the patient to the additional radiation. To do so would be at odds with the ALARA directive in radiation protection. It is also unjustified to take CBCT images to merely replace impressions or digital scans that do not use ionizing radiation or to obtain the status of a high-tech orthodontic practice.