We thank Dr Webb for his comments on our article (Abdelkarim A, Jerrold L. Clinical considerations and potential liability associated with the use of ionizing radiation in orthodontics. Am J Orthod Dentofacial Orthop 2018;154:15-25). Because his was a very detailed and well-supported opinion, we felt the need to respond in kind. As we mentioned in our original article, we must stress again that there are no legally binding statutes, rules, or regulations that provide explicit radiographic prescription protocols for orthodontic practice. However, there are guidelines for the appropriate and defensible use of ionizing radiation in orthodontics.
Regarding Dr Webb’s question about cone-beam computed tomography (CBCT), if a practitioner chooses to use CBCT scans for all radiographic acquisitions with effective radiation doses equal to or less than those for conventional 2-dimensional (2D) radiographic techniques, we are happy to provide an answer based on a holistic consideration of radiation physics, radiation biology, radiographic interpretation, digital imaging, risk management, quality control, and, of course, evidence-based practice.
As we discussed in our article, 1 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 that use low radiation doses that rival those of panoramic and cephalometric radiographs. Specifically, using the i-CAT FLX CBCT unit (Imaging Sciences, Hatfield, Pa) and selecting the QuickScan+ protocol and a large field of view (FOV) of 16 × 13 cm capable of synthesizing a cephalometric radiograph, the estimated effective dose would be only 11.4 μSv for an adult. This dose rivals the combined effective dose of panoramic and cephalometric radiographs. To be more accurate, the dose for a child should have been selected when asking this question because most orthodontic patients are children, but the estimated effective dose would still be low, at 17.5 μSv. So, the question here is whether an orthodontist can choose to use a large volume CBCT with QuickScan+ protocol for all radiographic acquisitions instead of taking 2D images. The premise of this question is that taking 1 large-volume QuickScan+ CBCT can provide panoramic and cephalometric views as well as the additional benefits of CBCT imaging. As we stated in our original article, we do not recommend this practice.
The best of 1 imaging technique cannot be compared with the worst of another. Both CBCT and 2D imaging techniques have pros and cons that must be objectively weighed against each other. If you want to use QuickScan+ protocol, there is a significant reduction in image quality. QuickScan+ protocol use a 180° rotation and result in lower resolution and reduction in image quality when compared with standard or high-resolution protocols that use a full 360° rotation. QuickScan+ exposure time is 2 seconds only and uses the lowest beam energy and milliamperes. This protocol should not be perceived as a replacement for 2D imaging for all orthodontic patients but, rather, to give clinicians a viable option for specific diagnostic tasks and clinical encounters.
Holding the FOV of 16 × 13 cm constant, the selection of the QuickScan+ protocol with the i-CAT FLX CBCT unit has an effective dose of 11.4 μSv for an adult; however, using the slightly better-quality protocol with higher-beam energy and milliamperes is called “QuickScan,” and it has an effective dose of 54.5 μSv. The next protocol is called “standard” and has an effective dose of 85.3 μSv for the same volume size, and the best protocol called “high resolution” has 171.1 μSv for the same volume size. These numbers do not compare favorably with the effective dose of panoramic radiography, which is estimated to be 6 to 38 μSv, and cephalometric radiography effective doses, which are approximately 2 to 10 μSv. As CBCT doses continue to be reduced, so do the doses of panoramic and cephalometric radiography, and most of their current doses are at the lower end of these reported ranges.
Increasing the diameter of the FOV results in a modest reduction in the contrast-to-noise ratio, which is undesirable for the sake of image quality. Increased contrast-to-noise ratio generally results in an improved image. When the voxel size and FOV are held constant, the contrast-to-noise changes when different protocols are used (QuickScan+, QuickScan, Standard) and the QuickScan+ protocol have the most undesirable contrast-to-noise changes.
Several efforts for selecting larger CBCT volumes in orthodontics appear to be made to replace 2D panoramic and cephalometric radiographs and synthesize them later from the CBCT volume. When taking a large-volume CBCT of 16 × 13 cm, one that can synthesize a cephalometric radiograph, high quality and acceptable resolution are desirable because landmark identification and reliable cephalometric analyses would otherwise be useless. Therefore, taking a large volume of 16 × 13 cm and selecting QuickScan+ (low dose of 11.4 μSv), which could produce less than ideal and unreliable cephalometric analysis merely to beat the combined dose of panoramic and cephalometric radiographs, is a flawed practice. Alternatively, taking a volume of 16 × 13 cm with the standard setting (85.3 μSv) or high resolution setting (171.1 μSv) merely to synthesize a reliable cephalometric image is not indicated either, 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 appropriate radiographic selection criteria and the ALARA directive in radiation protection.
To use CBCT in orthodontics appropriately, we must identify its benefits and the reasons for its use. It provides 3-dimensional evaluations of anomalies in dental positions, dental structural anomalies, dentofacial deformities, airway insufficiencies, temporomandibular joints, and pathologies. It is used to assess craniofacial anatomy, alveolar boundary conditions, maxillary transverse dimensions, vertical malocclusions, and obstructive sleep apnea. In craniofacial orthodontics, it is used for evaluation of skeletal and soft tissue asymmetry, effects of expansion, and bone on the cleft side. All of these applications require high-quality images. Therefore, we respectfully disagree with Dr Webb’s idea that “although high-resolution scans may be required for certain periodontic, endodontic, or oral surgical procedures, the quality of ULD CBCT scans is diagnostically acceptable for orthodontic purposes.” When needed, most CBCT applications in orthodontics require high resolution or at least standard acquisition protocols to truly benefit the patient and justify CBCT use. To opt for the lowest resolution would deprive the patient of the best of what CBCT can provide. This is especially true for the impacted or ectopic canine, the most common application of CBCT in orthodontics, in which the tooth and its relationship to adjacent structures must be determined accurately.
Because each patient is different, there is generally no indication for taking a standard or the same series of radiographs for all orthodontic patients. Therefore, an initial low-dose CBCT should not be considered a panacea for all patients. Also, for progress and final radiographic imaging, low-resolution CBCT scans can be inadequate, and 2D scans can occasionally be preferable. Even for 2D imaging, each imaging method has its strengths. For example, for the assessment of root resorption, intraoral periapical radiography is more reliable that panoramic radiography. For posttreatment radiography, it would not be a good risk management practice to acquire the lowest resolution CBCT scan that would not clearly record the status of the dentition (eg, presence or absence of external root resorption) and the periodontium after treatment.
Therefore, it is meaningless to deliberately select low-resolution CBCT protocols to the point of producing low-quality images that are inadequately diagnostic. The decreased image quality in quick scans may render the image insufficient for specific diagnostic tasks. To truly benefit from the 3D capabilities of the i-CAT FLX CBCT unit or any other CBCT unit, one must select a protocol that provides diagnostically acceptable images.
In addition to the potential limitations of the QuickScan+ setting in this machine, it is also valuable to mention that the quick scan option is not available in many commercial CBCT units, which vary significantly in their radiation dosage ranges and image quality. There are over 40 commercially available CBCT units in the market and several thousands of already installed units in dental offices, none of which will be disposed of soon.
As we discussed in our article, we recommend that clinicians should incorporate the strongest evidence into patient care regarding the use of CBCT, not based on in-vitro studies, expert opinions, or case reports but, rather, by following guidelines from respected dental organizations. These clinical guidelines include recommendations intended to optimize patient care that are formed by exhaustive systematic reviews of evidence and assessments of the benefits and harms of alternative care options. These guidelines are the most defensible when the worst happens to a clinician (eg, lawsuit, state board action).
The American Dental Association’s recommendations about CBCT imaging in dentistry are broad: it 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 guidelines for the use of CBCT in orthodontics are more specific, recommending that CBCT imaging in orthodontics should be justified on an individual basis, according to the clinical presentation.
As of 2018, not 1 national or international organization has recommended the routine use of CBCT for all orthodontic patients. The argument that the introduction of an i-CAT FLX unit and dosages published in 2013 by Ludlow and Walker will change the recommendations of organized dentistry is unsubstantiated. Most landmark studies by Dr Ludlow about CBCT dosages are cited in the 2013 position statement of the American Academy of Oral and Maxillofacial Radiology, and he was a member of the expert panel that prepared these guidelines. Other members of the expert panel that wrote the position statement included several authoritative orthodontists and oral and maxillofacial radiologists who completed an exhaustive and thorough review of the scientific literature on CBCT.
Furthermore, Dr Webb stated that “When considering the effective dose of other 2D imaging options, particularly if ectopic teeth are suspected, ULD CBCT should be considered the imaging option of choice,” and he cited 2 references to support this statement, one by Ludlow et al and another by Isaacson et al. However, nowhere throughout these references was this recommendation made, and this recommendation is in fact at odds with appropriate radiographic selection criteria.
First, with few exceptions in which the lateral incisor is tilted, a severe arch-space deficiency is noted, or where a bulge in the alveolar ridge is palpable, it is very difficult to predict an ectopic canine while performing a clinical examination. CBCT can alter treatment planning decisions for patients with impacted maxillary canines. However, an impacted canine in clinical practice is usually discovered after acquisition of a 2D image, usually a panoramic radiograph. Furthermore, the reference by Ludlow et al had no discussion about CBCT and merely suggested that the effective doses of common 2D intraoral and extraoral imaging techniques warrant reconsideration of means to reduce patients’ exposure. The second reference (British Orthodontic Society guidelines) recommended almost the contrary of what Dr Webb stated for the ectopic canine clinical encounter. For the ectopic canine, the British Orthodontic Society guidelines recommend taking at least 2D radiographs, permitting use of parallax, which may be achieved using 2 intraoral radiographs or 1 intraoral radiograph and a panoramic radiograph, and then considering whether this is sufficient to make a treatment plan; if yes, then no further imaging is needed, but if no, then a localized CBCT can be considered.
The 2015 guidelines by the British Orthodontic Society did not change based on the introduction of the i-CAT FLX machine and the 2013 publication of the low doses achievable with QuickScan+ protocols. Their 2015 guidelines suggest that there is no indication for the routine use of CBCT imaging for all orthodontic patients. This is an example in which the guidelines did not change as Dr Webb predicted. Other guidelines made by the British Orthodontic Society regarding CBCT include the following.
There is almost no evidence for the impact of CBCT on diagnosis and treatment planning in orthodontics apart from for the impacted maxillary canine.
Use the smallest FOV consistent with the diagnostic needs.
For most CBCT examinations, the effective doses are typically an order of magnitude greater than those for conventional radiographic techniques.
We agree that the interpretation of CBCT images should preferably become part of orthodontic residencies so that orthodontists can interpret them in house if they choose to, especially for small volumes. Larger volumes may create a challenge for some clinicians. Many radiologists argue that “the eye cannot see what the mind does not know.” The worst scenario can happen if someone with inadequate training in CBCT radiographic interpretation misinterprets data, misdiagnoses specific conditions, or renders inappropriate treatment. Oral and maxillofacial radiology is a recognized dental specialty. It is thus up to each orthodontist to determine whether to perform in-house radiographic interpretation or refer to a specialist for interpretation. We hope that the 12% of orthodontic programs that do not use CBCT will adopt this technology and prepare their residents to be able to use it appropriately.
Based on established guidelines, CBCT imaging should be considered when it is expected to yield a benefit to the patient or change the outcome of treatment over 2D radiographs. The status quo for decades has changed because, in addition to 2D imaging, we now have CBCT. However, it cannot be concluded that CBCT imaging should replace panoramic and cephalometric radiographs unless new randomized controlled trials (RCTs) prove that CBCT can result in a measurable and meaningful patient outcome. CBCT does not necessarily improve the outcome of orthodontic treatment. We have no RCTs that demonstrates that CBCT delivers a nicer smile or any tangible orthodontic patient outcome. Most of the evidence on its diagnostic performance and efficacy is based on observational studies or ones with variable hierarchies of evidence. RCTs are the gold standard in study designs for evaluating the effectiveness of interventions, and if we desire to investigate a measurable value and ability of CBCT to change treatment outcomes over 2D imaging modalities, we need findings of several RCTs on CBCT. Based on these RCTs, new guidelines could emerge that specifically state new directives, but as of now we must follow the most current guidelines.
∗ The viewpoints expressed are solely those of the author(s) and do not reflect those of the editor(s), publisher(s), or Association.
The author completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported.