New technology often enables us to do things better or more efficiently than we could before. Many of us are eager to embrace the potential of the latest tool placed in our hands. As dental professionals, however, we have been taught to resist the temptation of the glossy brochures and promises of salespeople and to use our best judgement when considering the application of new technology to our practice. We must consider how our patients will benefit, how the new instrument compares to other available methods and how our practices profit in terms of efficiency and economy. Cone Beam computed tomography (CBCT) is an example of such a new technology and some of the factors involved in deciding to adopt the use of CBCT in our practices are discussed here.
CBCT is the newest modality available for imaging the maxillofacial region. It is a powerful instrument that can provide radiographicimages through any plane of the jaws as well as three-dimensional reconstructions. This ability to view the anatomy from limitless perspectives has not been readily available to the dental profession in the past and has great diagnostic implications. Dentists planning implants for patients can now clearly visualize the buccal and lingual dimensions and contours of the alveolar ridges, which can only be completely assessed by cross-sectional imaging. Vital anatomic structures, such as the inferior alveolar nerve canal, maxillary sinuses and bony fossae, can be localized with great accuracy and the internal bone pattern can be appreciated. The osseous structures of the temporomandibular joints can be studied and impacted teeth can be localized with respect to adjacent teeth or vital structures. These are just a few examples of the uses for which CBCT is being adopted.
There are many additional positive features of CBCT: The acquisition of a CBCT scan is quick and convenient for patients; high spatial resolution allows good assessment of bony details; and relative to medical computed tomography (CT), the only way, previously, to get the multiplanar imaging that is so beneficial to diagnosis, the radiation dose received by patients is much lower. 1 There are limitations, though, to this technology that must be recognized: The dose from CBCT is still greater than that received by conventional imaging methods, such as intraoral or panoramic techniques; soft tissues of the head and neck are not distin- guished due to low contrast resolution; and metal within the imaged field, most commonly from dental restorations, create artifacts that cause regional degradation of the image.
There is no doubt, that when applied appropriately, CBCT has the potential to benefit dental patients. So, why then is there concern about the use of this modality that has resulted in regulation of its use in the province of Ontario as well as in other jurisdictions? This is because some governments or regulators consider CBCT to be more complex than other dental imaging modalities and have concerns for patient safety if it is misused. Three major factors can be considered to be required for the appropriate use of CBCT; appropriate application of the modality, appropriate image acquisition protocoling and appropriate handling of the acquired data set.
As with all radiographic procedures, CBCT is a diagnostic test. Application of a diagnostic test requires that a risk vs. benefit assessment be done. This is because a patient should only be subjected to a test for which he or she can expect to receive a benefit that outweighs the risk involved. The benefit to the patient is to confirm or refute a working diagnosis or to guide a proposed treatment plan. Determining if a patient will benefit from a CBCT examination requires an understanding of the applications for which CBCT is proven to be valuable; assessment of potential implant placement sites is, while diagnosis of caries is not, for example. Making the risk vs. benefit assessment also requires an understanding of the dose and biologic effect resulting from the radiation exposure. Although the radiation dose imparted in diagnostic imaging is generally considered to be minimal, the risk estimates are not zero and therefore we must adhere to the principle of keeping patient exposures as low as reasonably achievable (ALARA). The European SEDENTEXCT project group has produced comprehensive evidence-based Provisional Guidelines on Cone Beam CT use which can be accessed at www. sedentexct. eu/guidelines.
To highlight a more controversial application, CBCT has been rapidly adopted for the use of orthodontic treatment planning in many centers. Although there are cases where the information obtained from CBCT will indeed benefit the patient (skeletal asymmetry, impacted teeth, for example) there are concerns that a risk vs. benefit assessment does not justify the routine use of this modality for all orthodontic cases: The benefit received is questionable, since other, lower dose, means exist to do the necessary evaluation; the risk is increased because the dose is higher due to the large field of view which is needed to capture the necessary anatomy while, moreover, the young population that most commonly undergoes orthodontic treatment is more sensitive to the radiation exposure.
Further, there is a concern that if practitioners who prescribe CBCT are also owners of the equipment, then a risk of overuse arises. In the setting of self-referral, a potential for less conservative application and therefore a conflict of interest, exists. It has been shown that practitioners who own panoramic machines prescribe this examination with greater frequency. 2 This might seem to be an obvious and trivial statement; however, it suggests the possibility of overuse where practitioners may be considering the economic benefit to the practice more than the diagnostic benefit to the patient. An analogous situation could be expected with CBCT. Unfortunately, potential negative outcomes occurring when radiographic procedures are over-prescribed are inconspicuous compared to more apparent effects of other unsuccessful procedures. This potentially leaves the population bearing an unaccountable risk.
When it has been determined that a CBCT scan is required, the next step is determining the appropriate protocol for image acquisition. Several factors must be considered in order to optimize image quality while minimizing patient exposure, including selecting the field of view and resolution and setting the exposure parameters. The practitioner must have an understanding of how each setting affects the characteristics of the acquired images. Each CBCT manufacturer has different available options and, though it may seem to simplify the procedure, a “one size fits all” approach is not the appropriate solution.
Finally, when a scan volume has been obtained, the diagnostic task that necessitated the CBCT scan must be appropriately addressed. It is necessary that the practitioner have the skills to manipulate the data set and software tools in order to obtain meaningful and accurate results. The responsibility of the practitioner does not end there, how- ever. As with any other radiographic examination, the entire imaged volume must be read. With a panoramic radiograph, this means that, although the reason for the image to be taken may have been to assess the third molars, it is the obligation of the clinician to read all parts of the film. With CBCT, every part of the patient’s anatomy that is depicted in the study must be assessed for abnormalities. For larger size fields of view, this may include the structures of the orbits and skull base to the cervical spine and larynx. The practitioner must be able to distinguish normal from abnormal findings and identify when abnormalities would require further investigation. A patient cannot release a practitioner from this responsibility. If a clinician cannot perform this task then they are obliged to seek the expertise of someone who can.
CBCT is a wonderful new technology with many potential applications that benef
it our dental patients. As with any new technique, however, we must proceed with professional and evidence-based judgement. Given the complexity of this modality and the many factors involved in its appropriate use, it just might be that regulations are the best way to achieve this and ensure that the well-being of our patients remain our primary concern.
OH
Dr. Perschbacher is an Oral and Maxillofacial Radiologist and a member of the editorial board of Oral Health. She is an Assistant Professor at the Faculty of Dentistry at the University of Toronto, where she teaches in the undergraduate and graduate radiology programs. She also practices Oral Radiology in a private practice in Toronto.
Oral Health welcomes this original Viewpoint.
REFERENCES
1. Ludlow JB, Ivanovic M. Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology. Oral Surg Oral Med Oral Path Oral Radiol Endod 2008;106:106-114.
2. Bohay RN, Stephens RG, Kogon SL. Survey of radiographic practices of general dentists for the dentate adult patient. Oral Surg Oral Med Oral Path Oral Radiol Endod 1995;79:526-531.
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There are limitations, though, to this technology that must be recognized
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It is necessary that the practitioner have the skills to manipulate the data set and software tools to obtain meaningful and accurate results
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With CBCT, every part of the patient’s anatomy that is depicted in the study must be assessed for abnormalities
