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Straight Talk: Instruction on CBCT in Orthodontic Graduate Education James Mah, DDS, MSc, MRCD, DMSc

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Instruction on CBCT in Orthodontic Graduate Education
By James Mah DDS, MSc, MRCD, DMSc

Perhaps the most significant technology introduced to orthodontics in recent years is cone beam computed tomography (CBCT). The installation base of CBCT devices in U.S. dental offices has grown approximately 100 percent per year since 2005. Initial utilization was in university and research centers, followed by rapid penetration into private practices. Along with this rapid growth and utilization, concerns regarding the clinical need for CBCT in orthodontics, radiation dosimetry and knowledge to interpret the imaging data have emerged. From an academic perspective, a common issue facing many orthodontic programs is whether this technology should be included in the curriculum.

Does 3D imaging have a significant advantage compared to 2D? Here, we are reminded by the rich history of the orthodontic record, where pioneers such as Calvin Case used plaster models of the face and dentition to obtain a 3D record of the patient. Following the introduction of the cephalostat, Broadbent achieved multidimensional imaging with the use of two X-ray tubes oriented perpendicular to one another, which were simultaneously activated to produce lateral and postero-anterior cephalograms (PA ceph) which were registered to one another. However, since that time, the orthodontic record has been diluted, first by taking the lateral cephalogram and PA ceph separately, and second by steadfast reliance on the panoramic view. In the former, the PA ceph is often omitted from the patient record and when it is taken, is difficult to analyze and interpret because of issues relating to head position and anatomic superimposition. In the latter, while the panoramic is one of the most common views in dentistry, it is the most distorted and should be interpreted with extreme caution.

For assessment of tooth positions in orthodontics, all seven scientific papers on this topic conclude a panoramic is highly unreliable for the assessment of tooth tip and root parallelism. Yet this practice remains relatively common in orthodontic practices. Further, the orthodontic record consisting of a lateral cephalogram and panoramic is severely limited in the volume of information it provides and is lacking in the ability to reveal subtle asymmetries, dental details such as root anatomy and their torque, limitations of alveolar width, relation to soft tissue of the face, status of the temporomandibular joints, and sinuses and airways. It is foolish to think that CBCT imaging is only indicated if something is detected on the panoramic or lateral cephalogram since both these images lack diagnostic specificity and sensitivity compared to CBCT imaging. Given the clear advantages of CBCT imaging and potential benefit of detailed information to proper diagnosis and treatment planning, it is clearly the modality of choice for comprehensive orthodontics.

Radiation dosimetry, the second issue, is likely the most contentious and misunderstood aspect of CBCT imaging. There are scientific articles and professional organizations comparing dose data between conventional imaging versus CBCT and producing recommendations on clinical utilization of CBCT in orthodontics. However these decisions are largely made on unsound data. A systematic review of literature on the topic, from 1998 to 2008, analyzes 375 papers in detail, and shows there is lack of evidence-based data on the radiation dose for CBCT imaging.¹ These authors found that terminology and technical device properties were not consistent in the literature. Studies on radiation dosimetry in dentistry are largely not comparable due to variations in experimental methodology, different devices, machine settings, fields of view, dosimetry phantoms, calculations of effective dose (E) (E1990 vs. E2007 ICRP) and reporting of results. Radiation dosimetry from CBCT is within the range of conventional dental imaging (<100μSv) and far from that of medical CT (typically >10,000μSv). Further, these studies do not report the effect of patient shielding and variations in operational settings. In our research, we have found that by using a thyroid shield the dose to the patient is reduced by approximately 50 percent and if lower device settings are used, CBCT imaging can be performed with the same radiation dose to the patient as a panoramic image (5μSv). It is also important to note that daily exposure to X-rays from natural sources, mainly terrestrial and cosmic, is 8μSv. While an understanding of the deficiencies of the available information on dose is critical, consideration of radiation dosimetry and adherence to the ALARA principle remains important. The risk from imaging should be weighed against risks of missing information, and subsequent misdiagnosis and mistreatment to arrive at an overall risk:benefit determination for each patient.

The issue of image interpretation and responsibility for pathology that might be found on the images is a very common concern. This issue might be best resolved in a similar manner to others in dentistry. Users should have basic fundamental knowledge of anatomy, image display and interpretation with the judgment to refer to a specialist when indicated. To gain basic knowledge, it seems the best place to do so is alongside courses in anatomy, radiology, cephalometrics and pathology in the orthodontic curriculum. Graduates may obtain basic knowledge from attending continuing education courses dedicated to this subject matter. Inclusion of the oral and maxillofacial radiologist (OMFR) in the interdisciplinary team is akin to that of other specialists on the team. These individuals have unique training and special knowledge in radiology and pathology that could be of great assistance. On this topic, many of the malpractice insurers, including the AAOIC, strongly recommend utilization of OMFRs in the interpretation of CBCT data. If a clinician chooses to interpret the data on his or her own, they take on the responsibility to the same extent as the OMFR.

Lastly, the issue of whether to include CBCT imaging in orthodontic curricula remains. While CBCT imaging is not a Commission on Dental Accreditation program requirement, there has been discussion that it should be included if accessible. From an academic perspective, and after evaluation of the scientific literature, it is clear 2D records are lacking and the volume of information provided by CBCT imaging allows for a more comprehensive patient evaluation. The technology seems to be a lightning rod for dividing orthodontic programs into the more progressive ones versus the status quo. Some feel that conventional records are good enough and there is no need to change, while others embrace the technology. It is also an issue of best preparing and educating residents for future practices. Given the advances in technology in the world around us and in the orthodontic profession, it is very convincing to believe that the best technology users will become the best orthodontists.

References
1. De Vos W, Casselman J, Swennen GRJ. Cone-beam computerized tomography (CBCT) imaging of the oral and maxillofacial region: A systematic review of the literature. Int J Oral Maxillofac Surg 2009; 38: 609-625
Author’s Bio
James Mah, DDS, MSc, MRCD, DMSc, is an associate clinical professor at University of Southern California and University of Nevada, Las Vegas. He is the technology editor for the Journal of Clinical Orthodontics. Dr. Mah is a member of the Pacific Coast Society of Orthodontists; the International Association for Dental Research; and the World Federation of Orthodontists. His 3D work has been featured by various media outlets including the Los Angeles Times, The National Post, Tech TV and other magazines and journals. Mah is the recipient of numerous awards including the Moyers Symposium Edison Honor, University of Michigan (2002); the American Association of Orthodontists Foundation Corporate Center Award (2001); and the Cleft Palate Foundation Research Award (1998).
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