Dr. David Gane interviews Dr. James Mah about 3-D imaging

June 1, 2010
The lateral cephalogram has long been the image of choice for orthodontic diagnosis and treatment planning.

By David Gane, DDS

For more on this topic, go to www.dentaleconomics.com and search using the following key words: CBCT, 3-D imaging technologies, model scanners, Dr. David Gane, Dr. James Mah.

Gane: The lateral cephalogram has long been the image of choice for orthodontic diagnosis and treatment planning. With the advent of 3-D imaging technologies, including cone beam computed tomography (CBCT), this could soon change. CBCT has proven very useful in orthodontics in the comprehensive assessment of the patient. To help us better understand the issues surrounding CBCT use in orthodontics, I recently posed the following questions to orthodontist and recognized 3-D imaging expert Dr. James Mah.

Gane: How long have you been using CBCT, and what are your selection criteria for its use?

Mah: I’ve used CBCT since 2002. Initially, I thought its use would be limited to localization of impactions, but after discovering that the volume also contained many key anatomical regions, I began to view the TM joints, sinuses, and alveolar ridges. The comprehensive nature of the dataset was a paradigm shift for me as I realized this remarkable technology provided a coherent and undistorted view of the patient. My selection criteria for CBCT are straightforward. If the clinical indicators call for comprehensive orthodontic care, I use CBCT as part of a thorough and comprehensive examination.

Gane: How do you use CBCT in your practice — for initial assessment only or do you include progress and/or final records?

Mah: Our initial records are photos and CBCT. We no longer take study models except for surgical and TMJ cases and patients with extensive metallic restorations. CBCT is unique in its ability to reveal patient issues and potential problems prior to treatment. This allows me a more comprehensive understanding of the patient’s situation, often shedding light on the etiology of the malocclusion.

I can then better derive my diagnosis and design a patient-specific treatment plan. Our progress CBCT scans are collimated and obtained with parameters that are optimized to manage dose. Our final records include CBCT examination, which allows for superimposition of pre- and post-treatment scans for better visualizing and quantification of treatment outcomes.

Gane: Do you charge an additional fee for CBCT imaging or is it included in the treatment fee? Is there any reimbursement from third-party payers for CBCT imaging?

Mah: We integrate the cost of imaging in the treatment fee since we believe it is part of comprehensive care. Although there are ADA codes for CBCT related procedures, I haven’t seen great success in patient reimbursement.

Gane: What are the attitudes of your patients toward CBCT imaging?

Mah: Patients are extremely positive regarding 3-D imaging. I’ve never met a patient who said, “No thanks, I’ll settle for 2-D.” Indeed, we conducted a survey of over 100 patients and learned that they think more of a dentist who uses 3-D imaging and are willing to pay more for the service. I’ve never had a patient concerned with the dose.

Gane: There has been much discussion about the potential risks of ionizing radiation. Can you explain how dose differs between CBCT and the more traditional 2-D orthodontic radiographic assessment? Is there an increased patient risk when using CBCT?

Mah: In most discussions I don’t think risk/benefit is addressed very well. Certainly there are risks from X-rays, but we have to remember that diagnostic imaging is essential to modern health care and X-rays are naturally occurring; there’s no way to avoid them. Fortunately, X-ray exposure from dental imaging is very low, typically in the range of less than one to several days’ of natural exposure.

This is in sharp contrast to medical CT where the exposure can be equivalent to many months of natural X-ray exposure. Additionally, traditional 2-D orthodontic records typically involve a few images resulting in total exposure at about the same level, or even higher, than CBCT imaging if an FMS is included.

While there is additional X-ray exposure to the patient, the risk to the patient if an issue or problem is not adequately detected is not well described. While there is abundant literature on the shortcomings of lateral cephalograms and panoramic imaging in orthodontics, the profession is short on reports on complications in orthodontics due to inadequate imaging.

Gane: Describe the process you use for reviewing the 3-D data. What are the professional responsibilities of obtaining a CBCT volume?

Mah: I review and write a report on every CBCT volume in a comprehensive manner — viewing the osseous structures of the skeleton, the TM joints, sinuses, airways, and dentition. However, not all clinicians have the training or experience to do this. As far as professional responsibility, the law is clear in this area. The dentist is responsible for interpretation of dental images, whether 2-D or 3-D.

Fortunately, there are oral and maxillofacial radiologists available to assist. They should be part of the interdisciplinary team just like any other dental specialist.

Gane: How can one receive a second opinion written radiology report, and what learning resources are available for those who would like to learn more on visualizing and analyzing CBCT data?

Mah: There are oral radiological services available at very reasonable costs. Typically these services take a report request from the dentist and a radiology report is returned electronically. Many of the report requests are for a review of incidental pathology, but additional services such as nerve marking and implant planning are also available.

There are a number of continuing education courses available to learn the basics of CBCT data management and interpretation. Indeed, we are conducting a certification course for CBCT users July 16 and 17 at the University of Nevada, Las Vegas.

Gane: There are a number of CBCT systems marketed for orthodontic use. Some are dedicated CBCT systems, and others are hybrid systems combining CBCT with digital panoramic and cephalometric capabilities. Which is the more appropriate technology for orthodontic use?

Mah: It is always good to have choices to match the philosophy of the orthodontist and his or her imaging goals. Small field of view (FOV) systems are typically coupled with a panoramic and lateral ceph device to provide an “all-in-one” device such as the Kodak 9000C 3-D and the Suni3-D 3 in 1. Small FOV CBCT is used to further investigate a defined region such as impacted teeth and single TMJs. Advantages of a small FOV include lower dose and less potential for incidental pathology.

Larger FOV is advantageous because it includes the entire region of interest for assessments of craniofacial dysmorphology, sinuses and airways, certain pathologies, and a view that includes both TMJs. You will find that both small and large FOV devices match the working philosophy of the orthodontist.

Gane: How can CBCT guide orthodontic treatment? What is SureSmile?

Mah: Aside from the obvious assessments of skeletal and dental malocclusion, CBCT offers advantages for biomechanical planning in 3-D. I believe the orthodontist should view tooth movement in much the same way as a dentist placing implants. The 3-D tooth positions can be determined along with limits of tooth movement.

Specifically, alveolar bone height and width need to be considered. In this regard, the OraMetrix SureSmile process fits well. In this process, either a direct oral video scan or a CBCT scan is used to produce a dimensionally accurate 3-D model of the dentition, which is used for diagnosis and biomechanical planning. The process includes robotic formed archwires to implement the planned tooth movements.

Gane: In addition to CBCT we are seeing other 3-D imaging systems for orthodontic use, such as 3-D photographic systems and model scanners. How long can it be until fusion of these data sets gives us a virtual dental patient?

Mah: 3-D photographic systems are available from several manufacturers but these typically remain in research and university environments. An interesting approach is to “wrap” a 2-D facial photograph onto the CBCT volume. 3-D models can be obtained using direct scan systems such as 3M’s Lava Chairside Oral Scanner, Orametrix’s Orascanner, and Cadent’s i-Tero. Already we are seeing fusion of these high resolution dental models into the CBCT volume. This capability can be found in Materialise’s OMS software for craniofacial and orthognathic surgical planning.

Gane: What about the fourth dimension? When can we expect that to arrive?

Mah: In 2003, my laboratory created the Virtual Dental Patient, which incorporated mandible position and movement data from ultrasonic jaw motion tracking. Since then there has been development of camera and LED-based systems to provide the motion data. While the technologies are available and the capabilities exist to incorporate this data, the interest is just peaking for clinicians. At this time, Anatomage’s in-vivo modeling module does provide simulations of mandibular movement.

Dr. James Mah is an associate clinical professor at the University of Southern California and the University of Nevada, Las Vegas. At USC, he is the director of Redmond Imaging Center and the director of the Craniofacial Virtual Reality Laboratory. He may be reached at [email protected].

Dr. David Gane has a long-standing passion for dental imaging, and has published and lectured nationally and internationally on the topic. He serves as vice president of dental imaging for PracticeWorks, the exclusive maker of Kodak Dental Systems. Reach him at [email protected].

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