“To see is to know”
As “owners” of the craniofacial complex, orthodontists are interested in understanding patients’ anatomic truth, in addition to the 3D spatial relationship of various structures. Traditionally, 2-dimensional imaging such as panoramic films, lateral & frontal cephalometric x-rays even plaster models have been used as orthodontic records (Figure 1 & 2). The problem with this approach is that these diagnostic pieces do not correlate well with that anatomic truth or with each other and it’s easy to miss findings. 2D images are actually lying to us. These diagnostic pitfalls have been overcome by newer, better, and safer 3D technology known as Cone Beam Computerized Tomography (CBCT). It is gradually becoming the industry standard, at least in modern offices. CBCT offers the ability to capture the head volume of the patient in a single scan using, relatively speaking, very low levels of radiation exposure1. Relatively speaking, because comparing apples to apples, if used correctly with the appropriate settings on newer generation machines, the radiation exposure of CBCT is actually less than the series of 2-dimensional x-rays currently used by most orthodontist 2, 3, 4, 5.
Cone Beam Computerized Tomography (CBCT), also known as Cone Beam Volumetric Tomography (CBVT), offers many significant practical advantages over older generation 2D imaging technologies. First of all, it captures the patient in their actual anatomically truthful, non-distorted form (Figure 3). Patients are, after all, three dimensional, and it would seem obvious that every orthodontist now should view them accordingly. CBCT is forcing us to see our patients in a different light now, more comprehensively and more holistically. CBCT offers increased clarity of three dimensional structures leading to improved diagnosis, treatment planning, predictability, and eventually better and faster outcomes. Doctors can be more educated about their patients’ conditions, therefore so can the patients. There is less guessing and more knowing, leading to less surprises and greater predictability of treatment outcomes. Much more than just a pretty picture, CBCT offers information never before available on 2D imaging such as TMJ status, information on the 3rd plane of space (depth), information about width of bone, bone & gum health, sinus health, palatal anatomy and the most important of all: the human airway (Figure 4).
Breathing is the foundation of life. Breathing is also a function of anatomy…of craniofacial anatomy. CBCT offers crystal clear visualization of airways and the surrounding craniofacial structures which influence airways such as jaw bones, palates, sinuses, facial relationships, adenoids, tonsils and more. This airway visualization issue is an absolute game-changer not only in orthodontics but in medicine because in view of the new crisis in healthcare known as Obstructive Sleep Apnea (OSA) (http://www.airwaydevelopment.com/2014/01/blog/), it is now the absolute responsibility and obligation of every orthodontist to screen, understand, manage and treat airway related problems and identify areas of obstruction (Figure 4). In fact not only should orthodontists consider the airways in orthodontic treatment planning, but actually plan every treatment around it for the prevention of future OSA in the adult years. Future articles on this blog will explore this new and fascinating relationship (http://www.airwaydevelopment.com/ ).
Of course benefits are one side of the story. But what about the risks and safety considerations? Any responsible clinician will be well informed about the latest scientific research and follow the principles of ALAR (As Low As Reasonably Achievable) which recommends using as little radiation possible to answer the clinical question. As with any intelligent discussion regarding healthcare pros and cons, one must follow what is known in medicine as Evidence Based Protocols (EBP) or Evidence Based Decision (EBD) making. The study of radiation absorption by the body is called “dosimetry”. Dosimetry is measured in units called Sieverts (Sv) or microSieverts (µSv). There are several world authorities on the issue of dosimetry in dentistry and medicine which have issued safety guidelines and recommendations. One of them is the International Commission on Radiological Protection (ICRP). The ICRP is considered an international public watchdog group made up of scientific experts around the world. They have recommended an annual radiation exposure safety limit of 1000µSv/pt/yr for medical diagnostic imaging5. The American Association of Physicists in Medicine (AAPM), an even more specialized group, has issued the following position statement (http://www.aapm.org/org/policies/details.asp?id=318&type=PP¤t=true) : “Risks of medical imaging at effective doses below 50,000µSv for single procedures or 100,000µSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged. These predictions are harmful because they lead to sensationalistic articles in the public media that cause some patients and parents to refuse medical imaging procedures, placing them at substantial risk by not receiving the clinical benefits of the prescribed procedures”6. Finally, The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report of 2012 states that no discernible effects of exposures below 100,000 µSv appear to exist, which is compatible with known cellular-repair mechanisms”7.
The future has arrived. Earlier this year, i-CAT Corporation released the iCAT FLX, yet another improvement in their generation of machines making Cone Beam CT technology better and safer. This machine produces full head size (16x13cm) volumetric scan at a dosimetry level (11 µSv) as low as half of a panorex (24 µSv8). This machine actually produces less radiation than a 2D x-ray according to a recent study appearing in the December issue of 2013 of the American Journal of Orthodontics and Dentofacial Orthopedics (AJODO)8. These levels were confirmed by independent academic institution based study by John Ludlow at the University of North Carolina who measured the dosimetry levels of the new iCAT FLX machine8. To give you an idea of how low this is, a digital panorex is about 24µSv in similar studies2. The implications of this in orthodontics and even pediatric dentistry are enormous. There are still CBCT machines out there that deliver over 500µSv, so clearly, CBCT dose varies substantially depending on what machine and what parameters are used. As a reference we are exposed to about 8-10µSv/day of radiation just being alive in a metropolitan place at sea level, such as Miami. A transcontinental flight from Miami to Los Angeles? About 50µSv. CBCT is rapidly becoming the new standard of care in orthodontics as it is better and safer than 2 dimensional x-rays.
- The Truth about CBCT Radiation. Sean Carlson, DMD, MS; John Graham, DDS, MD; William E. Harrell Jr., DMD; Edward Y. Lin, DDS, MS; Aaron Molen, DDS, MS and Wm. Randol Womack, DDS. Orthotown, Sept 2011, pg 62-68
- JB Ludlow, LE Davies-Ludlow, and SL Brooks. Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit. Dentomaxillofac Radiol July 2003 32: 229-234
- Daniel Ngan, Om Kharbanda, Joseph Geenty, M. Ali Darendeliler. Comparison of radiation levels from computed tomography and conventional dental radiographs Aust Orthod J. 2003;19:67-7
- Stuart C. White John B. Ludlow, Laura E. Davies-Ludlow Patient risk related to common dental radiographic examinations: the impact of 2007 International Commission on Radiological Protection recommendations regarding dose calculation. J Am Dent Assoc 2008;139;1237-1243
- ICRP Publication 103. The 2007 Recommendations of the International Commission on Radiological Protection.
- AAPM Position Statement on Radiation Risks from Medical Imaging Procedures. American Association of Physicists in Medicine (AAPM). December 13, 2011. http://www.aapm.org/org/policies/details.asp?id=318&type=PP¤t=true
- Bertin, D. M. [2012 report of UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation)]. 1–21 (2012).
- Ludlow, J. B. & Walker, C. Assessment of phantom dosimetry and image quality of i-CAT FLX cone-beam computed tomography. Am J Orthod Dentofacial Orthop 144, 802–817 (2013