reading

Rev. ed. of: Color atlas of cone beam volumetric imaging for dental applications / Dale A. Miles. c2008.

I. Miles, Dale A. Color atlas of cone beam volumetric imaging for dental applications. II. Title.

[DNLM: 1. Stomatognathic Diseases--radiography--Atlases. 2. Cone-Beam Computed Tomography--methods--Atlases. WN 17]

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I am overwhelmed and somewhat humbled by the unexpected success of the first edition of this atlas. I am also deeply grateful to the many colleagues who have approached me at seminars to tell me that they keep this book beside them when they are examining their cone beam volumes as well as to the many others who have asked me to sign their copy of the first edition. Obviously, the book has made an impact in this exciting new era of oral and maxillofacial radiology.

In this updated second edition, I have used the term cone beam computed tomography (CBCT) instead of cone beam volumetric imaging (CBVI). I still believe that the more correct term for this modality is volumetric imaging. However, as most of my radiology colleagues have pointed out, the term CBCT is ensconced in the dental and medical literature, so I have decided, somewhat reluctantly, to adopt the term myself. In addition to the minor title change, I have added new cases to most chapters, developed a new section to address anatomy in the small volume, and added three new chapters to discuss applications for CBCT in endodontics, the risks and liabilities of CBCT, and selected cases from my radiology practice. I believe that these additions and updates have strengthened the book and made it even more useful.

I am smart enough to know my limitations, and in this edition, I have invited my first contributor, Dr Thomas McClammy*, a great endodontist and a great friend. He has written chapter 16 about the use of CBCT in the specialty of endodontics. As an early adopter, Dr McClammy did his due diligence, agonized over the decision to purchase a CBCT machine, and then plunged in. He has been like a kid in the proverbial candy store, and his enthusiasm about this modality comes through as he explains its incredible utility in his practice of endodontics.

Finally, some readers may question a radiologist attempting to address liability issues arising from the use of CBCT. However, I feel very strongly that some colleagues are setting themselves up for legal action by persisting in looking at the CBCT volumes only to determine a suitable implant site, and by neglecting the examination of the rest of the data or its referral to a specialist. This is the profession’s standard of care when a task or diagnosis is beyond our capability. Most of what I state in chapter 17 is common sense. Nevertheless, I am taking this risk myself by addressing this concern directly. I do it for my own peace of mind and to educate my colleagues.

I know the reader of this second edition will see these developments in the book’s content as both necessary and exciting. Enjoy, and thanks again for the support.

Like any innovation in the dental profession, the availability of cone beam volumetric imaging (CBVI) has preceded the understanding of its use. It happened with panoramic imaging as it did with digital radiographic imaging. The cone beam images in this atlas will educate dental professionals on how to use CBVI technology to better visualize the diseases and disorders that they encounter with their patients.

One aim of this atlas is to refresh the reader’s memory of anatomy. As dentists we never “worked” in the axial plane of section after our anatomy training; we have lived our lives in a world of plain films or digital images, all in the format of 2D grayscale panoramic, intraoral, or lateral cephalometric images. CBVI allows us to visualize patient anatomy and pathology like never before. CBVI helps to reveal bony changes caused by pathology. In addition, the level of anatomic detail in the 3D image sets means that clinicians placing implants no longer have to experience anxiety about whether they are placed correctly. CBVI allows us to determine the precise location of the inferior alveolar nerve in relation to impacted mandibular third molars, which improves preoperative planning and reduces patient morbidity as well as our liability. At last, we can see out patients’ problems in a whole new manner—in 3D and color. I hope this book will help you understand how CBVI can improve your clinical experiences and the management of your patients’ treatment.

I am deeply appreciative to CyberMed USA and CyberMed International for allowing me to continue to test their software product and to use it in my practice. I happen to think that it is the premier software for examining cone beam computed tomography image data. Mr Eusoon Han and the marketing team at CyberMed USA work tirelessly to support the product and have helped me understand the incredible tools within the software. Thanks to all. Thanks once more to Prof C. Young Kim, the CEO of CyberMed International for your product, your confidence, and your friendship. This book would not be possible without your product and support.

A big thank you to Mr William Hartman of Quintessence for going the extra mile with my requests, and to Ms Lisa Bywaters and Ms Bryn Grisham for their editorial support.

Finally, love and special thanks to my wife, Kathryn, for her continued support, love, confidence, sacrifice, and patience.

Nothing has captured the dental profession’s imagination in the past few years like the introduction of cone beam volumetric imaging (CBVI), which is now referred to by most clinicians and even in the literature as cone beam computed tomography (CBCT). I too now refer to the data volumes I receive from clients as CBCT volumes, despite my opinion that CBCT images bear no resemblance to traditional medical computed tomography (CT) scans except in the display of the final product.

The process of image acquisition for CBCT machines is unlike traditional medical CT scanners in that the patient is not usually supine, the image gathered is in a voxel (volume element) format, the x-ray dose absorbed by the patient is substantially lower, appointment availability is much easier, and it is less expensive. In short, although this imaging modality produces signicant data volumes like medical CT, it is different and vastly superior to traditional CT data for specic dental applications.

Dentists and dental specialists continue to be amazed at the incredibly precise and profound information produced by CBCT scans, and they are realizing that the data they receive will influence their treatment decisions like no other imaging modality used in the profession in the past 100 years. CBCT makes clinical decision making easier and more precise, patient treatment decisions more accurate, and visualization of the x-ray data more meaningful. Dentistry is moving away from “radiographic interpretation” and into “disease visualization,” and it could not have come at a better time.

Clinical Applications of CBCT

The applications for CBCT encompass most of the procedures clinicians perform in their office. Some applications for CBCT are listed in Box 1-1; examples of many of these applications are discussed in chapters 4 to 16. Additional applications will undoubtedly follow as clinicians learn about and begin to appreciate the incredibly beneficial data this imaging modality delivers for improved treatment planning and clinical decision making.

The evolution of implant technology, the technical skills and training of dental professionals, and the patients’ desire for more permanent and predictable restorative solutions to missing teeth all ensure that implant dentistry will remain the largest growth market for dental professionals and commercial vendors for at least another decade. Within 5 years, the reconstructed data in 2D/3D grayscale and color formats from CBCT machines will become the standard of care for displaying patients’ radiographic information for presurgical implant site assessment, implant placement, and follow-up radiographic assessment. CT, plain film imaging, and digital imaging modalities will probably become obsolete, at least for implant dentistry applications.

In recent years, the most rapid adoption of CBCT technology has been in the endodontic community. Manufacturers of limited field of vision (FOV) units have rigorously pursued the use of CBCT for endodontic imaging. In addition, a position statement on the use of CBCT in endodontics was developed jointly by the American Association of Endodontists (AAE) and the American Academy of Oral and Maxillofacial Radiology (AAOMR) and published in 2011.^1,2 More clinicians are discovering that CBCT data provides tremendous advantages with its thin slices and precision in endodontic imaging. For this application alone, sales of limited FOV machines will continue to increase.

Another growing area for CBCT application is in the diagnosis and treatment of obstructive sleep apnea (OSA). CBCT provides precision airway assessment that can quantify the amount of airway opening as well as the effects of different intraoral appliances. Treatment of OSA improves patient quality of life while reducing the risk of cardiac complications related to having an obstructed airway. This application of CBCT allows clinicians to significantly improve patient systemic health. Construction of simple intraoral appliances are essential for patients who have failed with continuous positive airway pressure (CPAP) machines and have increased cardiac risk.

Considerations for CBCT

The rapid rate of adoption of this technology has been surprising. By the summer of 2011, I had interpreted over 10,000 CBCT scans and the first edition of this book was already out of print. Now I spend close to 80% of my professional time interpreting CBCT scans and creating reports for clinicians who use this technology. I practice my specialty of oral and maxillofacial radiology both from my home in a dedicated radiology office environment as well as while I travel to give lectures and consult. I can operate just as my medical radiology colleagues do and practice my specialty from virtually anywhere in the world because of global Internet access.

Just as there are many different CBCT models available on the market, I receive the data volumes to interpret through many different avenues. Gone are the days when we relied on 2D grayscale single images attempting to represent 3D structures, viewed on light boxes under poor lighting conditions, to help us make our clinical treatment decisions. It is now possible to have 2D and 3D color “renderings” of each patient’s anatomy and signs of clinical diseases/disorders.

Figure 1-1 shows this CBCT machine’s broad capabilities and power. Whether you are considering purchase of a machine for image acquisition in your practice or simply accessing this technology by requesting a scan, you should consider the following important questions:

The data volume vs the single image

Before I address these questions, it is very important to understand the size difference between a data volume from a CBCT machine and traditional static 2D grayscale images. Each periapical image in a computer is about 300 kB in size, and three of these static intraoral images would fill a 1-MB floppy disk. A digital panoramic image is about 5 to 7 MB, so approximately 100 images could fit on a CD-ROM. By contrast, each CBCT data volume acquired for a single patient can range from 100 to 250 MB. Only a few patient scans would fit on an 800-MB CD-ROM. Even the so-called small-volume machines provide much more anatomical information than we have been accustomed to viewing and assessing (Fig 1-2).

Fig 1-2 Small-volume 3D color reconstruction of a 9-year-old patient with a fractured mandible, rendered with Accurex (CyberMed International). The fracture is easily identified in the anteroposterior view, and the 3D image can be rotated 360 degrees to see the fracture in any orientation.

The impact of this data volume is huge, both literally and figuratively. Several large-capacity computers or servers are necessary to store the volumes. These data volumes should also be stored offsite via the Internet, which requires high-speed Internet connection.

In addition, as a clinician, remember that you are responsible for all of the information in a volume, whether you order or acquire it, and whether it is for your own use or for a referral client. This tenet is still a source of confusion within the profession and is sometimes made more confusing by conflicting information provided by CBCT scanner manufacturers.

Chapter 16 is new to this edition and discusses the risk and liability issues specific to CBCT volume data. The chapter is illustrated with multiple examples of occult findings from volume data that, if missed, would have led to patient harm and delayed treatment. Such oversights are unacceptable in the dental profession, which has an implicit responsibility, like the medical profession, to do no harm. No clinician can have a patient sign a form absolving him/her from this important duty.

The responsibility for looking at the entire data volume is analogous to looking at a single panoramic radiograph. No clinician would look at only half of a panoramic radiograph; clinicians must look at the entire image. CBCT data, although much more extensive, is no different, and if a clinician cannot interpret the entire volume, referral to a specialist who can is necessary. Although this at first seems to represent a fundamental paradigm shift for all clinicians, it is really common sense and the standard of care that we would use for any specialist referral. When a clinician is in doubt about a finding, referral to a specialist is expected.

In 1999 the American Dental Association’s house of delegates voted to accept the application for specialty recognition from the AAOMR to create dentistry’s ninth specialty. Now clinicians have specialists in oral and maxillofacial radiology to whom they can refer difficult cases.

In essence, this signals a move to the medical model of radiographic imaging; that is, we are shifting the responsibility for the overall image findings to a qualified radiologist after more than 100 years of clinicians serving as their own radiology expert. Plain films and digital intraoral and panoramic images will still be used for some diagnostic procedures, but clinicians will probably need to enlist the services of an oral and maxillofacial radiologist to look at patient CBCT data for occult pathology in less familiar anatomical regions. It is both prudent and professional to do so. Table 1-1 shows the reportable findings in 381 CBCT cases in a 1-year period (March 2005 to March 2006).

Common CBCT concerns

How much data do you need?

This is a very difficult question to answer. Orthodontists or dentists who treat orthodontic problems in their patients require much more diagnostic information to assess a case and predict the outcome. Currently, orthodontic assessment usually involves intraoral images; panoramic, cephalometric, and sometimes hand-wrist radiographs; and plaster casts. Casts are mentioned because, in the future, clinicians will create 3D casts from the radiographic data in the cone beam scan. So the ability to acquire all the image data needed in one single imaging procedure offers orthodontists a very distinct advantage over current methods. Of course, the clinician does not always need all of those images on an 8-year-old patient at the initial record visit because it is unlikely that brackets will be placed on this patient until a few years later. Dentists should think about the information they need for each diagnostic task before they take or order a CBCT scan. This practice of applying selection criteria is only now becoming standard practice.⁴

How large an area do you wish to evaluate?

Some CBCT machines acquire larger data volumes than others. Data acquisitions range from volumes of 4 x 4 cm² to 22 x 22 cm². Figure 1-3 demonstrates the differences in size and region of the head corresponding to these volumes. Not all clinicians need to see the entire skull or would wish to be responsible for the occult pathology that might be encountered in the data volume (slice). Radiologists and others wishing to assess the patient’s data volume must scroll and be able to detect pathologic findings in as many as 512 slices (images) in three orthogonal planes (axial, sagittal, and coronal). Most clinicians are not comfortable with this task or do not have the time to look at such a large amount of information.

Fig 1-3 Comparison between the results from a small-volume machine versus those from a large-volume machine. (top) Axial slice of the middle of the condylar head. (bottom) Larger area at approximately the same level. Both volumes contain anatomical structures and cells, such as the middle ear, mastoid cells, airway, and vertebral bodies, all of which would require evaluation to determine whether pathology was present.

Do you simply need 2D grayscale information for your decision?

It may not be necessary to have 3D color information for decision making at all. The reconstruction of a panoramic image from a 250-MB data volume requires anywhere from 4 to 70 times the amount of x-rays needed for a traditional panoramic film or digital image. Therefore, a 2D digital panoramic radiograph from a full-featured panoramic machine can often suffice for the preliminary visualization of the patient’s dentition, bone, condyles, and related anatomy (Fig 1-4).

Fig 1-4 Digital panoramic radiograph of a developing mixed dentition. Except for the slightly ectopic resorption of the primary canine roots, the dentition is developing normally. This child would not need a cone beam scan to make this determination. The x-ray dose from the CBCT scan would not be justified when this panoramic image would suffice.

Does the diagnostic task really require CBCT?

The clinician must determine if CBCT is even necessary for a particular diagnostic task. Applications and clinical indications to help with this determination are discussed further in later chapters. Detection of caries does not require a cone beam scan. Periodontal bone loss can be evaluated by well-positioned bitewing and periapical radiographs. Some underestimation of the alveolar architecture may occur in plain film or digital intraoral radiography, but this task again does not require CBCT’s thin slice data to see bone problems. If a patient exhibits systemic disease or a set of risk factors that could accelerate the bone loss associated with periodontal disease, a cone beam scan may be indicated to detect the disease earlier or monitor the treatment success. However, noninvasive, diagnostic immunoassay tests performed on saliva could detect disease processes even earlier without exposing the patient to any x-rays. The clinician should carefully consider the precise indications for this imaging modality and fully expect the images produced to result in a positive finding that could affect a treatment outcome. Although x-ray doses are lower for any CBCT machine than traditional medical CT, not every patient will require a CBCT scan.⁴

Does every patient require this type of imaging?

The short answer is an emphatic no. Again, the clinician must consider the application and prescribe this imaging test only for those patients who would actually benefit from a precise measurement for an implant site or a better outcome prediction based on the data volume acquired. There are enough reasons to use CBCT.^5,6 Income generation is not one of them, nor is the production of “prettier images.”