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Image is Everything Eugene L. Antenucci, DDS, FAGD

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The introduction of radiography in dentistry by Dr. Edmond Kells in 1896 was a milestone in the evolution of the clinical scientific diagnosis of dental disease and pathology. Significant changes did not occur for nearly 100 years until Dr. Frances Mouyen utilized a CCD chip coupled with a scintillator and fiber-optic plate to create digital radiographic images for use in dentistry. This quantum leap from film-based to digitally rendered radiographic images paved the way for another – the introduction of practical, affordable and highly valuable three-dimensional radiographic imaging for everyday dental practice.

A good basic question to start with is "Why 3D?" Conventional two-dimensional periapical and panographic imaging in general dentistry forms the backbone of everyday clinical diagnosis and treatment planning – isn't this sufficient? The levels of acceptance and utilization of digitally created and rendered images is high, and dentists have successfully integrated digital imaging in dentistry. But 2D images have their limitations. A periapical, panographic or cephalometric image displays all of the information captured in its field of view, but all of the information is superimposed. From a single film it is impossible to determine where structures lie within that image – all are seen compressed within the same plane. Spatial relationships are unknown. In addition, image distortion is a major concern. In one study it was found that the degree of distortion existing between measurements and the periapical radiographs varied from eight to 24 percent, with an average distortion of 14 percent. The distortion from the panoramic radiographs varied from five to 39 percent, with an average distortion of 23.5 percent.¹

Three-dimensional imaging yields minimal distortion, with a 1:1 display of dental structures. Precision and accuracy is high. Dr. Godfrey Hounsfield of EMI Laboratories is credited with developing the technology in the 1970s. Known as "Computerized Axial Tomography" or CT Scans, it provided a high degree of precision in evaluating finite defined "slices" of areas studied. The equipment itself was large and generally affordable only by medical centers and hospitals. The cost was also much higher in terms of the radiation dose emitted per image. Today, CT imaging is being used extensively in medicine, however a recent study published in the "Archives of Internal Medicine" states CT scans have increased threefold since 1993 to approximately 70 million scans annually. The authors concluded "overall, we estimated that approximately 29,000… future cancers could be related to CT scans performed in the U.S. in 2007."²
During the same period of time, dentistry has witnessed the introduction and universal acceptance of implants, with sound protocols in place utilizing 3D imaging for implant diagnosis and treatment planning. A 2007 survey of general dentists reported that more than half of general dentists offer their patients dental implant surgery, and the large majority of general dentists restore dental implants. With so many general dentists both placing and restoring implants, the progression to affordable and practical in-house 3D radiology services becomes fully understandable, especially in light of the fact that the cone beam 3D technology available to dentists offers the added benefits of significantly lowering patient radiation doses, greatly increasing patient convenience, lowering patient cost, and giving complete control over implant diagnosis and treatment planning.

With implant dentistry serving as a catalyst, general dentists and specialists, began to purchase, incorporate and utilize 3D cone beam technology offered by an ever-increasing number of manufacturers. It quickly became apparent that the benefits extended far beyond implant dentistry, and actually encompassed virtually all phases of dentistry. Adding the third dimension entirely removes the limitations imposed by standard imaging, allowing for areas of interest and concern to be viewed accurately in their relative positions and without superimposition.

Two-dimensional digital radiographs are a compilation of data collected in the form of pixels, or picture elements. These are captured with CCD sensors, phosphor plate sensors or from scans of conventional film-based radiographs. Once in the computer and viewed on a monitor, a number of digital tools are used to evaluate the image diagnostically. Three-dimensional cone beam images are derived from voxels instead of pixels. Voxels are three-dimensional cubes of information. When many voxels are compiled into an image, digital tools allow viewing any portion of that image, from any axis. These images become virtual representations of the objects studied, and the diagnostic utility of these images is a quantum leap above its 2D counterparts (see image, top right).

As this digital periapical radiograph is enlarged, the individual pixels become evident. Pixels are "picture elements." They represent the smallest elements of a 2D image. Digital images such as radiographs and panoramic images are composed of megapixels.

Voxels are pixels with volume. While a pixel is a two-dimensional square, a voxel is a cube of information, which adds the third dimension to the acquired image. Voxels have X, Y and Z axes (width, height and depth). Each voxel represents the smallest component of the 3D image, with each being stacked, and each individually having the ability to be manipulated by software.

Cone beam images are acquired in the dental office in a manner very similar to taking a digital panographic image. Each cone beam manufacturer has proprietary equipment, with its own particular set of features. The main differences are found in the size of the equipment, the equipment's type of "detector" (flat panel or image intensifier), its ability to take both 2D and 3D images, or only 3D images, and the size of the volumes possible (either specific targeted areas or full view of the entire head).

Cone beam images allow for three distinct planes to be visualized, and software allows for any areas within those planes to be evaluated. In addition, virtual reality (VR) views depict the image's virtual reconstruction. Cone Beam Volumetric Tomography (CBVT) is ideal for dedicated imaging of the maxillofacial complex, using a pyramid-shaped beam to scan the entire region of interest in a single semicircle scan, as opposed to a medical CT that takes multiple axial slices in multiple full circle scans. During the scan, each image is generated using a short X-ray pulse instead of continuous radiation.

As general dentists incorporated cone beam imaging into their practices for implant treatment planning, they quickly found that 3D imaging was indispensible in a wide range of dental procedures. The utility in everyday dental practice is extensive, with applications in many areas of diagnosis and treatment planning, including endodontics, periodontics, orthodontics, implantology, dental and maxillofacial surgery and TMJ analysis. When fully integrated into practice, it becomes evident that there are many cases where the lack of the third dimension actually diminishes the level of care being rendered. In endodontics, fractured roots, periapical pathology and accessory canals can be visualized. In treatment planning for the extraction of third molars the proximity to the mandibular nerve becomes plainly evident. In the diagnosis of all types of pathology, visualizing the third dimension allows for a thorough understanding of the pathology's actual extent, position and relationship to adjacent anatomic structures. The third dimension is indispensible in understanding the cause of previously undiagnosed pain; in visualizing sinus pathology; in understanding the etiology of temporomandibular joint dysfunctions; in diagnosing the true extent of periodontal pathology and disease in localized areas. In orthodontics, the applications are extensive.

In implant treatment planning, the standard of care today for many practitioners is to recommend 3D imaging for implants for nearly every patient, leading to a strong argument that it becomes poor practice to plan implants without using 3D imaging.

The implication is not that 3D images are required for all patients, but rather that there are cases where two dimensions are simply insufficient, and the additional third dimension becomes the only means of providing an accurate diagnosis. The presence of this technology has forever altered dental diagnosis and treatment planning, and cone beam imaging has raised the bar and redefined the standard of care for many areas of dentistry. The following examples show the use of the wide range of applications of cone beam imaging in general practice.

In incorporating 3D technology, several important considerations need to be kept in mind:
  • Spatial requirements
  • Training
  • Computer hardware and software requirements
  • Budget considerations: cost and return on investment.
  • Office practice workflow protocols.
The ALARA Principle (As Low As Reasonably Achievable) needs to be followed in order to minimize radiation dosage through all reasonable methods. This starts with the device itself, and extends to a sound office protocol for use which keeps the following in mind:
  • Will simple 2D information suffice?
  • Is 3D information necessary for the diagnosis?
  • If 3D is necessary, what volume size will suffice?
  • How much data is needed?
  • Do you have the necessary training to read all information in the study?
Above all, patient wellbeing and safety must be kept in mind. While cone beam does emit much lower levels of radiation than a CT scan, it does yield higher doses of radiation than a digital full-mouth series or panographic image. Cone beam is not intended to replace 2D imaging, but to serve as an invaluable adjunct in achieving the highest possible level of care.












References
  1. Michael Sonick, DMD/James Abrahams, MD/Robert A. Faiella, DMD, MMSc , "A Comparison of the Accuracy of Periapical, Panoramic, and Computerized Tomographic Radiographs in Locating the Mandibular Canal" JOMI on CD-ROM (1997 ©Quintessence Pub. Co.), 1994 Vol. 9,
    No. 4 (455 - 460).
  2. Amy Berrington de González, DPhil; Mahadevappa Mahesh, MS, PhD; Kwang-Pyo Kim, PhD; Mythreyi Bhargavan, PhD; Rebecca Lewis, MPH; Fred Mettler, MD; Charles Land, PhD, Archives of Internal Medicine, "Projected Cancer Risks From Computed Tomographic Scans Performed in the United States in 2007", 2009;169(22):2071-2077.
Author’s Bio
Dr. Eugene L. Antenucci is a 1983 graduate of New York University College of Dentistry. Dr. Antenucci maintains a full-time private practice in Huntington, New York, where his state-of-the-art dental facility serves the patients of Huntington, and also is home to a continuing dental education training center for dentists as well as a commercial dental laboratory. Dr. Antenucci lectures internationally, conducting seminars in the clinical utilization of advanced technology in dentistry, as well as seminars in cosmetic dentistry, practice management, Cerec and laser training.
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